Files文件存储和读取

package com.hanqi.testapp111;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.PrintStream;

public class FilesActivity extends AppCompatActivity {
    EditText et_1;
    TextView tv_1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_files);
        et_1=(EditText)findViewById(R.id.et_1);
        tv_1=(TextView)findViewById(R.id.tv_1);
    }
    public void bt2_OnClick(View v)
    {try
    {
        File file=getFilesDir();
        String path=file.getAbsolutePath();
        FileOutputStream fos =openFileOutput("test.txt", MODE_APPEND);
        PrintStream ps =new PrintStream(fos);
        String str=et_1.getText().toString();
        ps.print(str);
        ps.close();
        fos.close();
        Toast.makeText(FilesActivity.this, "保存成功", Toast.LENGTH_SHORT).show();
    }catch (Exception e)
    {
        Toast.makeText(FilesActivity.this, "保存失败", Toast.LENGTH_SHORT).show();
    }

    }
    public void bt3_OnClick(View v)
    {
        try
        {
            FileInputStream fis =openFileInput("test.txt");
            byte[] b=new byte[1024];
            String str1="";
            int i=0;
            while ((i=fis.read(b))>0)
            {
                String str=new String(b,0,i);
                str1+=str;
            }
            fis.close();
            tv_1.setText(str1);
        }catch (Exception e)
        {

        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.hanqi.testapp111.FilesActivity"
    android:orientation="vertical">
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        android:id="@+id/tv_1"/>
    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="输入..."
        android:id="@+id/et_1"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="写内部文件"
        android:onClick="bt2_OnClick"
        />
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="读内部文件"
        android:onClick="bt3_OnClick"
        />

</LinearLayout>