java实现绘制空心半圆，空心圆形，空心矩形 ，空心三角形，空心梯形

可以使用Java的Graphics2D类来绘制空心图形。下面是一些例子：

1. 空心半圆：

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.Arc2D;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class HalfCircle extends JPanel {
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        int width = getWidth();
        int height = getHeight();
        Arc2D.Float arc = new Arc2D.Float(0, 0, width, height, 0, 180, Arc2D.OPEN);
        g2d.draw(arc);
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("Half Circle");
        frame.add(new HalfCircle());
        frame.setSize(300, 300);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}

2. 空心圆形：

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.Ellipse2D;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Circle extends JPanel {
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        int width = getWidth();
        int height = getHeight();
        Ellipse2D.Float ellipse = new Ellipse2D.Float(0, 0, width, height);
        g2d.draw(ellipse);
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("Circle");
        frame.add(new Circle());
        frame.setSize(300, 300);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}

3. 空心矩形：

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.Rectangle2D;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Rectangle extends JPanel {
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        int width = getWidth();
        int height = getHeight();
        Rectangle2D.Float rectangle = new Rectangle2D.Float(0, 0, width, height);
        g2d.draw(rectangle);
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("Rectangle");
        frame.add(new Rectangle());
        frame.setSize(300, 300);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}

4. 空心三角形：

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Polygon;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Triangle extends JPanel {
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        int width = getWidth();
        int height = getHeight();
        int[] xPoints = {0, width / 2, width};
        int[] yPoints = {height, 0, height};
        Polygon triangle = new Polygon(xPoints, yPoints, 3);
        g2d.draw(triangle);
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("Triangle");
        frame.add(new Triangle());
        frame.setSize(300, 300);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}

5. 空心梯形：

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Polygon;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Trapezoid extends JPanel {
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        int width = getWidth();
        int height = getHeight();
        int[] xPoints = {width / 4, 3 * width / 4, width, 0};
        int[] yPoints = {0, 0, height, height};
        Polygon trapezoid = new Polygon(xPoints, yPoints, 4);
        g2d.draw(trapezoid);
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("Trapezoid");
        frame.add(new Trapezoid());
        frame.setSize(300, 300);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}