Android กับ setContentView() ควบคุมการแสดงผล XML Layout ของแต่ล่ะ Activity

package com.myapp;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.app.Activity;

public class MainActivity extends Activity {

	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		
		// Default Show ShowConventView1()
		ShowConventView1();
        
	}
	
	// Show activity_main.xml
	public void ShowConventView1()
	{
		setContentView(R.layout.activity_main);

		// Button1
        final Button btn1 = (Button) findViewById(R.id.button1);
        // Perform action on click
        btn1.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
            	ShowConventView2();
            }
        });
	}
	
	// Show activity_form2.xml
	public void ShowConventView2()
	{
     	setContentView(R.layout.activity_form2); // Show activity_form2
     	
     	// Button2
        final Button btn2 = (Button) findViewById(R.id.button2);
        // Perform action on click
        btn2.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
            	ShowConventView3();
            }
        });
	}
	
	// Show activity_form3.xml
	public void ShowConventView3()
	{
     	setContentView(R.layout.activity_form3); // Show activity_form3
     	
     	// Button3
        final Button btn3 = (Button) findViewById(R.id.button3);
        // Perform action on click
        btn3.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
            	ShowConventView1();
            }
        });
	}

}

		setContentView(R.layout.activity_main);