public class Activity extends ContextThemeWrapper implements LayoutInflater.Factory2,Window.Callback, KeyEvent.Callback,OnCreateContextMenuListener, ComponentCallbacks2,Window.OnWindowDismissedCallback, WindowControllerCallback,AutofillManager.AutofillClientpublic abstract class Service extends ContextWrapper implements ComponentCallbacks2 *****public class ContextThemeWrapper extends ContextWrapper从activity和service看出来，它们都继承自context实现不同的接口，实现决定了它们的功能．

package com.example.oneactivity;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.Button;public class OneMainActivity extends Activity {Button button;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_one_main);button = (Button)findViewById(R.id.button);button.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View arg0) {// TODO Auto-generated method stubIntent intent = new Intent();intent.setAction("com.ysfl.otherActivity");//此处设置需要起动app的action.Log.d(this.getClass().getName(),"I'm OneMainActivity onclick to start anotherActivity");startActivity(intent);//跨进程调用其它应用}});}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {// Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.activity_one_main, menu);return true;}@Overrideprotected void onPause(){super.onPause();Log.d(this.getClass().getName(),"I'm OneMainActivity  onPause");}@Overrideprotected void onStop(){super.onStop();Log.d(this.getClass().getName(),"I'm OneMainActivity  onStop");}@Overrideprotected void onDestroy(){super.onDestroy();Log.d(this.getClass().getName(),"I'm OneMainActivity  onDestroy");}
}

package com.example.anotheractivity;import android.os.Bundle;
import android.app.Activity;
import android.util.Log;
import android.view.Menu;
import android.widget.Toast;public class AnotherMainActivity extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_another_main);Log.d(this.getClass().getName(),"I'm AnotherMainActivity  onCreate");}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {// Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.activity_another_main, menu);return true;}@Overrideprotected void onPause(){super.onPause();Log.d(this.getClass().getName(),"I'm AnotherMainActivity  onPause");}@Overrideprotected void onStop(){super.onStop();Log.d(this.getClass().getName(),"I'm AnotherMainActivity  onStop");}@Overrideprotected void onDestroy(){super.onDestroy();Log.d(this.getClass().getName(),"I'm AnotherMainActivity  onDestroy");}
}

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"package="com.example.anotheractivity"android:versionCode="1"android:versionName="1.0" ><uses-sdkandroid:minSdkVersion="8"android:targetSdkVersion="17" /><applicationandroid:allowBackup="true"android:icon="@drawable/ic_launcher"android:label="@string/app_name"android:theme="@style/AppTheme" ><activityandroid:name="com.example.anotheractivity.AnotherMainActivity"android:label="@string/app_name" ><intent-filter>              <!-- 此处的action是其它应用需要起动的action --><action android:name="com.ysfl.otherActivity" /><category android:name="android.intent.category.DEFAULT" /><action android:name="android.intent.action.MAIN" /><category android:name="android.intent.category.LAUNCHER" /></intent-filter></activity></application>
</manifest>