Bài 32: Tìm hiểu về lớp File trong Java

<br /><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><img alt="Untitled" class="bbCodeImage LbImage" src="http://android.vn/attachments/untitled-png.22672/" style="border: 0px; max-width: 100%;" /></div><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><br /></div><div align="left" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;">- Lớp File thường được dùng để lấy các thông tin về tập tin cũng như thư mục.</div><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">- Hình ảnh ở trên chắc chắn các bạn thấy rất quen thuộc, đó là quá trình 1 phần mềm duyệt thư mục và chờ người dùng tìm, chọn mở 1 file hoặc thư mục nào đó.</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">- Kiến thức ở mục này sẽ giúp các bạn hiểu bản chất các câu lệnh có thể làm được điều này, tuy nhiên nếu bạn chưa biết về lập trình giao diện trong Java thì chưa thể làm được, ở loạt bài viết về lập trình giao diện trong Java mình sẽ nhắc lại và cùng mọi người làm 1 chương trình</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">có thể duyệt được file, thư mục tương tự như hình ảnh trên!</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">**Chúng ta bắt đầu vào tìm hiểu về lớp File:</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif;"><span style="color: red;">1, Tạo đối tượng File từ đường dẫn tuyệt đối</span></span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">public File(String pathname)</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Ví dụ:</span><br /><div class="bbCodeBlock bbCodePHP" style="background-color: white; border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; border: 1px solid rgb(228, 228, 228); color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 1em 0px; padding: 0px; position: relative;"><div class="type" style="background-color: #009b00; background-image: url(http://android.vn/styles/soft_responsive_green/xenforo/gradients/category-23px-light.png); background-position: 50% 0%; background-repeat: repeat no-repeat; border-bottom-color: rgb(228, 228, 228); border-bottom-style: solid; border-bottom-width: 1px; border-top-left-radius: 4px; border-top-right-radius: 4px; color: white; font-size: 11px; margin: 0px; padding: 3px 8px;">PHP:</div><div class="code" style="border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; direction: ltr; font-family: Consolas, 'Courier New', Courier, monospace; font-size: 10pt; line-height: 1.24; margin: 0px; max-height: 500px; min-height: 30px; overflow: auto; padding: 10px; white-space: nowrap; word-wrap: normal;"><code style="font-style: inherit; font-weight: inherit; line-height: 13px; margin: 0px; padding: 0px;"><span style="color: black;"><span style="color: #0000bb;"></span><span style="color: #ff8000;">//Tạo trước thư mục "demo" trong ổ E, nếu không chương trình sẽ lỗi</span><span style="color: #0000bb;">File f </span><span style="color: #007700;">= new </span><span style="color: #0000bb;">File</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"E:\\demo\\androidvn.txt"</span><span style="color: #007700;">);</span><span style="color: #0000bb;">f</span><span style="color: #007700;">.</span><span style="color: #0000bb;">createNewFile</span><span style="color: #007700;">();</span></span></code></div></div><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif;"><span style="color: red;">2,</span></span><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;"> </span><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif;"><span style="color: red;">Tạo đối tượng File từ tên đường dẫn thu mục và tên tập tin trong thư mục đó</span></span><br /><div class="bbCodeBlock bbCodePHP" style="background-color: white; border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; border: 1px solid rgb(228, 228, 228); color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 1em 0px; padding: 0px; position: relative;"><div class="type" style="background-color: #009b00; background-image: url(http://android.vn/styles/soft_responsive_green/xenforo/gradients/category-23px-light.png); background-position: 50% 0%; background-repeat: repeat no-repeat; border-bottom-color: rgb(228, 228, 228); border-bottom-style: solid; border-bottom-width: 1px; border-top-left-radius: 4px; border-top-right-radius: 4px; color: white; font-size: 11px; margin: 0px; padding: 3px 8px;">PHP:</div><div class="code" style="border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; direction: ltr; font-family: Consolas, 'Courier New', Courier, monospace; font-size: 10pt; line-height: 1.24; margin: 0px; max-height: 500px; min-height: 30px; overflow: auto; padding: 10px; white-space: nowrap; word-wrap: normal;"><code style="font-style: inherit; font-weight: inherit; line-height: 13px; margin: 0px; padding: 0px;"><span style="color: black;"><span style="color: #0000bb;"></span><span style="color: #ff8000;">//Tạo trước thư mục "demo" trong ổ E, nếu không chương trình sẽ lỗi</span><span style="color: #0000bb;">File f </span><span style="color: #007700;">= new </span><span style="color: #0000bb;">File</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"E:\\demo"</span><span style="color: #007700;">,</span><span style="color: #dd0000;">"androidvn2.txt"</span><span style="color: #007700;">);</span><span style="color: #0000bb;">f</span><span style="color: #007700;">.</span><span style="color: #0000bb;">createNewFile</span><span style="color: #007700;">();</span></span></code></div></div><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif;"><span style="color: red;">3, Tạo đối tượng File từ một đối tượng File khác</span></span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">public File(File parent, String child)</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Ví dụ:</span><br /><div class="bbCodeBlock bbCodePHP" style="background-color: white; border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; border: 1px solid rgb(228, 228, 228); color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 1em 0px; padding: 0px; position: relative;"><div class="type" style="background-color: #009b00; background-image: url(http://android.vn/styles/soft_responsive_green/xenforo/gradients/category-23px-light.png); background-position: 50% 0%; background-repeat: repeat no-repeat; border-bottom-color: rgb(228, 228, 228); border-bottom-style: solid; border-bottom-width: 1px; border-top-left-radius: 4px; border-top-right-radius: 4px; color: white; font-size: 11px; margin: 0px; padding: 3px 8px;">PHP:</div><div class="code" style="border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; direction: ltr; font-family: Consolas, 'Courier New', Courier, monospace; font-size: 10pt; line-height: 1.24; margin: 0px; max-height: 500px; min-height: 30px; overflow: auto; padding: 10px; white-space: nowrap; word-wrap: normal;"><code style="font-style: inherit; font-weight: inherit; line-height: 13px; margin: 0px; padding: 0px;"><span style="color: black;"><span style="color: #0000bb;">File dir </span><span style="color: #007700;">= new </span><span style="color: #0000bb;">File </span><span style="color: #007700;">(</span><span style="color: #dd0000;">"E:\\demo"</span><span style="color: #007700;">);</span><span style="color: #0000bb;">File f </span><span style="color: #007700;">= new </span><span style="color: #0000bb;">File</span><span style="color: #007700;">(</span><span style="color: #0000bb;">dir</span><span style="color: #007700;">,</span><span style="color: #dd0000;">"androidvn3.txt"</span><span style="color: #007700;">);</span><span style="color: #0000bb;">f</span><span style="color: #007700;">.</span><span style="color: #0000bb;">createNewFile</span><span style="color: #007700;">();</span></span></code></div></div><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif;"><span style="color: red;">4, Tạo 1 thư mục với đường dẫn</span></span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Ví dụ:</span><br /><div class="bbCodeBlock bbCodePHP" style="background-color: white; border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; border: 1px solid rgb(228, 228, 228); color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 1em 0px; padding: 0px; position: relative;"><div class="type" style="background-color: #009b00; background-image: url(http://android.vn/styles/soft_responsive_green/xenforo/gradients/category-23px-light.png); background-position: 50% 0%; background-repeat: repeat no-repeat; border-bottom-color: rgb(228, 228, 228); border-bottom-style: solid; border-bottom-width: 1px; border-top-left-radius: 4px; border-top-right-radius: 4px; color: white; font-size: 11px; margin: 0px; padding: 3px 8px;">PHP:</div><div class="code" style="border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; direction: ltr; font-family: Consolas, 'Courier New', Courier, monospace; font-size: 10pt; line-height: 1.24; margin: 0px; max-height: 500px; min-height: 30px; overflow: auto; padding: 10px; white-space: nowrap; word-wrap: normal;"><code style="font-style: inherit; font-weight: inherit; line-height: 13px; margin: 0px; padding: 0px;"><span style="color: black;"><span style="color: #0000bb;">File f </span><span style="color: #007700;">= new </span><span style="color: #0000bb;">File</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"E:\\demo2"</span><span style="color: #007700;">);</span><span style="color: #0000bb;">f</span><span style="color: #007700;">.