package com.example.file;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.util.Log;import android.view.View;import android.widget.Button;import android.widget.EditText;import android.widget.TextView;import android.widget.Toast;import java.io.ByteArrayOutputStream;import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;public class MainActivity extends AppCompatActivity {  EditText edt;  Button btn;  TextView tv;  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    edt = (EditText) findViewById(R.id.editText);    btn = (Button) findViewById(R.id.button);    tv = (TextView) findViewById(R.id.textView);    btn.setOnClickListener(new View.OnClickListener() {      @Override      public void onClick(View view) {        WriteFiles(edt.getText().toString());        tv.setText(readFiles());      }    });  }  //保存文件內容  public void WriteFiles(String content){    try {      FileOutputStream fos = openFileOutput("a.txt",MODE_PRIVATE);      fos.write(content.getBytes());      fos.close();    } catch (FileNotFoundException e) {      e.printStackTrace();    } catch (IOException e) {      e.printStackTrace();    }  }  //讀取文件  public String readFiles(){    String content = null;    try {      FileInputStream fis = openFileInput("a.txt");      ByteArrayOutputStream baos = new ByteArrayOutputStream();      byte[]buffer = new byte[1024];      int len = 0;      while ((len = fis.read(buffer))!=-1)      {        baos.write(buffer,0,len);      }      content = baos.toString();      fis.close();;      baos.close();    } catch (FileNotFoundException e) {      e.printStackTrace();    } catch (IOException e) {      e.printStackTrace();    }    return content;  }}

<?xml version="1.0" encoding="utf-8"?><RelativeLayout 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.example.file.MainActivity">  <EditText    android:layout_width="wrap_content"    android:layout_height="200dp"    android:id="@+id/editText"    android:layout_alignParentTop="true"    android:layout_alignParentLeft="true"    android:layout_alignParentStart="true"    android:layout_alignParentRight="true"    android:layout_alignParentEnd="true" />  <Button    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:text="New Button"    android:id="@+id/button"    android:layout_below="@+id/editText"    android:layout_centerHorizontal="true"    android:layout_marginTop="90dp" />  <TextView    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:text="New Text"    android:id="@+id/textView"    android:layout_below="@+id/button"    android:layout_alignParentRight="true"    android:layout_alignParentEnd="true"    android:layout_alignParentBottom="true"    android:layout_alignParentLeft="true"    android:layout_alignParentStart="true" /></RelativeLayout>