Javaで時計アプリを作ろう｜初心者向けGUI×リアルタイム表示の完全解説

"I want to make something with Java, but I can't think of a practical application."
"I want to try making an app that works in real time."
For those who have such concerns, we recommendCreating a Clock Appis.

In JavaA simple class and GUI combinationYou can then create an app that displays the current time in real time.
Even beginners can enjoy learning how to get the time and update the display.It's the subject.

In this article, we will show you how anyone can make it.Detailed explanation with easy-to-understand codeWe will continue to do so.

table of contents

What is the point of creating a clock app?
1. Why are clock apps great for learning?
How to Get the Current Time in Java
1. How to use LocalTime and DateTimeFormatter
How to display the current time in a GUI
1. Steps to display on the screen using Swing
How to update every second with a Timer
1. Update the time every second with javax.swing.Timer
Completed code for the Java clock app
What to do when it doesn't work properly
1. Common mistakes and how to fix them
Application ideas and step-up
1. Examples of features we would like to try next
Summary and configuration of the completed code
Summary: The next step in learning Java

What is the point of creating a clock app?

Why are clock apps great for learning?

Conclusion: Because you can learn the basics of real-time processing and GUI updates at the same time.

The next step for Java beginners is to:
It makes a lot of sense to create an app that runs in real time.

What you'll learn by building a clock app:

Get the current time (LocalTimeclass, etc.)
Looping and waiting (Timer(How to use, etc.)
Swing GUI display and update

For example, the Ministry of Education, Culture, Sports, Science and Technology's "Development of Information Utilization Skills"
Emphasis on "developing computational thinking by linking it to real life"It has been
(Reference: https://www.mext.go.jp/a_menu/shotou/zyouhou/detail/1375607.htm).

The clock app is the gatewayThe perfect subjectis.

How to Get the Current Time in Java

How to use LocalTime and DateTimeFormatter

Conclusion: Java 8 and abovejava.timeThis can be easily achieved using the package.

import java.time.LocalTime; import java.time.format.DateTimeFormatter; LocalTime now = LocalTime.now(); String time = now.format(DateTimeFormatter.ofPattern("HH:mm:ss"));

With this code, you can always get the latesthours: minutes: secondsYou can get the time as a string.

How to display the current time in a GUI

Steps to display on the screen using Swing

Conclusion:JLabelYou can set it to a time string and display it on the screen.

First, the basic label:

1	`JLabel label =` `new` `JLabel("Current time: 00:00:00"); frame.add(label);`

and,How the time is updated every secondAs,javax.swing.TimerUse.

How to update every second with a Timer

Update the time every second with javax.swing.Timer

In conclusion, you can use a Timer to set up periodic event processing.

Below is the code for updating using a Timer.

Timer timer = new Timer(1000, new ActionListener() { public void actionPerformed(ActionEvent e) { LocalTime now = LocalTime.now(); String time = now.format(DateTimeFormatter.ofPattern("HH:mm:ss")); label.setText("Current time:" + time); } }); timer.start();

This will update the screen every second.A real-time clockIt will be.

Completed code for the Java clock app

import javax.swing.*; import java.awt.*; import java.awt.event.*; import java.time.LocalTime; import java.time.format.DateTimeFormatter; public class ClockApp extends JFrame { private JLabel label; public ClockApp() { label = new JLabel(); label.setFont(new Font("Arial", Font.BOLD, 32)); label.setHorizontalAlignment(SwingConstants.CENTER); getContentPane().add(label); setTitle("Clock app"); setSize(300, 150); setDefaultCloseOperation(EXIT_ON_CLOSE); setVisible(true); Timer timer = new Timer(1000, new ActionListener() { public void actionPerformed(ActionEvent e) { LocalTime now = LocalTime.now(); String time = now.format(DateTimeFormatter.ofPattern("HH:mm:ss")); label.setText(time); } }); timer.start(); } public static void main(String[] args) { new ClockApp(); } }