</span><span style="color: #0000bb;">mkdir</span><span style="color: #007700;">();</span></span></code></div></div><span style="background-color: white; color: red; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;"><span style="font-size: small;">5, Một số phương thức thường gặp của lớp File</span></span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><br /><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><img alt="Untit2" class="bbCodeImage LbImage" src="http://android.vn/attachments/untit2-png.22673/" style="border: 0px; max-width: 100%;" /></div><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif;"><span style="color: red;">6, Lấy danh sách tên các tập tin và thư mục con của đối tượng:</span></span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Ta sử dụng:</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><b style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">- public String[] list()</b><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">File đang xét và trả về trong một mảng.</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Ví dụ:</span><br /><div class="bbCodeBlock bbCodePHP" style="background-color: white; border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; border: 1px solid rgb(228, 228, 228); color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 1em 0px; padding: 0px; position: relative;"><div class="type" style="background-color: #009b00; background-image: url(http://android.vn/styles/soft_responsive_green/xenforo/gradients/category-23px-light.png); background-position: 50% 0%; background-repeat: repeat no-repeat; border-bottom-color: rgb(228, 228, 228); border-bottom-style: solid; border-bottom-width: 1px; border-top-left-radius: 4px; border-top-right-radius: 4px; color: white; font-size: 11px; margin: 0px; padding: 3px 8px;">PHP:</div><div class="code" style="border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; direction: ltr; font-family: Consolas, 'Courier New', Courier, monospace; font-size: 10pt; line-height: 1.24; margin: 0px; max-height: 500px; min-height: 30px; overflow: auto; padding: 10px; white-space: nowrap; word-wrap: normal;"><code style="font-style: inherit; font-weight: inherit; line-height: 13px; margin: 0px; padding: 0px;"><span style="color: black;"><span style="color: #0000bb;">package javaandroidvn</span><span style="color: #007700;">;<br /> </span><span style="color: #0000bb;">import java</span><span style="color: #007700;">.</span><span style="color: #0000bb;">io</span><span style="color: #007700;">.</span><span style="color: #0000bb;">File</span><span style="color: #007700;">;</span><span style="color: #0000bb;">import java</span><span style="color: #007700;">.</span><span style="color: #0000bb;">io</span><span style="color: #007700;">.</span><span style="color: #0000bb;">IOException</span><span style="color: #007700;">;<br /><br />public class </span><span style="color: #0000bb;">JavaAndroidVn </span><span style="color: #007700;">{<br /><br />    public static </span><span style="color: #0000bb;">void main</span><span style="color: #007700;">(</span><span style="color: #0000bb;">String</span><span style="color: #007700;">[] </span><span style="color: #0000bb;">args</span><span style="color: #007700;">) </span><span style="color: #0000bb;">throws IOException </span><span style="color: #007700;">{<br />        </span><span style="color: #ff8000;">//Tạo trước thư mục "demo" trong ổ E, tạo 1 vài file và thư mục trong đó<br />        </span><span style="color: #0000bb;">File dir </span><span style="color: #007700;">= new </span><span style="color: #0000bb;">File</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"E:\\demo"</span><span style="color: #007700;">);<br />        </span><span style="color: #0000bb;">File</span><span style="color: #007700;">[] </span><span style="color: #0000bb;">listFile </span><span style="color: #007700;">= </span><span style="color: #0000bb;">dir</span><span style="color: #007700;">.</span><span style="color: #0000bb;">listFiles</span><span style="color: #007700;">();<br /><br />        </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"Danh sách file trong thư mục E:\\demo là: "</span><span style="color: #007700;">);<br />        for (</span><span style="color: #0000bb;">int i </span><span style="color: #007700;">= </span><span style="color: #0000bb;">0</span><span style="color: #007700;">; </span><span style="color: #0000bb;">i </span><span style="color: #007700;">< </span><span style="color: #0000bb;">listFile</span><span style="color: #007700;">.</span><span style="color: #0000bb;">length</span><span style="color: #007700;">; </span><span style="color: #0000bb;">i</span><span style="color: #007700;">++) {<br />            if (</span><span style="color: #0000bb;">listFile</span><span style="color: #007700;">[</span><span style="color: #0000bb;">i</span><span style="color: #007700;">].</span><span style="color: #0000bb;">isFile</span><span style="color: #007700;">()) {<br />                </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #0000bb;">listFile</span><span style="color: #007700;">[</span><span style="color: #0000bb;">i</span><span style="color: #007700;">].</span><span style="color: #0000bb;">getName</span><span style="color: #007700;">());<br />            }<br />        }<br />        </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"Danh sách thưc mục trong thư mục E:\\demo là: "</span><span style="color: #007700;">);<br />        for (</span><span style="color: #0000bb;">int i </span><span style="color: #007700;">= </span><span style="color: #0000bb;">0</span><span style="color: #007700;">; </span><span style="color: #0000bb;">i </span><span style="color: #007700;">< </span><span style="color: #0000bb;">listFile</span><span style="color: #007700;">.</span><span style="color: #0000bb;">length</span><span style="color: #007700;">; </span><span style="color: #0000bb;">i</span><span style="color: #007700;">++) {<br />            if (</span><span style="color: #0000bb;">listFile</span><span style="color: #007700;">[</span><span style="color: #0000bb;">i</span><span style="color: #007700;">].</span><span style="color: #0000bb;">isDirectory</span><span style="color: #007700;">()) {<br />                </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #0000bb;">listFile</span><span style="color: #007700;">[</span><span style="color: #0000bb;">i</span><span style="color: #007700;">].</span><span style="color: #0000bb;">getName</span><span style="color: #007700;">());<br />            }<br />        }<br />    }<br />}</span></span></code></div></div><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><b>Tham khảo thêm 3 video của anh Việt bên blog StudyAndShare</b></div><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><br /></div><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><iframe allowfullscreen="" frameborder="0" height="300" src="http://www.youtube.com/embed/tyvp481FIxI?wmode=opaque" width="500"></iframe></div><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><br /></div><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><iframe allowfullscreen="" frameborder="0" height="300" src="http://www.youtube.com/embed/NHD5baBGR84?wmode=opaque" width="500"></iframe></div><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><br /></div><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><iframe allowfullscreen="" frameborder="0" height="300" src="http://www.youtube.com/embed/zk93GaheFg0?wmode=opaque" width="500"></iframe></div><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><br /></div><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><br /></div><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><img alt="[IMG]" class="bbCodeImage LbImage" src="http://android.vn/attachments/i-code-java-300x352-1705306-png.16732/" style="border: 0px; max-width: 100%;" /></div><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: medium;"><span style="color: red;">Bài tập về nhà:</span></span><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: medium;"><span style="color: red;"><b><img alt=":D" class="mceSmilieSprite mceSmilie8" src="http://android.vn/styles/default/xenforo/clear.png" style="background-image: url(http://android.vn/styles/default/xenforo/xenforo-smilies-sprite.png); background-position: -20px 0px; background-repeat: no-repeat no-repeat; border: 0px; height: 18px; margin: 0px 1px; vertical-align: text-bottom; width: 18px;" title="Big Grin :D" /></b></span></span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">(Lần này mình giao bài khó khó chút nhé)</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Tạo 1 chương trình gần giống cmd trong ms-dos chạy trên màn hình console, chức năng như sau:</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">- Bật chương trình lên mặc định vào ổ E (hoặc ổ nào tùy ý), hiện lên E:\\ (Tên đường đang hiện hành)</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">- Gõ "cd tenThuMuc" thì màn hình chuyển và hiện lên E:\\tenThuMuc trong đó tenThuMuc là tên thư mục tiếp tục muốn truy xuất.</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">- Gõ "makeFile tenFile" thì sẽ tạo file trong thư mục hiện hành, trong đó tenFile là tên file cần tạo.</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">- Từ vị trí con trỏ hiện hành, gõ "show" thì hiển thị ra toàn bộ cấu trúc cây thư mục trong thư mục đó.</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">....</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Trình bày khá dài dòng nhỉ, các bạn cứ cố gắng làm càng giống cmd trong ms-dos càng hay, bạn nào làm xong nhớ share mọi người cùng tham khảo nhé </span><img alt=":D" class="mceSmilieSprite mceSmilie8" src="http://android.vn/styles/default/xenforo/clear.png" style="background-color: white; background-image: url(http://android.vn/styles/default/xenforo/xenforo-smilies-sprite.png); background-position: -20px 0px; background-repeat: no-repeat no-repeat; border: 0px; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; height: 18px; line-height: 21px; margin: 0px 1px; vertical-align: text-bottom; width: 18px;" title="Big Grin :D" />

