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>