屏幕上未显示我的图形

Question

I am trying to print out a horizontal line of small circles at regular distance intervals across the middle of my window. It is required of me to do this using recursion. I use the constructors when I call my recursive method to increment the position of the circle on the screen to create the line but no graphics are being printed out on my screen?

package weekFour;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.MouseInfo;
import java.awt.Point;
import java.awt.RenderingHints;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.Random;

import javax.swing.*;

@SuppressWarnings("serial")
public class Circle extends JPanel {
    private static final int PREF_W = 200;
    private static final int PREF_H = PREF_W;
    private Color circleColor = Color.RED;   //starting colour
    private Color circleColor2 = Color.BLUE;
    private Color squareColor = Color.GREEN;
    private Color squareColor2 = Color.YELLOW;
    private int circX  = -15;
    private int circY = circX;
    private int circW = PREF_W - 2 * circX;
    private int circH = PREF_H - 2 * circY;
    private static int windowW = 2000;
    private static int windowH = 1000;

    public Circle() {
    }

    protected void paintComponent(Graphics g, int xval, int yval, int diameter) {
        super.paintComponent(g);

        Graphics2D g2 = (Graphics2D) g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); //smoothes out edges

        g2.setColor(circleColor);
        g2.fillOval(xval, yval, diameter, diameter);
        g2.setColor(Color.BLACK);
        g2.drawOval(xval, yval, diameter, diameter);

        paintComponent(g, circX + 25, 450, 12);

    }   

    private static void createAndShowGui() { //code for GUI visuals
        JFrame frame = new JFrame("MyTaskToo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(new Circle());
        frame.setSize(windowW, windowH);
        frame.setVisible(true);
    }

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

Thanks for your time

Answer 1

Start by taking a look at Painting in AWT and Swing and Performing Custom Painting for more details about how painting works.

You should be overriding the paintComponent(Graphics g) methods (notice, no extra parameters), but before you do this, you will want to change your approach as your recursive method calls won't work.

Instead, you'll need some kind of background thread that can trigger a new paint update at a regular interval

Take a look at Concurrency in Swing for the dangers inolved in doing this and How to use Swing Timers for a possible solution

Answer 2

//you need to add a line in the end to repaint.
Circle()

{

repaint();

}