File类完全解析

• A:File类的概述
  • File更应该叫做一个路径
    • 文件路径或者文件夹路径
    • 路径分为绝对路径和相对路径
    • 绝对路径是一个固定的路径,从盘符开始
    • 相对路径相对于某个位置,在eclipse下是指当前项目下,在dos下
  • 查看API指的是当前路径
  • 文件和目录路径名的抽象表示形式
• B:构造方法
  • File(String pathname)：根据一个路径得到File对象
  • File(String parent, String child):根据一个目录和一个子文件/目录得到File对象
  • File(File parent, String child):根据一个父File对象和一个子文件/目录得到File对象

  if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
            logE("未挂载");
            String path = Environment.getExternalStorageDirectory().getPath()+"/DCIM/Camera";
            File file1 = new File(path);
            logE(file1.exists()+"");
            logE(file1.getAbsolutePath()+"");
            logE(file1.isFile()+"");
            logE(file1.isDirectory()+"");

            logE("----------------------------------------");
            path+="/20180823_123209.jpg";
            File file2 = new File(path);
            logE(file2.exists()+"");
            logE(file2.getAbsolutePath()+"");
            logE(file2.isFile()+"");
            logE(file2.isDirectory()+"");

            File file3 = new File(Environment.getExternalStorageDirectory(),"/DCIM/Camera/20180823_123209.jpg");
            logE(file3.exists()+"");
            logE(file3.getAbsolutePath()+"");
            logE(file3.isFile()+"");
            logE(file3.isDirectory()+"");
        }else {
            logE("挂载");
        }

08-23 12:48:49.441 23362-23362/com.chinamall21.mobile.javastudy E/study:: 未挂载
08-23 12:48:49.441 23362-23362/com.chinamall21.mobile.javastudy E/study:: true
08-23 12:48:49.441 23362-23362/com.chinamall21.mobile.javastudy E/study:: /storage/sdcard0/DCIM/Camera
08-23 12:48:49.441 23362-23362/com.chinamall21.mobile.javastudy E/study:: false
08-23 12:48:49.441 23362-23362/com.chinamall21.mobile.javastudy E/study:: true
08-23 12:48:49.441 23362-23362/com.chinamall21.mobile.javastudy E/study:: ----------------------------------------
08-23 12:48:49.446 23362-23362/com.chinamall21.mobile.javastudy E/study:: true
08-23 12:48:49.446 23362-23362/com.chinamall21.mobile.javastudy E/study:: /storage/sdcard0/DCIM/Camera/20180823_123209.jpg
08-23 12:48:49.446 23362-23362/com.chinamall21.mobile.javastudy E/study:: true
08-23 12:48:49.446 23362-23362/com.chinamall21.mobile.javastudy E/study:: false
08-23 12:48:49.446 23362-23362/com.chinamall21.mobile.javastudy E/study:: true
08-23 12:48:49.446 23362-23362/com.chinamall21.mobile.javastudy E/study:: /storage/sdcard0/DCIM/Camera/20180823_123209.jpg
08-23 12:48:49.446 23362-23362/com.chinamall21.mobile.javastudy E/study:: true
08-23 12:48:49.446 23362-23362/com.chinamall21.mobile.javastudy E/study:: false

• A:创建功能
  • public boolean createNewFile():创建文件 如果存在这样的文件，就不创建了
  • public boolean mkdir():创建文件夹 如果存在这样的文件夹，就不创建了
  • public boolean mkdirs():创建文件夹,如果父文件夹不存在，会帮你创建出来
    建立的是一个文件:

     File file = new File(Environment.getExternalStorageDirectory(),"test.txt");
        logE(file.exists()+"");
        try {
            logE(file.createNewFile());
            logE(file.exists());
        } catch (IOException e) {
            logE("catch");
            e.printStackTrace();
        }

建立的是一个文件夹:

 File file = new File(Environment.getExternalStorageDirectory(),"aaa");
 file.mkdir();

建立的是多级文件夹

 File file = new File(Environment.getExternalStorageDirectory(),"aaa/ddd");
 file.mkdirs();