jerry的成長之路

例子

//假設我有一個檔案路徑是C:\\myDir\myFile.txt


File(String pathname)
//File myDir = new File("C:\\myDir")
//File myFile = new File("C:\\myDir\\myFile.txt")

File(File parent, String child)
//File myFile = new File("C:\\myDir","myFile.txt")

File(String parent, String child)
//File myDir = new File("C:\\myDir")
//File myFile = new File(myDir,"myFile.txt")

File(URI uri)

我在使用File建構元的時候

1. 並沒有實際在檔案系統中建立檔案
2. 沒有讀寫或修改檔案內容
3. 檔案可以已經存在獲釋後建立都沒有影響

File類別範例

package com.iii.jerry;

import java.io.File;

public class iotest {

	public static void main(String[] args) {
		File dir = new File("C:\\javawork2");//建立目錄物件
		String contents[]=dir.list();//取得目錄中的目錄與檔案陣列
		
		if(!dir.isDirectory()){//如果他"不"是目錄就回傳true，並說不是目錄，其餘false
			System.out.println("Not a directory");
		}else if (contents.length==0){//contents.length==0代表沒有任何檔案或是目錄，秀出為空
			System.out.println("目錄"+dir.getName()+"內無檔案");
		}else{
			for(int i = 0;i<contents.length; i++){//目錄和檔案名稱一個一個列出來
				System.out.println(contents[i]);
			}
		}
	}

}

路徑

The absolute path identifies the file uniquely on a file system. A canonical path is the simplest path that uniquely identifies the file on a file system.

We can use the getAbsolutePath() and getCanonicalPath() methods to get the absolute and canonical paths represented by a File object, respectively.

The code above generates the following result.

package com.iii.jerry;

import java.io.File;
import java.io.IOException;

public class path {
  public static void main(String[] args) {
    printFilePath("C:\\javawork2\\test.txt");
    printFilePath(".." + File.separator + "notes.txt");//File.separator會依照不同的os做改變window是"/"
  }

  public static void printFilePath(String pathname) {
    File f = new File(pathname);
    System.out.println("File  Name: " + f.getName());
    System.out.println("File  exists: " + f.exists());
    System.out.println("Absolute Path: " + f.getAbsolutePath());

    try {
      System.out.println("Canonical Path: " + f.getCanonicalPath());
    }

    catch (IOException e) {
      e.printStackTrace();
    }
  }
}

輸出結果:

File  Name: test.txt
File  exists: true
Absolute Path: C:\javawork2\test.txt
Canonical Path: C:\javawork2\test.txt
File  Name: notes.txt
File  exists: false
Absolute Path: D:\JDBC\workspace\Basic\..\notes.txt
Canonical Path: D:\JDBC\workspace\notes.txt

File separator

Different operating systems use a different character to separate two parts in a pathname.

For example, Windows uses a backslash (\) as a name separator in a pathname

The File class defines a constant named separator Char, which is the system-dependent name separator character.

We can use the File.separator Char constant to get the name separator as a character.

The File.separator constant gives we the name separator as a String.

Using the name separator in your program will make your Java code work on different platforms.