在 JFrame 上画一条线

I am trying to draw a line using the Graphics 2D but then the line appears over all the other components in the JFrame thus making them invisible. How do I correct this problem?

代码如下:

import javax.swing.*;
import java.awt.*;
import java.awt.geom.*;

class Success extends JFrame{

    public Success(){
        JPanel panel=new JPanel();
        getContentPane().add(panel);
        setSize(450,450);

        JButton button =new JButton("press");
        panel.add(button);
    }

    public void paint(Graphics g) {
        Graphics2D g2 = (Graphics2D) g;
        Line2D lin = new Line2D.Float(100, 100, 250, 260);
        g2.draw(lin);
    }

    public static void main(String []args){
        Success s=new Success();
        s.setVisible(true);
    }
}

推荐答案

import javax.swing.*;
import java.awt.*;
import java.awt.geom.*;

class Success extends JFrame{

    public Success(){
        JPanel panel=new JPanel();
        getContentPane().add(panel);
        setSize(450,450);

        JButton button =new JButton("press");
        panel.add(button);
    }

    public void paint(Graphics g) {
        super.paint(g);  // fixes the immediate problem.
        Graphics2D g2 = (Graphics2D) g;
        Line2D lin = new Line2D.Float(100, 100, 250, 260);
        g2.draw(lin);
    }

    public static void main(String []args){
        Success s=new Success();
        s.setVisible(true);
    }
}

更多提示

1. 在 EDT 上创建 GUI.有关详细信息，请参阅 Swing 中的并发.
2. 按照@nIcEcOw 的建议使用JPanel，覆盖paintComponent(Graphics) 而不是paint().再次，首先调用 super 方法.
3. 不要扩展框架，只使用一个实例.使用pack()根据组件所需空间设置大小.