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);