Alert Dialogue can be used to display any message to the user or take user choices for some task . Let's see how we can use it in our code. But before that, we need to have our environment ready.

Pre-requisite:

1. JDK installed if you want to code in Java.

2. Android Studio

Start Coding

1) In the main activity the button will create the alert dialog when it is clicked.

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:orientation="vertical"
    android:padding="20dp"
    tools:context=".MainActivity">

<EditText
    android:id="@+id/name"
    android:hint="Name"
    android:layout_marginTop="100dp"
    android:layout_gravity="center"
    android:gravity="center"
    android:layout_width="match_parent"
    android:layout_height="50dp"/>

<Button
    android:id="@+id/btn"
    android:layout_width="100dp"
    android:layout_height="50dp"
    android:layout_gravity="center"
    android:background="#000000"
    android:textColor="#ffffff"
    android:text="Submit"
     />

</LinearLayout>

2)The setTitle() method will display the message. The dialog interface.dismiss() destroys the dialog. alert.setCanceledOnTouchOutside( false ) dismiss the touch outside. If you are working in different activity , use that class name while creating alertdialog object.

MainActivity.java

package com.example.alertdialogue;

import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;

import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate( savedInstanceState );
        setContentView( R.layout.activity_main );
        final EditText editText=findViewById( R.id.name );
        Button button=findViewById( R.id.btn );

        button.setOnClickListener( new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String name=editText.getText().toString().trim();
                AlertDialog.Builder alertdialog=new AlertDialog.Builder(MainActivity.this);
                alertdialog.setTitle( "Hi "+name+". Welcome to Codengocool " );
                alertdialog.setPositiveButton( "Ok", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialogInterface, int i) {
                        dialogInterface.dismiss();
                        Intent intent=new Intent( MainActivity.this,Second.class );
                        startActivity( intent );
                    }
                } );

                alertdialog.setNegativeButton( "Cancel", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialogInterface, int i) {
                        dialogInterface.dismiss();
                    }
                } );

                AlertDialog alert = alertdialog.create();
                alert.setCanceledOnTouchOutside( false );
                alert.show();
            }
        } );



    }
}

3) Creating a Second activity to show how the positive button works.

activity_second.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:orientation="vertical"
    android:gravity="center"
    tools:context=".Second">
<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    android:text="WElCOME"/>
</LinearLayout>

4)Just displaying a random message in Textview.

Second.java

package com.example.alertdialogue;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;

public class Second extends AppCompatActivity {

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

Output

Resources:

1. javatpoint
2. AlertDialog
3. Dialog