public class ExitUtil {  public static final int EXIT_APPLICATION = 0x0001;  private Context mContext;  public ExitUtil(Context context) {   mContext = context;  }  // 完全退出应用程序  public void exit() {   Intent intent = new Intent(mContext, MainActivity.class);   // 设置FLAG!!!表示从当前Activity跳转到intent构造方法中添加的类，并且把两个Activity之间的Activity给finish掉！   intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);   // 发出退出应用程序指示   intent.putExtra("flag", EXIT_APPLICATION);   mContext.startActivity(intent);  } }

public class BActivity extends Activity {  private static final int MENU_EXITAPPLICATION = Menu.FIRST;  @Override  protected void onCreate(Bundle savedInstanceState) {   super.onCreate(savedInstanceState);   TextView tv = new TextView(this);   tv.setText("wecolme!");   setContentView(tv);  }  @Override  public boolean onCreateOptionsMenu(Menu menu) {   menu.add(0, MENU_EXITAPPLICATION, 0, "退出程序");   return super.onCreateOptionsMenu(menu);  }  @Override  public boolean onOptionsItemSelected(MenuItem item) {   // 其它Activity调用程序就通过此方法   if (item.getItemId() == MENU_EXITAPPLICATION) {    ExitUtil eu = new ExitUtil(this);    eu.exit();   }   return super.onOptionsItemSelected(item);  } }

public class MainActivity extends Activity {  Button btn = null;  @Override  protected void onCreate(Bundle savedInstanceState) {   super.onCreate(savedInstanceState);   setContentView(R.layout.activity_main);   btn = (Button) findViewById(R.id.btn);   btn.setOnClickListener(new OnClickListener() {// 点击进入BActivity    @Override    public void onClick(View v) {     Intent intent = new Intent(getApplicationContext(), BActivity.class);     startActivity(intent);    }   });  }  // 接受退出程序的指令  @Override  protected void onStart() {   int flag = getIntent().getIntExtra("flag", 0);// 第一次,进入应用时获取得到的flag为默认的值0!   if (flag == ExitUtil.EXIT_APPLICATION) {    finish();   }   Log.i("TAG", "Start");   super.onStart();  }  // 当Activity是单例模式的时候，两次启动该Activity就不会调用onCreate->onStart这些方法了  @Override  protected void onNewIntent(Intent intent) {   int flag = getIntent().getIntExtra("flag", 0);   if (flag == ExitUtil.EXIT_APPLICATION) {    finish();   }   Log.i("TAG", "NewIntent");   super.onNewIntent(intent);  } }