<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/white"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Press The Back Button of Your Phone."
        android:textSize="24sp"
        android:textStyle="bold"
        android:textAlignment="center"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

import android.content.DialogInterface;
import android.os.Bundle;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity 
{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    // Declare the onBackPressed method when the
    // back button is pressed this method will call
    @Override
    public void onBackPressed() {
        
        // Create the object of AlertDialog Builder class
        AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);

        // Set the message show for the Alert time
        builder.setMessage("Do you want to exit ?");

        // Set Alert Title
        builder.setTitle("Alert !");

        // Set Cancelable false for when the user clicks
        // on the outside the Dialog Box then it will remain show
        builder.setCancelable(false);

        // Set the positive button with yes name Lambda
        // OnClickListener method is use of DialogInterface interface.
        builder.setPositiveButton("Yes", (DialogInterface.OnClickListener) (dialog, which) -> {
            
            // When the user click yes button then app will close
            finish();
        });

        // Set the Negative button with No name Lambda
        // OnClickListener method is use of DialogInterface interface.
        builder.setNegativeButton("No", (DialogInterface.OnClickListener) (dialog, which) -> {
            
            // If user click no then dialog box is canceled.
            dialog.cancel();
        });

        // Create the Alert dialog
        AlertDialog alertDialog = builder.create();
        
        // Show the Alert Dialog box
        alertDialog.show();
    }
}

import android.os.Bundle
import androidx.appcompat.app.AlertDialog
import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() 
{
    override fun onCreate(savedInstanceState: Bundle?) 
    {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }

    // Declare the onBackPressed method when the back
    // button is pressed this method will call
    override fun onBackPressed() {
        
        // Create the object of AlertDialog Builder class
        val builder = AlertDialog.Builder(this)

        // Set the message show for the Alert time
        builder.setMessage("Do you want to exit ?")

        // Set Alert Title
        builder.setTitle("Alert !")

        // Set Cancelable false for when the user clicks
        // on the outside the Dialog Box then it will remain show
        builder.setCancelable(false)

        // Set the positive button with yes name Lambda
        // OnClickListener method is use of DialogInterface interface.
        builder.setPositiveButton("Yes") {
            
            // When the user click yes button then app will close 
                dialog, which -> finish()
        }

        // Set the Negative button with No name Lambda
        // OnClickListener method is use of DialogInterface interface.
        builder.setNegativeButton("No") {
        
            // If user click no then dialog box is canceled.    
                dialog, which -> dialog.cancel()
        }

        // Create the Alert dialog
        val alertDialog = builder.create()
        
        // Show the Alert Dialog box
        alertDialog.show()
    }
}