ยืนยันการออกจากแอปพลิเคชัน เมื่อกดปุ่ม Back ใน Android app

public void onBackPressed() {
    // กดปุ่ม Back แล้วจะให้โปรแกรมทำอะไรให้ใส่ในนี้
}

AlertDialog.Builder dialog = new AlertDialog.Builder(this);
dialog.setTitle("Exit");
dialog.setIcon(R.drawable.ic_launcher);
dialog.setCancelable(true);
dialog.setMessage("Do you want to exit?");

dialog.setPositiveButton("Yes", new OnClickListener() {
    public void onClick(DialogInterface dialog, int which) {
        finish();
    }    
});

dialog.setNegativeButton("No", new OnClickListener() {
    public void onClick(DialogInterface dialog, int which) {
        dialog.cancel();
    }
});
        
dialog.show();  

package app.akexorcist.dialogclosewarning;

import android.os.Bundle;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.DialogInterface.OnClickListener;

public class Main extends Activity {

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }
    
    public void onBackPressed() {
        AlertDialog.Builder dialog = new AlertDialog.Builder(this);
        dialog.setTitle("Exit");
        dialog.setIcon(R.drawable.ic_launcher);
        dialog.setCancelable(true);
        dialog.setMessage("Do you want to exit?");
        dialog.setPositiveButton("Yes", new OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                finish();
            }
        });
        
        dialog.setNegativeButton("No", new OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                dialog.cancel();
            }
        });
        
        dialog.show();                
    }
}

<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" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />

</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="app.akexorcist.dialogclosewarning"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="19" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="app.akexorcist.dialogclosewarning.Main"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>