Bài 32: Tìm hiểu về lớp File trong Java

- Lớp File thường được dùng để lấy các thông tin về tập tin cũng như thư mục. - Hình ảnh ở trên chắc chắn các bạn thấy rất quen thuộc, đó là...

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Bài 31: Đọc/ghi file dùng luồng ký tự trong Java

<br /><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><img alt="144887966" class="bbCodeImage LbImage" src="http://android.vn/attachments/144887966-png.22669/" style="border: 0px; max-width: 100%;" /></div><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><br /></div><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">- Khi chúng ta thao tác với văn bản, có thể sử dụng luồng byte. Tuy nhiên thì sự lựa chọn tốt nhất không phải là nó mà là </span><a class="Tinhte_XenTag_TagLink" href="http://android.vn/tags/lu%E1%BB%93ng+k%C3%BD+t%E1%BB%B1/" style="background-color: white; border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; color: #009b00; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px -3px; padding: 0px 3px; text-decoration: none;">luồng ký tự</a><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">, việc sử dụng luồng ký tự có ưu điểm là thao tác trực tiếp trên các ký tự Unicode.</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">- Cụ thể ở bài này mình sẽ giới thiệu 2 lớp luồng thường dùng cho việc đọc , ghi dữ liệu file là FileReader và FileWriter</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: medium;"><span style="color: red;">1, Ghi dữ liệu xuống file văn bản!</span></span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><b style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Ví dụ:</b><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;"> Nhập danh sách tên của 1 lớp học và ghi chúng xuống file tên là "danhsach.txt". Việc đọc và ghi kết thúc khi người dùng nhập vào chuỗi "stop".</span><br /><div class="bbCodeBlock bbCodePHP" style="background-color: white; border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; border: 1px solid rgb(228, 228, 228); color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 1em 0px; padding: 0px; position: relative;"><div class="type" style="background-color: #009b00; background-image: url(http://android.vn/styles/soft_responsive_green/xenforo/gradients/category-23px-light.png); background-position: 50% 0%; background-repeat: repeat no-repeat; border-bottom-color: rgb(228, 228, 228); border-bottom-style: solid; border-bottom-width: 1px; border-top-left-radius: 4px; border-top-right-radius: 4px; color: white; font-size: 11px; margin: 0px; padding: 3px 8px;">PHP:</div><div class="code" style="border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; direction: ltr; font-family: Consolas, 'Courier New', Courier, monospace; font-size: 10pt; line-height: 1.24; margin: 0px; max-height: 500px; min-height: 30px; overflow: auto; padding: 10px; white-space: nowrap; word-wrap: normal;"><code style="font-style: inherit; font-weight: inherit; line-height: 13px; margin: 0px; padding: 0px;"><span style="color: black;"><span style="color: #0000bb;">package javaandroidvn</span><span style="color: #007700;">;<br /> </span><span style="color: #0000bb;">import java</span><span style="color: #007700;">.</span><span style="color: #0000bb;">io</span><span style="color: #007700;">.</span><span style="color: #0000bb;">BufferedReader</span><span style="color: #007700;">;</span><span style="color: #0000bb;">import java</span><span style="color: #007700;">.</span><span style="color: #0000bb;">io</span><span style="color: #007700;">.</span><span style="color: #0000bb;">FileWriter</span><span style="color: #007700;">;</span><span style="color: #0000bb;">import java</span><span style="color: #007700;">.</span><span style="color: #0000bb;">io</span><span style="color: #007700;">.</span><span style="color: #0000bb;">IOException</span><span style="color: #007700;">;</span><span style="color: #0000bb;">import java</span><span style="color: #007700;">.</span><span style="color: #0000bb;">io</span><span style="color: #007700;">.</span><span style="color: #0000bb;">InputStreamReader</span><span style="color: #007700;">;<br /><br />public class </span><span style="color: #0000bb;">JavaAndroidVn </span><span style="color: #007700;">{<br /><br />    public static </span><span style="color: #0000bb;">void main</span><span style="color: #007700;">(</span><span style="color: #0000bb;">String</span><span style="color: #007700;">[] </span><span style="color: #0000bb;">args</span><span style="color: #007700;">) </span><span style="color: #0000bb;">throws IOException </span><span style="color: #007700;">{<br />        </span><span style="color: #0000bb;">String str</span><span style="color: #007700;">;<br />        </span><span style="color: #0000bb;">FileWriter fw</span><span style="color: #007700;">;<br /><br />        </span><span style="color: #0000bb;">BufferedReader br </span><span style="color: #007700;">= new </span><span style="color: #0000bb;">BufferedReader</span><span style="color: #007700;">(<br />                new </span><span style="color: #0000bb;">InputStreamReader</span><span style="color: #007700;">(</span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">in</span><span style="color: #007700;">));<br /><br />        try {<br />            </span><span style="color: #0000bb;">fw </span><span style="color: #007700;">= new </span><span style="color: #0000bb;">FileWriter</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"E:\\danhsach.txt"</span><span style="color: #007700;">);<br />        } catch (</span><span style="color: #0000bb;">IOException exc</span><span style="color: #007700;">) {<br />            </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"Có lỗi xảy ra"</span><span style="color: #007700;">);<br />            return;<br />        }<br /><br />        </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"Nhập danh sách tên: ('stop' để kết thúc chương trình)"</span><span style="color: #007700;">);<br /><br />        do {<br />            </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.print(</span><span style="color: #dd0000;">": "</span><span style="color: #007700;">);<br />            </span><span style="color: #0000bb;">str </span><span style="color: #007700;">= </span><span style="color: #0000bb;">br</span><span style="color: #007700;">.</span><span style="color: #0000bb;">readLine</span><span style="color: #007700;">();<br />            if (</span><span style="color: #0000bb;">str</span><span style="color: #007700;">.</span><span style="color: #0000bb;">compareTo</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"stop"</span><span style="color: #007700;">) == </span><span style="color: #0000bb;">0</span><span style="color: #007700;">) {<br />                break;<br />            }<br />            </span><span style="color: #0000bb;">str </span><span style="color: #007700;">= </span><span style="color: #0000bb;">str </span><span style="color: #007700;">+ </span><span style="color: #dd0000;">"\n"</span><span style="color: #007700;">;  </span><span style="color: #ff8000;">//Dùng để xuống dòng khi nhập xong 1 chuỗi!