AlertDialog in Android

Today I am going  to demonstrate how to use alert dialog box in android. I have created a demo project named alertDemo. In this project on the launch of application alert box will come asking you to continue with the application with having Yes and No buttons. On the tap of buttons desired functionality happen.
Step 1:- MainActivity.java
package com.arpit.alertdemo;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.DialogInterface.OnClickListener;
import android.os.Bundle;
import android.view.Menu;
public class MainActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // settin up an alert
       
        AlertDialog.Builder alert = new AlertDialog.Builder(
                MainActivity.this);
        // set title for the alert
        alert.setTitle("AlertDemo");
        // set message
        alert.setMessage("Do you want to continue with the application?");
        alert.setPositiveButton("YES", new OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                // TODO Auto-generated method stub
                   
                dialog.dismiss();   
                       
            }
        });
        alert.setNegativeButton("CANCEL", new OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                // TODO Auto-generated method stub
                finish();
            }
        });
       
       
        alert.show();
       
        setContentView(R.layout.activity_main);
    }
    @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;
    }
}
Step 2:-  activity_mai.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />
</RelativeLayout>