通过在Android中指定文件夹路径，如何移动到外部SD卡中的文件夹

Button buttonFom = (Button) findViewById(R.id.fom);
    buttonFom.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {

            getDir(\"/mnt/sdcard/external_sd/DOC1/HW 850Xp/\");
        }
    });


private void getDir(String dirPath) {
    myPath.setText(\"Location: \" + dirPath);

    item = new ArrayList<String>();
    path = new ArrayList<String>();

    File f = new File(dirPath);
    File[] files = f.listFiles();

    if (!dirPath.equals(root)) {

        item.add(root);
        path.add(root);

        item.add(\"../\");
        path.add(f.getParent());

    }

    for (int i = 0; i < files.length; i++) {
        File file = files[i];
        path.add(file.getPath());
        if (file.isDirectory())
            item.add(file.getName() + \"/\");
        else
            item.add(file.getName());
    }

    ArrayAdapter<String> fileList = new ArrayAdapter<String>(this,
            R.layout.row, item);
    setListAdapter(fileList);
}