<br />            </span><span style="color: #0000bb;">fw</span><span style="color: #007700;">.</span><span style="color: #0000bb;">write</span><span style="color: #007700;">(</span><span style="color: #0000bb;">str</span><span style="color: #007700;">);<br />        } while (</span><span style="color: #0000bb;">str</span><span style="color: #007700;">.</span><span style="color: #0000bb;">compareTo</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"stop"</span><span style="color: #007700;">) != </span><span style="color: #0000bb;">0</span><span style="color: #007700;">);<br /><br />        </span><span style="color: #0000bb;">fw</span><span style="color: #007700;">.</span><span style="color: #0000bb;">close</span><span style="color: #007700;">();<br />        </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"Bạn mở file ở đường dẫn E:\\danhsach.txt, dũ liệu đã được lưu!"</span><span style="color: #007700;">);<br /><br />    }<br />}</span></span></code></div></div><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: medium;"><span style="color: red;">2, Đọc dữ liệu từ File văn bản</span></span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><b style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Ví dụ:</b><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;"> Đọc và hiển thị nội dung của file "danhsach.txt" lên màn hình. Trong đó file là file văn bản, trong là danh sách tên ghi theo từng dòng! Chương trình sẽ đọc file văn bản từng dòng!</span><br /><div class="bbCodeBlock bbCodePHP" style="background-color: white; border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; border: 1px solid rgb(228, 228, 228); color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 1em 0px; padding: 0px; position: relative;"><div class="type" style="background-color: #009b00; background-image: url(http://android.vn/styles/soft_responsive_green/xenforo/gradients/category-23px-light.png); background-position: 50% 0%; background-repeat: repeat no-repeat; border-bottom-color: rgb(228, 228, 228); border-bottom-style: solid; border-bottom-width: 1px; border-top-left-radius: 4px; border-top-right-radius: 4px; color: white; font-size: 11px; margin: 0px; padding: 3px 8px;">PHP:</div><div class="code" style="border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; direction: ltr; font-family: Consolas, 'Courier New', Courier, monospace; font-size: 10pt; line-height: 1.24; margin: 0px; max-height: 500px; min-height: 30px; overflow: auto; padding: 10px; white-space: nowrap; word-wrap: normal;"><code style="font-style: inherit; font-weight: inherit; line-height: 13px; margin: 0px; padding: 0px;"><span style="color: black;"><span style="color: #0000bb;">package javaandroidvn</span><span style="color: #007700;">;<br /> </span><span style="color: #0000bb;">import java</span><span style="color: #007700;">.</span><span style="color: #0000bb;">io</span><span style="color: #007700;">.</span><span style="color: #0000bb;">BufferedReader</span><span style="color: #007700;">;</span><span style="color: #0000bb;">import java</span><span style="color: #007700;">.</span><span style="color: #0000bb;">io</span><span style="color: #007700;">.</span><span style="color: #0000bb;">FileReader</span><span style="color: #007700;">;</span><span style="color: #0000bb;">import java</span><span style="color: #007700;">.</span><span style="color: #0000bb;">io</span><span style="color: #007700;">.</span><span style="color: #0000bb;">IOException</span><span style="color: #007700;">;<br /><br />public class </span><span style="color: #0000bb;">JavaAndroidVn </span><span style="color: #007700;">{<br /><br />    public static </span><span style="color: #0000bb;">void main</span><span style="color: #007700;">(</span><span style="color: #0000bb;">String</span><span style="color: #007700;">[] </span><span style="color: #0000bb;">args</span><span style="color: #007700;">) </span><span style="color: #0000bb;">throws IOException </span><span style="color: #007700;">{<br />        try (</span><span style="color: #0000bb;">FileReader fr </span><span style="color: #007700;">= new </span><span style="color: #0000bb;">FileReader</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"E:\\danhsach.txt"</span><span style="color: #007700;">)) {<br />            </span><span style="color: #ff8000;">//Bạn có thể tạo dữ liệu văn bản dạng UTF-8 - Tiếng Việt<br />            </span><span style="color: #0000bb;">BufferedReader br </span><span style="color: #007700;">= new </span><span style="color: #0000bb;">BufferedReader</span><span style="color: #007700;">(</span><span style="color: #0000bb;">fr</span><span style="color: #007700;">);<br />            </span><span style="color: #0000bb;">String s</span><span style="color: #007700;">;<br />            </span><span style="color: #ff8000;">//Đọc từng dòng văn bản!<br />            </span><span style="color: #007700;">while ((</span><span style="color: #0000bb;">s </span><span style="color: #007700;">= </span><span style="color: #0000bb;">br</span><span style="color: #007700;">.</span><span style="color: #0000bb;">readLine</span><span style="color: #007700;">()) != </span><span style="color: #0000bb;">null</span><span style="color: #007700;">) {<br />                </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #0000bb;">s</span><span style="color: #007700;">);<br />            }<br />        }catch(</span><span style="color: #0000bb;">IOException e</span><span style="color: #007700;">){<br />            </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"Đã có lỗi xảy ra!"</span><span style="color: #007700;">);<br />        }<br /><br />    }<br />}</span></span></code></div></div><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><br /></div><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><br /></div><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><img alt="[IMG]" class="bbCodeImage LbImage" src="http://android.vn/attachments/i-code-java-300x352-1705306-png.16732/" style="border: 0px; max-width: 100%;" /></div><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: medium;"><span style="color: red;">Bài tập về nhà:</span></span><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: medium;"><span style="color: red;"><b><img alt=":D" class="mceSmilieSprite mceSmilie8" src="http://android.vn/styles/default/xenforo/clear.png" style="background-image: url(http://android.vn/styles/default/xenforo/xenforo-smilies-sprite.png); background-position: -20px 0px; background-repeat: no-repeat no-repeat; border: 0px; height: 18px; margin: 0px 1px; vertical-align: text-bottom; width: 18px;" title="Big Grin :D" /></b></span></span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Viết chương trình copy nội dung file "input.txt" sang file "output.txt" sử dụng cách đọc ghi văn bản!</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Bạn nào làm xong cố gắng bớt chút ít thời gian đăng lên cho các bạn khác cùng tham khảo nhé!</span>

Bài 31: Đọc/ghi file dùng luồng ký tự trong Java

- Khi chúng ta thao tác với văn bản, có thể sử dụng luồng byte. Tuy nhiên thì sự lựa chọn tốt nhất không phải là nó mà là  luồng ký tự , việ...

