AlertDialogBox

 It is display the some alert
  Using Builder class

activitymain.xml :-

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
  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:orientation="vertical"
  tools:context="com.kiranapp.MainActivity">
<Button
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:id="@+id/button"
  android:layout_gravity="center_horizontal"
  android:text="Alertdialog"
  android:layout_marginTop="20dp" />
</LinearLayout>

MainActivity.java :-

package com.kiranapp;

import android.content.DialogInterface;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
 Button alertbtn;

@Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 alertbtn=(Button)findViewById(R.id.button);
 alertbtn.setOnClickListener(new View.OnClickListener() {
@Override
  public void onClick(View v) {

AlertDialog.Builder builder=new AlertDialog.Builder(MainActivity.this);
 builder.setTitle("Alert?");
 builder.setMessage("Hello do u want to close the app");
 builder.setIcon(R.mipmap.ic_launcher);
 builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
@Override
  public void onClick(DialogInterface dialog, int which) {
  finish();
 Toast.makeText(MainActivity.this, "App Closed", Toast.LENGTH_SHORT).show();
  }
 });
builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
@Override
  public void onClick(DialogInterface dialog, int which) {
 Toast.makeText(MainActivity.this, "Dialog is CLosed", Toast.LENGTH_SHORT).show();
  }
 });
 builder.create();
 builder.show();
 }
});
}
}

Output :-

AlertDialogBox fig :1

AlertDialogBox fig :2