How to remove rectangles from my JFrame

[nickecarlo]

I have this program where when I click start, it starts painting rectangles one on top of the other by storing each rectangle created by paintComponent in an array and then displaying them on the screen.

When I click stop, the animation stops.

This is all fine and dandy but I have been banging my head against the computer to create a way where when I hit start after hitting stop, it would clear the screen and start the animation anew. I am pasting my code below, any help will be greatly appreciated.

import javax.swing.*;
import java.awt.event.*;
import java.util.ArrayList;
import java.util.Random;
import java.awt.*;

public class TwoButtonsRandomRec {

    JFrame frame;
    Timer timer;

    public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
        @Override
        public void run() {
            TwoButtonsRandomRec test = new TwoButtonsRandomRec();
            test.go();
        }
        });
    }

    public void go() {
    frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    JButton startButton = new JButton("Start");
    startButton.addActionListener(new StartListener());
    JButton stopButton = new JButton("Stop");
    stopButton.addActionListener(new StopListener());

    final DrawPanel myDraw = new DrawPanel();

    timer = new Timer(50, new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent ae) {
            myDraw.repaint();
        }
        });

    frame.add(startButton, BorderLayout.NORTH);
    frame.add(stopButton, BorderLayout.SOUTH);
    frame.add(myDraw, BorderLayout.CENTER);
    frame.pack();
    frame.setVisible(true);
    }

    class StartListener implements ActionListener {
    public void actionPerformed(ActionEvent e) {
        timer.start();
    }
    }

    class StopListener implements ActionListener {
    public void actionPerformed(ActionEvent e) {
        timer.stop();
    }
    }

    class DrawPanel extends JPanel {
    ArrayList<MyRectangle> rects = new ArrayList<>();
    Random rand = new Random();

    @Override
    public void paintComponent(Graphics g) {

        super.paintComponent(g);

        addRect();

        for(MyRectangle r : rects) {
        g.setColor(r.getColor());
        g.fillRect(r.x, r.y, r.width, r.height);
        }
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(500,500);
    }

    public void addRect() {
        int ht = rand.nextInt(getHeight());
        int wd = rand.nextInt(getWidth());

        int x = rand.nextInt(getWidth() - wd);
        int y = rand.nextInt(getHeight() - ht);

        int r = rand.nextInt(256);
        int g = rand.nextInt(256);
        int b = rand.nextInt(256);

        rects.add(new MyRectangle(x, y, wd, ht, new Color(r, b, g)));
    }
    }
}

class MyRectangle extends Rectangle {
    Color color;
    public MyRectangle(int x, int y, int w, int h, Color c) {
    super(x, y, w, h);
    this.color = c;
    }

    public Color getColor() {
    return color;
    }
}

[JamesCherrill]

Can't you just clear the contents of rects?

[nickecarlo]

I have tried to do that with:

rects.clear();

Sure that would work if only I knew how to bind that with my Start button only the second time that I press it.

I am pretty new at this stuff so I'm sure I'm missing something really simple but for now I can't seem to figure it out at all.

[JamesCherrill]

What harm wouild it do if youcleared rects every time you pressed start? The first tim erects would be empty, so clear would do nothing, in a harmless kind of way.