在Activity中封闭另一个Activity

在Activity中关闭另一个Activity
1.对于简单的两个Activity

public class A_activity extends Activity {

      public static A_activity _instance = null;

         @Override
         protected void onCreate(Bundle savedInstanceState) {
               // TODO Auto-generated method stub
               super.onCreate(savedInstanceState);
                .....
              _instance = this;
         }

   }

  public class B_activity extends Activity {

          @Override
         protected void onCreate(Bundle savedInstanceState) {
                  // TODO Auto-generated method stub
                super.onCreate(savedInstanceState);
                A_activity._instance.finish();
          }
   }

2.也可以通过ActivityManager

ActivityManager manager = (ActivityManager)getSystemService(ACTIVITY_SERVICE);  
manager.restartPackage(packageName);