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Bài 30: Sử dụng luồng ký tự trong Java

<br /><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><img alt="download" class="bbCodeImage LbImage" src="http://android.vn/attachments/download-jpg.22637/" style="border: 0px; max-width: 100%;" /></div><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Ở những bài trước, mình đã giới thiệu với các bạn việc sử dụng luồng byte để nhập và xuất dữ liệu ký tự. Nhưng trong nhiều trường hợp luồng byte không phải là cách tốt nhất để quản lý nhập xuất dữ liệu ký tự. Trong lập trình Java có kiểu luồng ký tự phục vụ riêng cho việc nhập xuất dữ liệu trên luồng. Mức trên cùng là 2 lớp trừu tường </span><b style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Reader</b><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;"> và </span><b style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Writer</b><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">. Các lớp dẫn xuất từ </span><b style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Reader </b><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">và </span><b style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Writer</b><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;"> hỗ trợ thao tác trên các luồng ký tự Unicode.</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">- Những phương thức định nghĩa trong lớp trừu tượng</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><br /><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><img alt="Untitled" class="bbCodeImage LbImage" src="http://android.vn/attachments/untitled-png.22638/" style="border: 0px; max-width: 100%;" /></div><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Bài này sẽ là nhập xuất ký tự và chuỗi sử dụng luồng ký tự, bài sau mình sẽ giới thiệu cách đọc ghi file dùng luồng ký tự!</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: medium;"><span style="color: red;">1, Nhập Console dùng luồng ký tự:</span></span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">- Để đọc dữ liệu nhập từ Console thì lớp tốt nhất là lớp BufferdReader. Nhưng ở đây, chúng ta không có cách nào xây dựng 1 lớp </span><a class="Tinhte_XenTag_TagLink" href="http://android.vn/tags/bufferedreader/" style="background-color: white; border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; color: #009b00; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px -3px; padding: 0px 3px; text-decoration: none;">BufferedReader</a><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;"> trực tiếp từ System.in vì thế nên cần chuyển nó thành luồng ký tự bằng cách dùng InputStreamReader để chuyển byte thành ký tự!</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">- Để có được một đối tượng InputStreamReader gắn với System.in ta dùng constructor của InputStreamReader.</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><b style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">InputStreamReader(InputStream inputStream)</b><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">- Tiếp theo dùng đối tượng InputStreamReader đã tạo ra để tạo ra một BufferedReader dùng constructor BufferedReader.</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><b style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">BufferedReader(Reader inputReader)</b><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><b style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">**Ví dụ 1:</b><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;"> Tạo một đối tượng BufferedReader gắn với bàn phím:</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><b style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">BufferedReader br = new BufferedReader(new InputStreamReader(System.in));</b><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">- Sau khi thực hiện câu lệnh trên, br là một luồng ký tự gắn với Console thông qua System.in.</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Tiếp theo ta sẽ dùng BufferedReader để đọc từng ký tự từ Console. Việc đọc kết thúc khi gặp dấu chấm (dấu chấm để kết thúc chương trình).</span><br /><div class="bbCodeBlock bbCodePHP" style="background-color: white; border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; border: 1px solid rgb(228, 228, 228); color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 1em 0px; padding: 0px; position: relative;"><div class="type" style="background-color: #009b00; background-image: url(http://android.vn/styles/soft_responsive_green/xenforo/gradients/category-23px-light.png); background-position: 50% 0%; background-repeat: repeat no-repeat; border-bottom-color: rgb(228, 228, 228); border-bottom-style: solid; border-bottom-width: 1px; border-top-left-radius: 4px; border-top-right-radius: 4px; color: white; font-size: 11px; margin: 0px; padding: 3px 8px;">PHP:</div><div class="code" style="border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; direction: ltr; font-family: Consolas, 'Courier New', Courier, monospace; font-size: 10pt; line-height: 1.24; margin: 0px; max-height: 500px; min-height: 30px; overflow: auto; padding: 10px; white-space: nowrap; word-wrap: normal;"><code style="font-style: inherit; font-weight: inherit; line-height: 13px; margin: 0px; padding: 0px;"><span style="color: black;"><span style="color: #0000bb;">package javaandroidvn</span><span style="color: #007700;">;<br /> </span><span style="color: #0000bb;">import java</span><span style="color: #007700;">.</span><span style="color: #0000bb;">io</span><span style="color: #007700;">.</span><span style="color: #0000bb;">BufferedReader</span><span style="color: #007700;">;</span><span style="color: #0000bb;">import java</span><span style="color: #007700;">.</span><span style="color: #0000bb;">io</span><span style="color: #007700;">.</span><span style="color: #0000bb;">IOException</span><span style="color: #007700;">;</span><span style="color: #0000bb;">import java</span><span style="color: #007700;">.</span><span style="color: #0000bb;">io</span><span style="color: #007700;">.</span><span style="color: #0000bb;">InputStreamReader</span><span style="color: #007700;">;<br /><br />public class </span><span style="color: #0000bb;">JavaAndroidVn </span><span style="color: #007700;">{<br /><br />    public static </span><span style="color: #0000bb;">void main</span><span style="color: #007700;">(</span><span style="color: #0000bb;">String</span><span style="color: #007700;">[] </span><span style="color: #0000bb;">args</span><span style="color: #007700;">) </span><span style="color: #0000bb;">throws IOException </span><span style="color: #007700;">{<br />        </span><span style="color: #0000bb;">char c</span><span style="color: #007700;">;<br />        </span><span style="color: #0000bb;">BufferedReader br </span><span style="color: #007700;">= new </span><span style="color: #0000bb;">BufferedReader</span><span style="color: #007700;">(<br />                new </span><span style="color: #0000bb;">InputStreamReader</span><span style="color: #007700;">(</span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">in</span><span style="color: #007700;">));<br /><br />        </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"Nhập chuỗi ký tự, kết thúc bằng dấu chấm ."</span><span style="color: #007700;">);<br /><br />        do {<br />            </span><span style="color: #0000bb;">c </span><span style="color: #007700;">= (</span><span style="color: #0000bb;">char</span><span style="color: #007700;">) </span><span style="color: #0000bb;">br</span><span style="color: #007700;">.</span><span style="color: #0000bb;">read</span><span style="color: #007700;">();<br />            </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #0000bb;">c</span><span style="color: #007700;">);<br />        } while (</span><span style="color: #0000bb;">c </span><span style="color: #007700;">!= </span><span style="color: #dd0000;">'.'</span><span style="color: #007700;">);<br /><br />    }<br />}</span></span></code></div></div><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">**</span><b style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Ví dụ 2:</b><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;"> Dùng BufferedReader đọc chuỗi ký tự từ Console. In ký tự vừa nhập vào!