您好，我正在尝试提高 java2D 方面的知识，首先我正在处理绘制多边形。但是，我看不到框架上的多边形。我阅读了一些教程和示例，但正如我所说，我遇到了问题。这是绘制多边形的示例代码；

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Polygon;

import javax.swing.JFrame;

public class jRisk extends JFrame {


    private JFrame mainMap;
    private Polygon poly;

    public jRisk(){

        initComponents();

    }

    private void initComponents(){

        mainMap = new JFrame();
        mainMap.setSize(800, 600);
        mainMap.setResizable(false);

        mainMap.setVisible(true);
        mainMap.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        int xPoly[] = {150,250,325,375,450,275,100};
        int yPoly[] = {150,100,125,225,250,375,300};

        poly = new Polygon(xPoly, yPoly, xPoly.length);

    }

    protected void paintComponent(Graphics g){

        super.paintComponents(g);

        g.setColor(Color.BLUE);
        g.drawPolygon(poly);

    }   

    /**
     * @param args
     */
    public static void main(String[] args) {

        new jRisk();

    }

}

最佳答案

JFrame 没有 paintComponent(Graphics g)方法。添加@Override annotation你会得到一个编译时错误。

1) 使用 JPanel 并覆盖 paintComponent(您可以通过 添加 JPanel 到 JFrame >JFrame#add(..))

2) 覆盖 getPreferredSize() 以返回适合您在 Graphics 对象上绘图的正确 Dimension，否则它们将不会被视为 JPanel没有组件的大小是 0,0

3) 不要在 JFrame 上调用 setSize...而是使用正确的 LayoutManager 和/或覆盖 getPrefferedSize() 并在添加所有组件之后但在将其设置为可见之前调用 JFrame 上的 pack()

4) 阅读 Concurrency in Swing具体关于Event Dispatch Thread

5) watch 类命名方案应以大写字母开头，此后每个新词的首字母均应大写

6) 您还扩展JFrame 并有一个变量JFrame 吗？去掉 extend JFrame 并保留 JFrame 变量，因为我们不想要 2 个 JFrame 并且扩展 JFrame<> 除非添加功能

这是您的代码并进行了上述修复(请原谅图片质量但必须调整大小或将变为 800x600):

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Polygon;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class JRisk {

    private JFrame mainMap;
    private Polygon poly;

    public JRisk() {

        initComponents();

    }

    private void initComponents() {

        mainMap = new JFrame();
        mainMap.setResizable(false);

        mainMap.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        int xPoly[] = {150, 250, 325, 375, 450, 275, 100};
        int yPoly[] = {150, 100, 125, 225, 250, 375, 300};

        poly = new Polygon(xPoly, yPoly, xPoly.length);
        JPanel p = new JPanel() {
            @Override
            protected void paintComponent(Graphics g) {
                super.paintComponent(g);
                g.setColor(Color.BLUE);
                g.drawPolygon(poly);
            }

            @Override
            public Dimension getPreferredSize() {
                return new Dimension(800, 600);
            }
        };
        mainMap.add(p);
        mainMap.pack();
        mainMap.setVisible(true);

    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new JRisk();
            }
        });
    }
}

根据您的评论:

i am preparing a map which includes lots of polygons and yesterday i used a JPanel over a JFrame and i tried to check if mouse was inside of the polygon with MouseListener. later i saw that mouseListener gave false responds (like mouse is not inside of the polygon but it acts like it was inside the polygon). so i deleted the JPanel and then it worked

这里是使用 MouseAdapter 和覆盖 mouseClicked 来检查点击是否在多边形内的更新代码。

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Polygon;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class JRisk {

    private JFrame mainMap;
    private Polygon poly;

    public JRisk() {
        initComponents();
    }

    private void initComponents() {

        mainMap = new JFrame();
        mainMap.setResizable(false);

        mainMap.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        int xPoly[] = {150, 250, 325, 375, 450, 275, 100};
        int yPoly[] = {150, 100, 125, 225, 250, 375, 300};

        poly = new Polygon(xPoly, yPoly, xPoly.length);

        JPanel p = new JPanel() {
            @Override
            protected void paintComponent(Graphics g) {
                super.paintComponent(g);
                g.setColor(Color.BLUE);
                g.drawPolygon(poly);
            }

            @Override
            public Dimension getPreferredSize() {
                return new Dimension(800, 600);
            }
        };

        MouseAdapter ma = new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent me) {
                super.mouseClicked(me);

                if (poly.contains(me.getPoint())) {
                    System.out.println("Clicked polygon");
                }

            }
        };
        p.addMouseListener(ma);//add listener to panel
        mainMap.add(p);

        mainMap.pack();
        mainMap.setVisible(true);

    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new JRisk();
            }
        });
    }
}

关于java - 关于在java中绘制多边形，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/15188238/