File类中几个经常用到的方法

一、File类的一些常用方法：

 

1.createNewFile

 

public boolean createNewFile()

                      throws IOException

Atomically creates a new, empty file named by this abstract pathname if and only if a file with 

this name does not yet exist. The check for the existence of the file and the creation of the 

file if it does not exist are a single operation that is atomic with respect to all other 

filesystem activities that might affect the file.

Note: this method should not be used for file-locking, as the resulting protocol cannot be made 

to work reliably. The FileLock facility should be used instead.

 

Returns:

true if the named file does not exist and was successfully created; false if the named file 

 

already exists

Throws:

IOException - If an I/O error occurred

SecurityException - If a security manager exists and its SecurityManager.checkWrite

 

(java.lang.String) method denies write access to the file

Since:

1.2

 

 

2.delete

 

public boolean delete()

Deletes the file or directory denoted by this abstract pathname. If this pathname denotes a 

directory, then the directory must be empty in order to be deleted.

Returns:

true if and only if the file or directory is successfully deleted; false otherwise

 

 

 

3.renameTo

 

public boolean renameTo(File dest)

Renames the file denoted by this abstract pathname.

Many aspects of the behavior of this method are inherently platform-dependent: The rename 

operation might not be able to move a file from one filesystem to another, it might not be 

atomic, and it might not succeed if a file with the destination abstract pathname already 

exists. The return value should always be checked to make sure that the rename operation was 

successful.

 

Parameters:

dest - The new abstract pathname for the named file

Returns:

true if and only if the renaming succeeded; false otherwise

这个方法可以用来移动文件夹的同时，修改文件夹的名称（同样适用于文件）

 

 

 

 

 

二、几个容易混淆的方法

 

(1)getPath()与getAbsolutePath()的区别

public static void test1(){

        File file1 = new File(".\\test1.txt");

        File file2 = new File("D:\\workspace\\test\\test1.txt");

        System.out.println("-----默认相对路径：取得路径不同------");

        System.out.println(file1.getPath());

        System.out.println(file1.getAbsolutePath());

        System.out.println("-----默认绝对路径:取得路径相同------");

        System.out.println(file2.getPath());

        System.out.println(file2.getAbsolutePath());

 

}

 

得到的结果：

-----默认相对路径：取得路径不同------

.\test1.txt

D:\workspace\test\.\test1.txt

-----默认绝对路径:取得路径相同------

D:\workspace\test\test1.txt

D:\workspace\test\test1.txt

因为getPath()得到的是构造file的时候的路径。

getAbsolutePath()得到的是全路径

如果构造的时候就是全路径那直接返回全路径

如果构造的时候试相对路径，返回当前目录的路径+构造file时候的路径

 

(2).getAbsolutePath()和getCanonicalPath()的不同

public static void test2() throws Exception{

        File file = new File("..\\src\\test1.txt");

        System.out.println(file.getAbsolutePath());

        System.out.println(file.getCanonicalPath());

    }

得到的结果

D:\workspace\test\..\src\test1.txt

D:\workspace\src\test1.txt

可以看到CanonicalPath不但是全路径，而且把..或者.这样的符号解析出来。

 

(3).

public static void test3() throws Exception{

        File file = new File("D:\\Text.txt");

        System.out.println(file.getCanonicalPath());

    }

 

确定你的系统是Windows系统。

确定D盘下没有Text.txt这个文件，直接执行这段代码，得到的结果是:

D:\Text.txt

注意这里试大写的Text.txt

在D盘下建立一个文件，名叫text.txt，再次执行代码，得到结果

D:\text.txt

同样的代码得到不同的结果。

同时可以对比getAbsolutePath()看看，这个得到的结果是一样的。

 

原因：

window是大小写不敏感的，也就是说在windows上test.txt和Test.txt是一个文件，所以在windows上当文件不

 

存在时，得到的路径就是按照输入的路径。但当文件存在时，就会按照实际的情况来显示。这也就是建立文件

 

后和删除文件后会有不同的原因。文件夹和文件类似。