</span><br /><div class="bbCodeBlock bbCodePHP" style="background-color: white; border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; border: 1px solid rgb(228, 228, 228); color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 1em 0px; padding: 0px; position: relative;"><div class="type" style="background-color: #009b00; background-image: url(http://android.vn/styles/soft_responsive_green/xenforo/gradients/category-23px-light.png); background-position: 50% 0%; background-repeat: repeat no-repeat; border-bottom-color: rgb(228, 228, 228); border-bottom-style: solid; border-bottom-width: 1px; border-top-left-radius: 4px; border-top-right-radius: 4px; color: white; font-size: 11px; margin: 0px; padding: 3px 8px;">PHP:</div><div class="code" style="border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; direction: ltr; font-family: Consolas, 'Courier New', Courier, monospace; font-size: 10pt; line-height: 1.24; margin: 0px; max-height: 500px; min-height: 30px; overflow: auto; padding: 10px; white-space: nowrap; word-wrap: normal;"><code style="font-style: inherit; font-weight: inherit; line-height: 13px; margin: 0px; padding: 0px;"><span style="color: black;"><span style="color: #0000bb;">package javaandroidvn</span><span style="color: #007700;">;<br /> </span><span style="color: #0000bb;">import java</span><span style="color: #007700;">.</span><span style="color: #0000bb;">io</span><span style="color: #007700;">.</span><span style="color: #0000bb;">BufferedReader</span><span style="color: #007700;">;</span><span style="color: #0000bb;">import java</span><span style="color: #007700;">.</span><span style="color: #0000bb;">io</span><span style="color: #007700;">.</span><span style="color: #0000bb;">IOException</span><span style="color: #007700;">;</span><span style="color: #0000bb;">import java</span><span style="color: #007700;">.</span><span style="color: #0000bb;">io</span><span style="color: #007700;">.</span><span style="color: #0000bb;">InputStreamReader</span><span style="color: #007700;">;<br /><br />public class </span><span style="color: #0000bb;">JavaAndroidVn </span><span style="color: #007700;">{<br /><br />    public static </span><span style="color: #0000bb;">void main</span><span style="color: #007700;">(</span><span style="color: #0000bb;">String</span><span style="color: #007700;">[] </span><span style="color: #0000bb;">args</span><span style="color: #007700;">) </span><span style="color: #0000bb;">throws IOException </span><span style="color: #007700;">{<br /><br />        </span><span style="color: #ff8000;">// Tạo đối tượng BufferedReader sử dụng System.in<br />        </span><span style="color: #0000bb;">BufferedReader br </span><span style="color: #007700;">= new </span><span style="color: #0000bb;">BufferedReader</span><span style="color: #007700;">(new </span><span style="color: #0000bb;">InputStreamReader</span><span style="color: #007700;">(</span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">in</span><span style="color: #007700;">));<br />        </span><span style="color: #0000bb;">String str</span><span style="color: #007700;">;<br />        </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.print(</span><span style="color: #dd0000;">"Nhập chuỗi: "</span><span style="color: #007700;">);<br />        </span><span style="color: #ff8000;">//Nhập chữ không dấu thôi nhé!<br />        </span><span style="color: #0000bb;">str </span><span style="color: #007700;">= </span><span style="color: #0000bb;">br</span><span style="color: #007700;">.</span><span style="color: #0000bb;">readLine</span><span style="color: #007700;">();<br />        </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"Chuỗi vừa nhập là: " </span><span style="color: #007700;">+ </span><span style="color: #0000bb;">str</span><span style="color: #007700;">);<br />    }<br />}</span></span></code></div></div><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: medium;"><span style="color: red;">2, Xuất dữ liệu ra Console dùng luồng ký tự</span></span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Tiếp tục sẽ là 1 cách khác để xuất dữ liệu ra Console. Ở đây mình nhắc tới lớp PrinWriter, nó là 1 trong các lớp luồng ký tự. Ta cần phải chỉ định System.out cho luồng xuất.</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><b style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">**Ví dụ 3:</b><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;"> Tạo đối tượng </span><a class="Tinhte_XenTag_TagLink" href="http://android.vn/tags/printwriter/" style="background-color: white; border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; color: #009b00; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px -3px; padding: 0px 3px; text-decoration: none;">PrintWriter</a><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;"> để xuất dữ liệu ra Console, dùng lệnh:</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">PrintWriter pw = new PrintWriter(System.out, true);</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Tiếp theo dùng PrintWriter để xuất dữ liệu ra Console</span><br /><div class="bbCodeBlock bbCodePHP" style="background-color: white; border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; border: 1px solid rgb(228, 228, 228); color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 1em 0px; padding: 0px; position: relative;"><div class="type" style="background-color: #009b00; background-image: url(http://android.vn/styles/soft_responsive_green/xenforo/gradients/category-23px-light.png); background-position: 50% 0%; background-repeat: repeat no-repeat; border-bottom-color: rgb(228, 228, 228); border-bottom-style: solid; border-bottom-width: 1px; border-top-left-radius: 4px; border-top-right-radius: 4px; color: white; font-size: 11px; margin: 0px; padding: 3px 8px;">PHP:</div><div class="code" style="border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; direction: ltr; font-family: Consolas, 'Courier New', Courier, monospace; font-size: 10pt; line-height: 1.24; margin: 0px; max-height: 500px; min-height: 30px; overflow: auto; padding: 10px; white-space: nowrap; word-wrap: normal;"><code style="font-style: inherit; font-weight: inherit; line-height: 13px; margin: 0px; padding: 0px;"><span style="color: black;"><span style="color: #0000bb;">package javaandroidvn</span><span style="color: #007700;">;<br /> </span><span style="color: #0000bb;">import java</span><span style="color: #007700;">.</span><span style="color: #0000bb;">io</span><span style="color: #007700;">.</span><span style="color: #0000bb;">IOException</span><span style="color: #007700;">;</span><span style="color: #0000bb;">import java</span><span style="color: #007700;">.</span><span style="color: #0000bb;">io</span><span style="color: #007700;">.</span><span style="color: #0000bb;">PrintWriter</span><span style="color: #007700;">;<br /><br />public class </span><span style="color: #0000bb;">JavaAndroidVn </span><span style="color: #007700;">{<br /><br />    public static </span><span style="color: #0000bb;">void main</span><span style="color: #007700;">(</span><span style="color: #0000bb;">String</span><span style="color: #007700;">[] </span><span style="color: #0000bb;">args</span><span style="color: #007700;">) </span><span style="color: #0000bb;">throws IOException </span><span style="color: #007700;">{<br />        </span><span style="color: #0000bb;">int i </span><span style="color: #007700;">= </span><span style="color: #0000bb;">2013</span><span style="color: #007700;">;<br />        </span><span style="color: #0000bb;">String str </span><span style="color: #007700;">= </span><span style="color: #dd0000;">"Android.Vn "</span><span style="color: #007700;">;<br />        </span><span style="color: #ff8000;">//Xuất dữ liệu sử dụng PrintWriter<br />        </span><span style="color: #0000bb;">PrintWriter pw </span><span style="color: #007700;">= new </span><span style="color: #0000bb;">PrintWriter</span><span style="color: #007700;">(</span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">, </span><span style="color: #0000bb;">true</span><span style="color: #007700;">);<br />        </span><span style="color: #0000bb;">pw</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"Using a PrintWriter."</span><span style="color: #007700;">);<br />        </span><span style="color: #0000bb;">pw</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #0000bb;">str</span><span style="color: #007700;">+</span><span style="color: #0000bb;">i</span><span style="color: #007700;">);<br /><br />    }<br />}</span></span></code></div></div><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><img alt="[IMG]" class="bbCodeImage LbImage" src="http://android.vn/attachments/i-code-java-300x352-1705306-png.16732/" style="border: 0px; max-width: 100%;" /></div><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: medium;"><span style="color: red;">Bài tập về nhà:</span></span><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: medium;"><span style="color: red;"><b><img alt=":D" class="mceSmilieSprite mceSmilie8" src="http://android.vn/styles/default/xenforo/clear.png" style="background-image: url(http://android.vn/styles/default/xenforo/xenforo-smilies-sprite.png); background-position: -20px 0px; background-repeat: no-repeat no-repeat; border: 0px; height: 18px; margin: 0px 1px; vertical-align: text-bottom; width: 18px;" title="Big Grin :D" /></b></span></span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Làm lại các ví dụ trên! Mọi thắc mắc các bạn có thể bình luận phía dưới, mọi người cùng nhau thảo luận!</span>

