dynamic widgets exchanging

main_activity.xml

<LinearLayout id="@+id/linearLayout">
  <Button id="@+id/button1"/>
  <Button id="@+id/button2"/>
  <Button id="@+id/button3"/>
  <Button id="@+id/button4"/>
</LinearLayout>

MainActivity.java

public class MainActivity extends Activity {
	//  @see main_activity.xml
	ViewGroup linearLayout1 = null;
	Button button1 = null;
	Button button2 = null;
	Button button3 = null;
	Button button4 = null;
	
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		// find container widget
		linearLayout1 = (ViewGroup)findViewById(R.id.linearLayout1);
		// find each buttons
		button1 = (Button)findViewById(R.id.button1);
		button2 = (Button)findViewById(R.id.button2);
		button3 = (Button)findViewById(R.id.button3);
		button4 = (Button)findViewById(R.id.button4);
		changeState(0);
		//
		// ...
		//
	}
	private changeState(int state) {
		linearLayout1.removeAllViews();
		switch(state) {
		case 0:
			linearLayout1.addView(button1);
			linearLayout1.addView(button2);
			break;
		case 1:
			linearLayout1.addView(button3);
			linearLayout1.addView(button4);
			break;
		}
		//
		// ...
		//
	}
}