android快速遍历 android sdcard目录下所有文件名

public class AndroidSdCardActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        readFile();
    } 

    private void readFile() {
        File file = Environment.getExternalStorageDirectory();
        File[] files = file.listFiles();
        readFile(files);
    }
    
    private void readFile(final File[] files){
        if(files!=null && files.length>0){
            for(int i=0;i<files.length;i++){
                if(files[i].isDirectory()){
                    final int tag=i;
                    new Thread(new Runnable() {
                        @Override 
                        public void run() {
                            readFile(files[tag].listFiles());
                        }
                    }).start();
                     
                }else{
                    Log.d("name", files[i].getName());
                }
                if(i==files.length-1){
                    
                }
            }
        }
    }
}