Android - Resume an activity from other application

I have two apps A(activity A1, A2, A3) and B(activity B1, B2). My process like this:

A1 -> A2 -> A3 -> B1 -> B2

My question is: from activity B2, how to resume to the existed activity A3 - no creating a new activity A3 - like switching 2 applications by using multi-task button?

Thanks,

You need singleTop to make the activity always use the same instance, then in that activity onNewIntent will be triggered whenever we return there from another activity (via intent)

<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="..." >
<application ...>
    <!-- android:launchMode="singleTop" makes sure we reuse the same instance -->
    <activity android:name=".A3Activity" android:label="@string/app_name"
        android:launchMode="singleTop">...</activity>
    ...
</application>


public class A3Activity extends Activity {
    @Override
    protected void onNewIntent(Intent intent) {
        //This is triggered onyl when re-launched
        super.onNewIntent(intent);
        //do anything new here
    }
}

public class B2Activity extends Activity {

    public void someMethod() {
        //This relaunches the A3 activity from same app
        //Intent intent = new Intent(this, A3Activity.class);

        //This does it from the other app
        Intent intent = new Intent(
        intent.setComponent(new ComponentName("com.anh", "com.anh.A3Activity"));
        startActivity(intent);
    } 

}