java foundation: 13, commonly used methods of the File class have? (With code examples)

What are the common methods File?

1, common construction method

(1) public File (String pathname ); // absolute path structure
(2) public File (String parent , String child); // relative path structure
(3) public File (File parent , String child); // if there is parent instance, first created. Then the relative path configuration.

public class demo02File {
	public static void main(String[] args) {
		String fatherPath = "D:/other";
		String name = "1.jpg";
		
		// 相对路径构造
		File src1 = new File(fatherPath, name);
		File src2 = new File(new File(fatherPath), "2.jpg");
		
		// 绝对路径构造
		File src3=new File("D:/other/3.jpg");
		
		//没有盘符：以user.dir构建
		File src4= new File("4.jpg");
		System.out.println(src4.getName());
		System.out.println(src4.getPath());
		System.out.println(src4.getAbsolutePath());
		
		//.表示当前路径
		File src5= new File(".");
		System.out.println(src5.getName());
		System.out.println(src5.getPath());
		System.out.println(src5.getAbsolutePath());
	}
}

The code run results:

4.jpg
4.jpg
D: \ mywork \ linlinjava \ javalearnig \ JavaStudy \ 4.jpg
.
.
D: \ mywork \ linlinjava \ javalearnig \ JavaStudy.

2, a method to obtain information

getPath (): get file path
getName (): get the last layer name, document name
getParent (): the path to get rid of the last layer, that parent directory file
getParentFile (): get the new parent file path

		String fatherPath = "D:/other";
		String name = "1.jpg";

		File src1 = new File(fatherPath, name);
		System.out.println("文件路径：" + src1.getPath());
		System.out.println("文件名：" + src1.getName());
		System.out.println("文件上层目录：" + src1.getParent());
		File file1 = src1.getParentFile();// 得到父类路径文件的新对象
		//String[] filesName = file1.list();// 返回路径下文件名的String数组
		//File[] files = file1.listFiles();//获取路径下文件组成的File数组

3, determination method

isDirectory () whether the folder
isFile () whether a file
exists () path exists
canWrite () is writable
canRead () is readable
length () file length? It can be used to determine whether a file, folder, length 0

		String fatherPath = "D:/other";
		String name = "1.jpg";
		File src1 = new File(fatherPath);
		File src2 = new File(fatherPath, name);
		System.out.println("是否存在？  "+src1.exists());
		System.out.println("是否是文件夹？  "+src1.isDirectory());
		System.out.println("是否是文件？  "+src2.isFile());
		System.out.println("文件是否可写？ " + src2.canWrite());
		System.out.println("文件是否可读？ " + src2.canRead());
		System.out.println("是否是绝对路径？ " + src1.isAbsolute());
		System.out.println("文件长度？  "+src1.length());// 文件的长度（字节数），文件夹长度为0，只有文件可以读取长度

4, create / delete files

createNewFile (); create a file
delete (); delete files
createTempFile (); create a temporary file
tempFile.deleteOnExit (); temporary files are automatically deleted after the program exits

	public static void test3() throws IOException, InterruptedException {
		String path = "D:/other/0.jpg";
		File f1 = new File(path);
		if (!f1.exists()) {
			boolean flag = f1.createNewFile();
			System.out.println(flag ? "创建成功" : "创建失败");
		} else {
			System.out.println("文件已存在！");
		}
		boolean flag = f1.delete();
		System.out.println(flag ? "删除成功" : "删除失败");
		//临时文件.
		File tempFile=File.createTempFile("tes", ".temp", new File("D:/other"));
		Thread.sleep(2000);
		tempFile.deleteOnExit();//程序退出后自动删除
		
	}

5, directory operation method

mkdir () Create a new folder, you can only create one
mkdirs () to create a new folder, you can multi-layer
list (): Returns the name of the array of the path to the file or folder
listFiles (): Returns the next file or the file path an array of File folder

/**
*代码功能：输出文件夹下的文件名称。
*输出文件夹下的文件路径。
*输出文件夹中的txt文件路径
**/
public class demo04File {

	public static void main(String[] args) {
		String path = "D:/other/test/mytest";
		File f1 = new File(path);
		f1.mkdir();// 创建目录，必须确保父目录存在，否则失败
		f1.mkdirs();// 创建目录，如果父目录不存在，一同创建
		if (f1.exists()) {
			System.out.println("=====子目录||子文件====");
			String[] names = f1.list();
			for (String temp : names) {
				System.out.println(temp);
			}
			
			System.out.println("=====子目录||子文件的file对象====");
			File[] files=f1.listFiles();
			for(File temp:files){
				System.out.println(temp.getAbsolutePath());
			}
			
			System.out.println("=====子目录||文件txt对象====");
			//命令设计模式
			File[] files1=f1.listFiles(new FilenameFilter() {
				/**
				 * dir代表f1
				 */
				@Override
				public boolean accept(File dir, String name) {
					return new File(dir,name).isFile()&& name.endsWith(".txt");
				}
			});
			for(File temp:files1){
				System.out.println(temp.getAbsolutePath());
			}
		}
	}
}

Code is run results:
=Sub-file subdirectory ||
1.docx
2.mpp
3.xlsx
4.txt
=file object subdirectory || sub-files
D:\other\test\mytest\1.docx
D:\other\test\mytest\2.mpp
D:\other\test\mytest\3.xlsx
D:\other\test\mytest\4.txt
=Txt file objects subdirectory ||
D:\other\test\mytest\4.txt