Bài 30: Sử dụng luồng ký tự trong Java

Ở những bài trước, mình đã giới thiệu với các bạn việc sử dụng luồng byte để nhập và xuất dữ liệu ký tự. Nhưng trong nhiều trường hợp luồng ...

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Bài 29: File truy cập ngẫu nhiên (Random Access Files) trong Java

<br /><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><img alt="RandomAccessFile-Hierarchy" class="bbCodeImage LbImage" src="http://android.vn/attachments/randomaccessfile-hierarchy-jpg.18384/" style="border: 0px; max-width: 100%;" /></div><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><br /></div><div align="left" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><span style="font-size: medium;"><span style="color: red;">1, <a class="Tinhte_XenTag_TagLink" href="http://android.vn/tags/random+access+files/" style="border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; color: #009b00; margin: 0px -3px; padding: 0px 3px; text-decoration: none;">Random Access Files</a>?</span></span></div><div align="left" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><br /></div><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">- Bên cạnh việc xử lý xuất nhập trên file theo kiểu tuần tự thông qua các luồng, java cũng hỗ trợ truy cập ngẫu nhiên nội dung của một file nào đó dùng RandomAccessFile.</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">- RandomAccessFile không dẫn xuất từ InputStream hay OutputStream mà nó hiện thực các interface DataInput, DataOutput (có định nghĩa các phương thức I/O cơ bản).</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">- RandomAccessFile hỗ trợ vấn đề định vị con trỏ file bên trong một file dùng phương thức seek(long newPos).</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: red; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;"><b>2, </b></span><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: medium;"><span style="color: red;">Ví dụ:</span></span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Bài này lý thuyết ngắn, nhưng ví dụ hơi dài, chủ yếu là đọc code để hiểu! </span><img alt=":D" class="mceSmilieSprite mceSmilie8" src="http://android.vn/styles/default/xenforo/clear.png" style="background-color: white; background-image: url(http://android.vn/styles/default/xenforo/xenforo-smilies-sprite.png); background-position: -20px 0px; background-repeat: no-repeat no-repeat; border: 0px; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; height: 18px; line-height: 21px; margin: 0px 1px; vertical-align: text-bottom; width: 18px;" title="Big Grin :D" /><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">Chương trình sau sẽ ghi 9 số kiểu double xuống file, rồi đọc lên theo thứ tự ngẫu nhiên. Các bạn xem code có chỗ nào không hiểu cứ bình luận phía dưới, mọi người cùng nhau giải quyết! ^^</span><br /><div class="bbCodeBlock bbCodePHP" style="background-color: white; border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; border: 1px solid rgb(228, 228, 228); color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 1em 0px; padding: 0px; position: relative;"><div class="type" style="background-color: #009b00; background-image: url(http://android.vn/styles/soft_responsive_green/xenforo/gradients/category-23px-light.png); background-position: 50% 0%; background-repeat: repeat no-repeat; border-bottom-color: rgb(228, 228, 228); border-bottom-style: solid; border-bottom-width: 1px; border-top-left-radius: 4px; border-top-right-radius: 4px; color: white; font-size: 11px; margin: 0px; padding: 3px 8px;">PHP:</div><div class="code" style="border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; border-top-left-radius: 5px; border-top-right-radius: 5px; direction: ltr; font-family: Consolas, 'Courier New', Courier, monospace; font-size: 10pt; line-height: 1.24; margin: 0px; max-height: 500px; min-height: 30px; overflow: auto; padding: 10px; white-space: nowrap; word-wrap: normal;"><code style="font-style: inherit; font-weight: inherit; line-height: 13px; margin: 0px; padding: 0px;"><span style="color: black;"><span style="color: #0000bb;">package javaandroidvn</span><span style="color: #007700;">;<br /> </span><span style="color: #0000bb;">import java</span><span style="color: #007700;">.</span><span style="color: #0000bb;">io</span><span style="color: #007700;">.*;<br /><br />class </span><span style="color: #0000bb;">JavaAndroidVn </span><span style="color: #007700;">{<br /><br />    public static </span><span style="color: #0000bb;">void main</span><span style="color: #007700;">(</span><span style="color: #0000bb;">String args</span><span style="color: #007700;">[]) </span><span style="color: #0000bb;">throws IOException </span><span style="color: #007700;">{<br />        </span><span style="color: #0000bb;">double data</span><span style="color: #007700;">[] = {</span><span style="color: #0000bb;">11.2</span><span style="color: #007700;">, </span><span style="color: #0000bb;">13.6</span><span style="color: #007700;">, </span><span style="color: #0000bb;">255.6</span><span style="color: #007700;">, </span><span style="color: #0000bb;">117.92</span><span style="color: #007700;">, </span><span style="color: #0000bb;">2007.96</span><span style="color: #007700;">, </span><span style="color: #0000bb;">8.9</span><span style="color: #007700;">, </span><span style="color: #0000bb;">9.9</span><span style="color: #007700;">, </span><span style="color: #0000bb;">10.0</span><span style="color: #007700;">, </span><span style="color: #0000bb;">100.6</span><span style="color: #007700;">};<br />        </span><span style="color: #0000bb;">double d</span><span style="color: #007700;">;<br />        </span><span style="color: #0000bb;">RandomAccessFile raf</span><span style="color: #007700;">;<br /><br />        try {<br />            </span><span style="color: #0000bb;">raf </span><span style="color: #007700;">= new </span><span style="color: #0000bb;">RandomAccessFile</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"E:\\random.dat"</span><span style="color: #007700;">, </span><span style="color: #dd0000;">"rw"</span><span style="color: #007700;">);<br />        } catch (</span><span style="color: #0000bb;">FileNotFoundException exc</span><span style="color: #007700;">) {<br />            </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"Cannot open file."</span><span style="color: #007700;">);<br />            return;<br />        }<br /><br />        </span><span style="color: #ff8000;">// Write values to the file.<br />        </span><span style="color: #007700;">for (</span><span style="color: #0000bb;">int i </span><span style="color: #007700;">= </span><span style="color: #0000bb;">0</span><span style="color: #007700;">; </span><span style="color: #0000bb;">i </span><span style="color: #007700;">< </span><span style="color: #0000bb;">data</span><span style="color: #007700;">.</span><span style="color: #0000bb;">length</span><span style="color: #007700;">; </span><span style="color: #0000bb;">i</span><span style="color: #007700;">++) {<br />            try {<br />                </span><span style="color: #0000bb;">raf</span><span style="color: #007700;">.</span><span style="color: #0000bb;">writeDouble</span><span style="color: #007700;">(</span><span style="color: #0000bb;">data</span><span style="color: #007700;">[</span><span style="color: #0000bb;">i</span><span style="color: #007700;">]);<br /><br />            } catch (</span><span style="color: #0000bb;">IOException exc</span><span style="color: #007700;">) {<br />                </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"Error writing to file."</span><span style="color: #007700;">);<br />                return;<br />            }<br />        }<br /><br />        try {</span><span style="color: #ff8000;">// Now, read back specific values<br />            </span><span style="color: #0000bb;">raf</span><span style="color: #007700;">.</span><span style="color: #0000bb;">seek</span><span style="color: #007700;">(</span><span style="color: #0000bb;">0 </span><span style="color: #007700;">* </span><span style="color: #0000bb;">8</span><span style="color: #007700;">); </span><span style="color: #ff8000;">// seek to first double<br />            </span><span style="color: #0000bb;">d </span><span style="color: #007700;">= </span><span style="color: #0000bb;">raf</span><span style="color: #007700;">.