在JFrame上画一条线

问题描述

我正在尝试使用Graphics 2D绘制一条线，但是该线出现在所有JFrame中的其他组件，因此使其不可见.我该如何解决这个问题?

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

这是代码:

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.有关更多详细信息，请参见 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. 不扩展框架，仅使用一个实例.使用pack()根据组件所需的空间设置大小.

1. Create the GUI on the EDT. See Concurrency in Swing for more details.
2. Use a JPanel as suggested by @nIcEcOw, override paintComponent(Graphics) instead of paint(). Again, call the super method first.
3. Don't extend frame, just use an instance of one. Set the size according to the space required for the components using pack().

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