Drawing a line on a JFrame

问题

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?

Here's the code :

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);
    }
}

回答1:

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);
    }
}

Further tips

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

来源：https://stackoverflow.com/questions/10767265/drawing-a-line-on-a-jframe

标签

java

swing

jframe

graphics2d