效果图：

.java文件有MainActivity.java、FileService.java、FileServiceTest.java， .xml文件有activity_main.xml。

本次注重AndroidTestCase类的使用，在开发中非常实用。用于测试某一功能。

使用AndroidTestCase类，有如下的要求：

1.在AndroidManifest.xml文件中，<manifest></manifest>中添加如下：

    <instrumentation
        android:name="android.test.InstrumentationTestRunner"
        android:targetPackage="com.example.l3_files" >
    </instrumentation>

 <uses-library android:name="android.test.runner" />

MainAcitity.java

package com.example.l3_files;

import android.os.Bundle;
import android.app.Activity;
import android.app.Notification;
import android.app.NotificationManager;
import android.app.PendingIntent;
import java.io.IOException;
import com.example.l3_files.model.FileService;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends Activity {

	private FileService fileService;
	private Button saveButton;
	NotificationManager notificationManager;
	Notification notification;
	PendingIntent pendingIntent;

	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		fileService = new FileService(this);

		saveButton = (Button) this.findViewById(R.id.save);

		notificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);

		pendingIntent = PendingIntent
				.getActivity(MainActivity.this, 0, null, 0);

		notification = new Notification();

		saveButton.setOnClickListener(new View.OnClickListener() {

			@Override
			public void onClick(View v) {
				EditText fileNameText = (EditText) findViewById(R.id.filename);
				EditText fileContentText = (EditText) findViewById(R.id.filecontent);

				String fileName = fileNameText.getText().toString();
				String fileContent = fileContentText.getText().toString();

				try {
					fileService.save(fileName, fileContent);
					Toast.makeText(MainActivity.this, R.string.success,
							Toast.LENGTH_LONG).show();
				} catch (IOException e) {
					e.printStackTrace();
					Toast.makeText(MainActivity.this, R.string.failure,
							Toast.LENGTH_LONG).show();
				}

				notification.icon = R.drawable.ic_launcher;
				notification.tickerText = "文件保存成功";
				notification.setLatestEventInfo(MainActivity.this, fileName,
						fileContent, pendingIntent);
				notificationManager.notify(0, notification);
			}

		});
	}

}

package com.example.l3_files.model;

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

import android.content.Context;

public class FileService {

	private Context context;

	public FileService(Context context) {
		super();
		this.context = context;
	}
	/**
	 * 保存文件
	 * @param filename 文件名称
	 * @param filecontent 文件内容
	 * @throws IOException
	 */
	public void save(String filename,String filecontent) throws IOException{
		//第1个参数是文件的名称，第2个参数是操作模式
		FileOutputStream fos=context.openFileOutput(filename, Context.MODE_WORLD_WRITEABLE+Context.MODE_WORLD_READABLE);
		fos.write(filecontent.getBytes());
		fos.close();
	}
	
	public String readFile(String filename) throws IOException{
		FileInputStream fis=context.openFileInput(filename);
		int len=0;
		byte[] buffer=new byte[1024];
		ByteArrayOutputStream baos=new ByteArrayOutputStream();//往内存中输出数据的
		while((len=fis.read(buffer))!=-1)//如果数据量很大，第2次读取的数据有可能会把第1次读取的数据给覆盖掉
		{
		   baos.write(buffer,0,len);
		}
		
		byte[] data=http://www.mamicode.com/baos.toByteArray();//得到内存中的数据 以二进制存放的>
FileServiceTest.java(测认单元类)
package com.example.l3_files.model;

import java.io.IOException;


import android.test.AndroidTestCase;

public class FileServiceTest extends AndroidTestCase {  //测试单元
	public void testSave() throws IOException {
		FileService fileService=new FileService(getContext());
		fileService.save("file1.txt", "保存测试");
	}
	public void testReadFile() throws IOException {
		FileService fileService=new FileService(getContext());
    	String content=fileService.readFile("file1.txt");
        System.out.println(content);
	}

}

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

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/filename" />

    <EditText
        android:id="@+id/filename"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" />

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/filecontent" />

    <EditText
        android:id="@+id/filecontent"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="top"
        android:minLines="5" />

    <Button
        android:id="@+id/save"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/save" />

</LinearLayout>



测试类的使用：
右键已编写的测试方法，Run as->Android JUnit  Test.

如下测试成功，如果Errors不为0，则测试失败。