Java· swing 小demo

简单的 Java Swing 画图 Demo，包含基本的绘图功能（直线、矩形、椭圆）和颜色选择功能。这个示例代码结构清晰，适合初学者理解 Swing 绘图的基本原理

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.ArrayList;

public class SimpleDrawingDemo {
    public static void main(String[] args) {
        // 创建并设置GUI
        JFrame frame = new JFrame("简易绘图工具");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(800, 600);
        
        // 创建绘图面板
        DrawingPanel drawingPanel = new DrawingPanel();
        
        // 创建工具栏
        JPanel toolPanel = new JPanel();
        JButton lineBtn = new JButton("直线");
        JButton rectBtn = new JButton("矩形");
        JButton ovalBtn = new JButton("椭圆");
        JButton clearBtn = new JButton("清除");
        
        // 添加按钮到工具栏
        toolPanel.add(lineBtn);
        toolPanel.add(rectBtn);
        toolPanel.add(ovalBtn);
        toolPanel.add(clearBtn);
        
        // 添加颜色选择器
        JButton colorBtn = new JButton("颜色");
        toolPanel.add(colorBtn);
        
        // 按钮事件监听
        lineBtn.addActionListener(e -> drawingPanel.setShapeType(ShapeType.LINE));
        rectBtn.addActionListener(e -> drawingPanel.setShapeType(ShapeType.RECTANGLE));
        ovalBtn.addActionListener(e -> drawingPanel.setShapeType(ShapeType.OVAL));
        clearBtn.addActionListener(e -> drawingPanel.clear());
        
        // 颜色选择事件
        colorBtn.addActionListener(e -> {
            Color newColor = JColorChooser.showDialog(frame, "选择颜色", drawingPanel.getColor());
            if (newColor != null) {
                drawingPanel.setColor(newColor);
            }
        });
        
        // 添加组件到窗口
        frame.add(toolPanel, BorderLayout.NORTH);
        frame.add(drawingPanel, BorderLayout.CENTER);
        
        // 显示窗口
        frame.setVisible(true);
    }
}

// 绘图形状枚举
enum ShapeType {
    LINE, RECTANGLE, OVAL
}

// 绘图形状类
class Shape {
    private int x1, y1, x2, y2;
    private Color color;
    private ShapeType type;
    
    public Shape(int x1, int y1, int x2, int y2, Color color, ShapeType type) {
        this.x1 = x1;
        this.y1 = y1;
        this.x2 = x2;
        this.y2 = y2;
        this.color = color;
        this.type = type;
    }
    
    public void draw(Graphics g) {
        g.setColor(color);
        switch (type) {
            case LINE:
                g.drawLine(x1, y1, x2, y2);
                break;
            case RECTANGLE:
                g.drawRect(Math.min(x1, x2), Math.min(y1, y2), 
                           Math.abs(x2 - x1), Math.abs(y2 - y1));
                break;
            case OVAL:
                g.drawOval(Math.min(x1, x2), Math.min(y1, y2), 
                          Math.abs(x2 - x1), Math.abs(y2 - y1));
                break;
        }
    }
}

// 绘图面板类
class DrawingPanel extends JPanel {
    private ArrayList<Shape> shapes = new ArrayList<>();
    private ShapeType currentShapeType = ShapeType.LINE;
    private Color currentColor = Color.BLACK;
    private int startX, startY;
    private Shape currentShape;
    
    public DrawingPanel() {
        setBackground(Color.WHITE);
        
        // 添加鼠标监听器
        addMouseListener(new MouseAdapter() {
            @Override
            public void mousePressed(MouseEvent e) {
                startX = e.getX();
                startY = e.getY();
            }
            
            @Override
            public void mouseReleased(MouseEvent e) {
                int endX = e.getX();
                int endY = e.getY();
                shapes.add(new Shape(startX, startY, endX, endY, currentColor, currentShapeType));
                repaint();
            }
        });
        
        // 添加鼠标移动监听器
        addMouseMotionListener(new MouseMotionAdapter() {
            @Override
            public void mouseDragged(MouseEvent e) {
                int endX = e.getX();
                int endY = e.getY();
                currentShape = new Shape(startX, startY, endX, endY, currentColor, currentShapeType);
                repaint();
            }
        });
    }
    
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        
        // 绘制所有已保存的形状
        for (Shape shape : shapes) {
            shape.draw(g);
        }
        
        // 绘制当前正在绘制的形状
        if (currentShape != null) {
            currentShape.draw(g);
        }
    }
    
    public void setShapeType(ShapeType type) {
        this.currentShapeType = type;
    }
    
    public void setColor(Color color) {
        this.currentColor = color;
    }
    
    public Color getColor() {
        return currentColor;
    }
    
    public void clear() {
        shapes.clear();
        repaint();
    }
}

代码功能说明：

1. 主窗口（SimpleDrawingDemo）：创建窗口和工具栏，添加各种绘图工具按钮。
2. 绘图面板（DrawingPanel）：核心绘图区域，处理鼠标事件和图形绘制。
3. 形状类（Shape）：封装绘图形状的属性（位置、颜色、类型）和绘制方法。
4. 形状类型枚举（ShapeType）：定义支持的绘图形状类型（直线、矩形、椭圆）。

使用方法：

1. 选择绘图工具（直线、矩形、椭圆）。
2. 点击 "颜色" 按钮选择绘图颜色。
3. 在白色区域按住鼠标左键并拖动进行绘图。
4. 点击 "清除" 按钮可以清空画布。

这个 Demo 包含了 Swing 绘图的基本要素：鼠标事件处理、图形绘制、组件布局等。你可以在此基础上添加更多功能，如填充颜色、线条粗细调整、撤销操作等