JAVA事件处理：画一个变色圆

要求描述

• 界面如下图所示

• 当点击不同的按钮时,圆的填充颜色会随之改变

• 用鼠标点击圆内部时,圆的 填充颜色会依照”面板背景色-红色-绿色-蓝色”循环改变

• 鼠标移到圆内时,光标变成十字形

效果展示

代码部分

package backage7;

import javax.swing.*;
import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;

public class ColorChangingCircle extends JFrame {

    private Color[] colors = {null, Color.RED, Color.GREEN, Color.BLUE};
    private int currentColorIndex = 0;

    public ColorChangingCircle() {
        setTitle("ColorChangingCircle");
        setSize(400, 400);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);

        JButton redButton = new JButton("Red");
        JButton greenButton = new JButton("Green");
        JButton blueButton = new JButton("Blue");

        redButton.addActionListener(e -> changeColor(Color.RED));
        greenButton.addActionListener(e -> changeColor(Color.GREEN));
        blueButton.addActionListener(e -> changeColor(Color.BLUE));

        JPanel buttonPanel = new JPanel();
        buttonPanel.add(redButton);
        buttonPanel.add(greenButton);
        buttonPanel.add(blueButton);

        JPanel circlePanel = new JPanel() {
            @Override
            protected void paintComponent(Graphics g) {
                super.paintComponent(g);
                if (colors[currentColorIndex] != null) {
                    g.setColor(colors[currentColorIndex]);
                    int diameter = 200;
                    g.fillOval(getWidth() / 2 - diameter / 2, getHeight() / 2 - diameter / 2, diameter, diameter);
                } else {
                    g.setColor(Color.BLACK);
                    int diameter = 200;
                    g.drawOval(getWidth() / 2 - diameter / 2, getHeight() / 2 - diameter / 2, diameter, diameter);
                }
            }
        };

        circlePanel.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {
                if (isMouseInsideCircle(e)) {
                    cycleColors();
                    circlePanel.repaint();
                }
            }
        });

        circlePanel.addMouseMotionListener(new MouseMotionAdapter() {
            @Override
            public void mouseMoved(MouseEvent e) {
                if (isMouseInsideCircle(e)) {
                    setCursor(Cursor.getPredefinedCursor(Cursor.CROSSHAIR_CURSOR));
                } else {
                    setCursor(Cursor.getDefaultCursor());
                }
            }
        });

        setLayout(new BorderLayout());
        add(buttonPanel, BorderLayout.NORTH);
        add(circlePanel, BorderLayout.CENTER);

        setVisible(true);
    }

    private void changeColor(Color color) {
        currentColorIndex = indexOfColor(color);
        repaint();
    }

    private void cycleColors() {
        currentColorIndex = (currentColorIndex + 1) % colors.length;
    }

    private int indexOfColor(Color color) {
        for (int i = 0; i < colors.length; i++) {
            if ((colors[i] == null && color == null) || (colors[i] != null && colors[i].equals(color))) {
                return i;
            }
        }
        return -1;
    }

    private boolean isMouseInsideCircle(MouseEvent e) {
        int mouseX = e.getX();
        int mouseY = e.getY();
        int circleX = getWidth() / 2;
        int circleY = getHeight() / 2 - 35;
        int radius = 100; // 半径为圆的直径的一半
        return Math.pow(mouseX - circleX, 2) + Math.pow(mouseY - circleY, 2) <= Math.pow(radius, 2);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(ColorChangingCircle::new);
    }
}