In this tutorial, we will learn to create a "Hello User" application. Users can enter a text into the textbox, then click the button. The application will get the value from the textbox and display the hello message on the screen. The application will also print out the current time and date.

Objective

Object-Oriented programming is the most current way of programming. The concept of OO is now applied to not only programming, but also database system, interactive interface, application structure, and various areas. This tutorial will help students to understand how OOP works, how convenient the OOP is! Students will easily start to get into the concept of OO programming and use it for future programming.

Software Requirement

ü Java JDK, JRE 1.7 or newer

ü Android Studio 2.2.3

Tutorial

MainActivity.java

package com.example.helloworld;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;

import android.view.View;

import android.widget.Button;

import android.widget.EditText;

import android.widget.TextView;

import java.text.DateFormat;

import java.util.Date;

public class MainActivity extends AppCompatActivity {

Button btnGreeting;

TextView txtGreeting;

EditText editTextName;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

btnGreeting = (Button) findViewById(R.id.btnGreeting);

txtGreeting = (TextView) findViewById(R.id.txtGreeting);

editTextName = (EditText) findViewById(R.id.editTextTextPersonName);

btnGreeting.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View v) {

String currentDateTimeString = DateFormat.getDateInstance().format(new Date());

String name = editTextName.getText().toString();

txtGreeting.setText("Hello " + name + "!\n"+ "Today is: " + currentDateTimeString);

}

});

}

}

activity_main.xml

<?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:layout_marginLeft="10dp"

tools:context=".MainActivity"

android:layout_marginStart="10dp">

<TextView

android:id="@+id/txtGreeting"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_marginTop="20dp"

android:layout_marginStart="10dp"

android:text="Hello World!"

app:layout_constraintLeft_toLeftOf="parent"

app:layout_constraintTop_toBottomOf="@+id/btnGreeting"

android:layout_marginLeft="10dp" />

<Button

android:id="@+id/btnGreeting"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_marginTop="20dp"

android:text="Greeting"

app:layout_constraintStart_toStartOf="parent"

app:layout_constraintTop_toBottomOf="@+id/editTextTextPersonName" />

<EditText

android:id="@+id/editTextTextPersonName"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:ems="10"

android:inputType="textPersonName"

android:hint="Please enter you name"

app:layout_constraintStart_toStartOf="parent"

app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

initial interface