</span><span style="color: #0000bb;">readDouble</span><span style="color: #007700;">();<br />            </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"First value is " </span><span style="color: #007700;">+ </span><span style="color: #0000bb;">d</span><span style="color: #007700;">);<br />            </span><span style="color: #0000bb;">raf</span><span style="color: #007700;">.</span><span style="color: #0000bb;">seek</span><span style="color: #007700;">(</span><span style="color: #0000bb;">8 </span><span style="color: #007700;">* </span><span style="color: #0000bb;">1</span><span style="color: #007700;">); </span><span style="color: #ff8000;">// seek to second double<br />            </span><span style="color: #0000bb;">d </span><span style="color: #007700;">= </span><span style="color: #0000bb;">raf</span><span style="color: #007700;">.</span><span style="color: #0000bb;">readDouble</span><span style="color: #007700;">();<br />            </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"Second value is " </span><span style="color: #007700;">+ </span><span style="color: #0000bb;">d</span><span style="color: #007700;">);<br />            </span><span style="color: #0000bb;">raf</span><span style="color: #007700;">.</span><span style="color: #0000bb;">seek</span><span style="color: #007700;">(</span><span style="color: #0000bb;">8 </span><span style="color: #007700;">* </span><span style="color: #0000bb;">3</span><span style="color: #007700;">); </span><span style="color: #ff8000;">// seek to fourth double<br />            </span><span style="color: #0000bb;">d </span><span style="color: #007700;">= </span><span style="color: #0000bb;">raf</span><span style="color: #007700;">.</span><span style="color: #0000bb;">readDouble</span><span style="color: #007700;">();<br />            </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"Fourth value is " </span><span style="color: #007700;">+ </span><span style="color: #0000bb;">d</span><span style="color: #007700;">);<br />            </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">();<br /> </span><span style="color: #ff8000;">//Read All data  <br />            </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"Read all: "</span><span style="color: #007700;">);<br />            for (</span><span style="color: #0000bb;">int i </span><span style="color: #007700;">= </span><span style="color: #0000bb;">0</span><span style="color: #007700;">; </span><span style="color: #0000bb;">i </span><span style="color: #007700;">< </span><span style="color: #0000bb;">data</span><span style="color: #007700;">.</span><span style="color: #0000bb;">length</span><span style="color: #007700;">; </span><span style="color: #0000bb;">i</span><span style="color: #007700;">++) {<br />                </span><span style="color: #0000bb;">raf</span><span style="color: #007700;">.</span><span style="color: #0000bb;">seek</span><span style="color: #007700;">(</span><span style="color: #0000bb;">8 </span><span style="color: #007700;">* </span><span style="color: #0000bb;">i</span><span style="color: #007700;">); </span><span style="color: #ff8000;">// seek to ith double<br />                </span><span style="color: #0000bb;">d </span><span style="color: #007700;">= </span><span style="color: #0000bb;">raf</span><span style="color: #007700;">.</span><span style="color: #0000bb;">readDouble</span><span style="color: #007700;">();<br />                </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.print(</span><span style="color: #0000bb;">d </span><span style="color: #007700;">+ </span><span style="color: #dd0000;">" "</span><span style="color: #007700;">);<br />            }<br />            </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #dd0000;">""</span><span style="color: #007700;">);<br /> </span><span style="color: #ff8000;">// Now, read every other value.<br />            </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"Here is every other value: "</span><span style="color: #007700;">);<br />            for (</span><span style="color: #0000bb;">int i </span><span style="color: #007700;">= </span><span style="color: #0000bb;">0</span><span style="color: #007700;">; </span><span style="color: #0000bb;">i </span><span style="color: #007700;">< </span><span style="color: #0000bb;">data</span><span style="color: #007700;">.</span><span style="color: #0000bb;">length</span><span style="color: #007700;">; </span><span style="color: #0000bb;">i </span><span style="color: #007700;">+= </span><span style="color: #0000bb;">2</span><span style="color: #007700;">) {<br />                </span><span style="color: #0000bb;">raf</span><span style="color: #007700;">.</span><span style="color: #0000bb;">seek</span><span style="color: #007700;">(</span><span style="color: #0000bb;">8 </span><span style="color: #007700;">* </span><span style="color: #0000bb;">i</span><span style="color: #007700;">); </span><span style="color: #ff8000;">// seek to ith double<br />                </span><span style="color: #0000bb;">d </span><span style="color: #007700;">= </span><span style="color: #0000bb;">raf</span><span style="color: #007700;">.</span><span style="color: #0000bb;">readDouble</span><span style="color: #007700;">();<br />                </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.print(</span><span style="color: #0000bb;">d </span><span style="color: #007700;">+ </span><span style="color: #dd0000;">" "</span><span style="color: #007700;">);<br />            }<br /><br /><br />            </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"\n"</span><span style="color: #007700;">);<br />        } catch (</span><span style="color: #0000bb;">IOException exc</span><span style="color: #007700;">) {<br />            </span><span style="color: #0000bb;">System</span><span style="color: #007700;">.</span><span style="color: #0000bb;">out</span><span style="color: #007700;">.</span><span style="color: #0000bb;">println</span><span style="color: #007700;">(</span><span style="color: #dd0000;">"Error seeking or reading."</span><span style="color: #007700;">);<br />        }<br /><br />        </span><span style="color: #0000bb;">raf</span><span style="color: #007700;">.</span><span style="color: #0000bb;">close</span><span style="color: #007700;">();<br />    }<br />}</span></span></code></div></div><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><div align="center" style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px; margin: 0px; padding: 0px;"><img alt="[IMG]" class="bbCodeImage LbImage" src="http://android.vn/attachments/i-code-java-300x352-1705306-png.16732/" style="border: 0px; max-width: 100%;" /></div><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: medium;"><span style="color: red;">Bài tập về nhà:</span></span><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: medium;"><span style="color: red;"><b><img alt=":D" class="mceSmilieSprite mceSmilie8" src="http://android.vn/styles/default/xenforo/clear.png" style="background-image: url(http://android.vn/styles/default/xenforo/xenforo-smilies-sprite.png); background-position: -20px 0px; background-repeat: no-repeat no-repeat; border: 0px; height: 18px; margin: 0px 1px; vertical-align: text-bottom; width: 18px;" title="Big Grin :D" /></b></span></span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">- Tạo chương trình khi chạy lên nếu như không tồn tại file thì tạo file mới như sau:</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">- Tạo 1 mảng , các phần tử là các số thực. Các số được ghi vào file theo kiểu ghi ngẫu nhiên.</span><br style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;" /><span style="background-color: white; color: #141414; font-family: Roboto, arial, sans-serif; font-size: 15px; line-height: 21px;">- Nếu file đã tồn tại, hoặc là ở những lần chạy sau, sau khi đã khởi tạo giá trị, chương trình bỏ qua bước khởi tạo và dựa vào file in ra những số có chỉ số lẻ trong mảng đã nhập trên bằng cách lấy trực tiếp chỉ số khi đọc file theo cách đọc ngẫu nhiên! (Không dùng cách nạp lại cả file vào mảng)</span>

Bài 29: File truy cập ngẫu nhiên (Random Access Files) trong Java

1,  Random Access Files ? - Bên cạnh việc xử lý xuất nhập trên file theo kiểu tuần tự thông qua các luồng, java cũng hỗ trợ truy cập ngẫu nh...

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