线未显示在图像jframe上

Question

package carspeedometer;

import java.awt.Graphics;

import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

class a1 {

    a1() {
        JFrame jf = new JFrame("Speedometer");
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel jp = new JPanel();
        JLabel jb = new JLabel(new ImageIcon(
                "C:/Users/Vinayak/Desktop/tester.jpg"));
        jp.add(jb);

        jf.add(jp);
        jf.setVisible(true);
        jf.setSize(700, 700);
    }

    public void paint(Graphics g) {
        g.drawLine(70, 70, 200, 200);
    }

    public static void main(String...s) {
        new a1();
    }
}

Line is not showing on screen.I want to show line on top of the image.please help. Here i am trying to build a speedometer but first a line needs to be displayed

Answer 1

You can only draw in Swing if you override a drawing method of a component. Here your paint method overrides nothing because your class extends nothing. I suggest

• that you create a class that extends JPanel
• that you override the JPanel's paintComponent(Graphics g) method
• that you use the @Override annotation to verify the override
• that you place the JPanel into a JFrame and display it and
• that you read the Swing Painting Tutorials . You don't want to guess at this stuff.