android 40 Io编程

package com.sxt.day06_06;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends Activity {
    EditText met;//文本框
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
        setListener();
    }
    private void setListener() {
        setSaveDataClickListener();
        setReadDataClickListener();
    }
    private void setReadDataClickListener() {
        findViewById(R.id.btnReadData).setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                FileInputStream in =null;
                try {
                    in= openFileInput("file.dat");
                    byte[] data=new byte[1024];
                    int len = in.read(data);//返回实际读取的字节数
                    String text=new String(data, 0, len, "utf-8");
                    Toast.makeText(MainActivity.this, text, 3000).show();
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }finally{
                    if(in!=null){
                        try {
                            in.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }
        });
    }
    private void setSaveDataClickListener() {
        findViewById(R.id.btnSaveData).setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                FileOutputStream out = null;
                try {
                    out=openFileOutput("file.dat", MODE_PRIVATE);
                    String text=met.getText().toString();
                    byte[] data=text.getBytes("utf-8");//FileOutputStream时data要转换为字节数组
                    out.write(data);
                    out.flush();
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                } catch (UnsupportedEncodingException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }finally{
                    if(out!=null){
                        try {
                            out.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }
        });
    }
    private void initView() {
        met=(EditText) findViewById(R.id.et);
    }
}

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <EditText 
        android:id="@+id/et"
           android:layout_width="match_parent"
           android:layout_height="wrap_content"
           android:text="哈罗，张飞！"/>
    <Button
        android:id="@+id/btnSaveData"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="保存数据" />

    <Button
        android:id="@+id/btnReadData"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="读取数据" />
    
</LinearLayout>