PROGRAM 9:
XML CODE:
<?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"
 tools:context=".MainActivity">
 <TextView
 android:id="@+id/messageTextView"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:text="No messages yet"
 android:layout_centerHorizontal="true"
 android:layout_marginTop="50dp"
 android:textSize="18sp" />
 <Button
 android:id="@+id/receiveMessageButton"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:text="Receive Message"
 android:layout_below="@id/messageTextView"
 android:layout_centerHorizontal="true"
 android:layout_marginTop="20dp" />
</LinearLayout>
JAVA CODE:
package com.example.program9;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.app.AlertDialog;
import android.content.DialogInterface;
public class MainActivity extends AppCompatActivity {
 private TextView messageTextView;
 private Button receiveMessageButton;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 messageTextView = findViewById(R.id.messageTextView);
 receiveMessageButton = findViewById(R.id.receiveMessageButton);
 receiveMessageButton.setOnClickListener(new
View.OnClickListener() {
 @Override
 public void onClick(View v) {
 String message = "You have received a new message!";
 messageTextView.setText(message);
 new AlertDialog.Builder(MainActivity.this)
 .setTitle("New Message")
 .setMessage(message)
 .setPositiveButton("OK", new
 DialogInterface.OnClickListener() {
 @Override
 public void onClick(DialogInterface dialog, int which)
{
 dialog.dismiss(); }
 })
 .show();
 } }); }}