MainActivity.java

import java.io.File;
import java.io.IOException;

import android.os.Bundle;
import android.app.Activity;
import android.util.Log;
import android.view.Menu;
import android.widget.Toast;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
//      File file = new File("/mnt/sdcard/test");
//      if (!file.exists()) {
//          try {
//              file.createNewFile();
//          } catch (IOException e) {
//              // TODO Auto-generated catch block
//              e.printStackTrace();
//          }
//      }else {
//          Toast.makeText(MainActivity.this, "文件已經(jīng)存在", 1000);
//      }
//      file.delete();
        
//          File file = this.getFilesDir();//這個(gè)目錄是當(dāng)前應(yīng)用程序默認(rèn)的數(shù)據(jù)存儲(chǔ)目錄
//          Log.i("info", file.toString());
//      File file = this.getCacheDir();//這個(gè)目錄是當(dāng)前應(yīng)用程序默認(rèn)的緩存文件的存放位置
//      //把一些不是非常重要的文件在此處創(chuàng)建 使用
//      //如果手機(jī)的內(nèi)存不足的時(shí)候 系統(tǒng)會(huì)自動(dòng)去刪除APP的cache目錄的數(shù)據(jù)
//      Log.i("info", file.toString());
//      /data/data/<包名>/app_imooc
//      File file = this.getDir("imooc", MODE_PRIVATE);
//      Log.i("info", file.toString());
//      this.getExternalFilesDir(type);
        //可以得到外部的存儲(chǔ)位置 該位置的數(shù)據(jù)跟內(nèi)置的使用是一樣的
        //如果APP卸載了 這里面的數(shù)據(jù)也會(huì)自動(dòng)清除掉
        File file = this.getExternalCacheDir();
        Log.i("info", file.toString());
    //如果說開發(fā)者不遵守這樣的規(guī)則 不把數(shù)據(jù)放入 data/data/<包名>
//          /mnt/sdcard/Android/data/<包名>
//      卸載之后數(shù)據(jù)將不會(huì)自動(dòng)清除掉 將會(huì)造成所謂的數(shù)據(jù)垃圾
    }

    

}

MainActivity.java

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

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends Activity {
    EditText edt;
    Button but;
    TextView contentvalue;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        edt = (EditText) findViewById(R.id.editText1);
        but = (Button) findViewById(R.id.write);
        contentvalue = (TextView) findViewById(R.id.contentvalue);
        but.setOnClickListener(new OnClickListener() {
            
            @Override
            public void onClick(View v) {
                WriteFiles(edt.getText().toString());
                contentvalue.setText(readFiles());
                
            }
        });
    }
    //保存文件內(nèi)容
    public void WriteFiles(String content){
         try {
            FileOutputStream fos = openFileOutput("a.txt", MODE_WORLD_READABLE+MODE_WORLD_WRITEABLE);
             fos.write(content.getBytes());
             fos.close();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
         
    }
    //讀取文件內(nèi)容
    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) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
        return content;
    }
}

main_activity.xml

<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=".MainActivity" >

    <EditText
        android:id="@+id/editText1"
        android:layout_width="wrap_content"
        android:layout_height="200dp"
        android:layout_alignParentLeft="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:ems="10" >

        <requestFocus />
    </EditText>

    <Button
        android:id="@+id/write"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:text="寫入并讀取出來" />

    <TextView
        android:id="@+id/contentvalue"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/editText1"
        android:layout_below="@+id/write"
        android:text="TextView" />

</RelativeLayout>

演示效果：

file.gif