Android 추가 단추 이벤트 응답

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class MainActivity extends Activity {

	
	OnClickListener listener1 = null;
	OnClickListener listener2 = null;
	OnClickListener listener3 = null;
	
	Button button1;
	Button button2;
	Button button3;
	
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
       
        
        listener1 =new  OnClickListener(){
        	public void onClick(View v){
        		Intent intent1 = new Intent(MainActivity.this ,OneActivity.class);
        		startActivity(intent1);
        	}
        };
        listener2 = new OnClickListener(){
			
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				Intent intent2 =  new Intent(MainActivity.this,TwoActivity.class);
				startActivity(intent2);
				}
		};
        listener3 = new OnClickListener() {
			
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				Intent intent3 = new Intent(MainActivity.this,ThreeActivity.class);
				startActivity(intent3);
			}
		};
        
        setContentView(R.layout.activity_main);
        button1 = (Button)findViewById(R.id.buttonOne);
        button1.setOnClickListener(listener1);
        button2 =(Button)findViewById(R.id.buttonTwo);
        button2.setOnClickListener(listener2);
        button3 = (Button)findViewById(R.id.buttonThree);
        button3.setOnClickListener(listener3);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }
    
}