如何在Java GUI中使用计时器重复更改圆圈的颜色? [英] How to repeatedly change colors of a circle using a timer in a Java GUI?

问题描述

我正在尝试使用Java GUI创建交通灯，其中它仅显示一个圆圈，并且将颜色从红色，黄色更改为绿色.应该有一个计时器，并且三秒钟之内只有黄色会变成绿色.我已经设置了一个圆圈和一个红色，但是我无法使用计时器将其分别更改为黄色和绿色.

I am trying to create a traffic light using a Java GUI, where it displays only one circle and it changes colours from red, to yellow, to green. There should be a timer and only yellow should be changing to green within 3 seconds. I have set up a circle and a colour red, but I am unable to change it to the colours yellow, and green respectively using a timer.

顺便说一句，我确实是GUI的新手，虽然我仍然观看了一些youtube视频，但没有发现任何有用的信息或与此任务相关的信息，但我在网上找不到有用的资源.任何帮助将不胜感激！

代码:

import java.awt.Canvas;
import java.awt.Graphics;
import java.awt.Color;
import javax.swing.JFrame;

public class Main extends Canvas {
public static void main(String[] args) {
    JFrame frame = new JFrame();
    Canvas canvas = new Main();
    canvas.setSize(700, 700);
    frame.add(canvas);
    frame.pack();
    frame.setVisible(true);
}

public void paint(Graphics g) {
    g.setColor(Color.red);
    g.fillOval(200, 200, 300, 300);
   }
}

预期输出:

https://www.youtube.com/watch?v=8dn-_3t3XQE

注意:它只能是一个圆圈，但其行为应与预期输出中的一个圆圈相同.

推荐答案

这是一种方法.指示灯保持亮起3秒钟.要更改其持续时间，必须相应地修改代码.这将在计时器内部完成.

Here is one approach. The lights stay on for 3 seconds. To change their duration the code must be modified accordingly. This would be done inside the timer.

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;

public class TrafficLight extends JPanel {
    JFrame frame = new JFrame();
    
    int colorIdx = 0;
    Color[] colors = { Color.green, Color.yellow, Color.red };
    
    public static void main(String[] args) {
        // Ensure the program is started on the Event Dispatch Thread
        SwingUtilities.invokeLater(() -> new TrafficLight().start());
    }
    
    public void start() {
        // set up
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        // set the preferred size. Okay in this instance but best
        // practice dictates to override getPreferredSize()
        setPreferredSize(new Dimension(500, 500));
        
        frame.add(this);
        frame.pack();
        
        // center on screen
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
        
        Timer t = new Timer(3000, ae -> {
            colorIdx = colorIdx >= 2 ? 0 : colorIdx + 1;
            repaint();
        });
        t.start();
    }
    
    
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        
        g.setColor(colors[colorIdx]);
        g.fillOval(150, 150, 200, 200);
        
    }
    
}

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