How to double buffer awt objects

Question

I am trying to make a java program where you can draw (like paint) so far, I have pen size, and different colors. The only problem is the rectangles (theyre just there so you can see where to click) flicker whenever you're drawing. Here is my code:

import java.awt.*;
import java.awt.event.*;
import java.applet.*;

@SuppressWarnings({ "serial" })
public class DrawGame extends Applet implements MouseListener, MouseMotionListener, ActionListener {

    int x, y, width, height, colorx, colory, pen;
    boolean isRed = false, isYellow = false, isBlue = false, isGreen = false, isGrey = false, isBlack = false;
    String color = "Black";

    Image backbuffer;
    Graphics background;

    Button clear;
    CheckboxGroup radioGroup;
    Checkbox ps4, ps8, ps16, ps32, ps64;

    public void init() {
        clear = new Button("Clear");
        radioGroup = new CheckboxGroup();
        ps4 = new Checkbox("4", radioGroup, false);
        ps8 = new Checkbox("8", radioGroup, true);
        ps16 = new Checkbox("16", radioGroup, false);
        ps32 = new Checkbox("32", radioGroup, false);
        ps64 = new Checkbox("64", radioGroup, false);
        setLayout(new FlowLayout());
        setSize(900, 700);
        width = getSize().width;
        height = getSize().height;

        add(clear);
        add(ps4);
        add(ps8);
        add(ps16);
        add(ps32);
        add(ps64);

        setBackground(Color.WHITE);
        backbuffer = createImage(width, height);
        background = backbuffer.getGraphics();
        addMouseListener(this);
        addMouseMotionListener(this);
    }

    public void mousePressed(MouseEvent v) {
        if(x < 80) { //so you can't draw where the squares are
            colorx = v.getX();
            colory = v.getY();
        }
        if(colorx >= 25 && colory <= 50 && colory >= 25 && colorx <= 75) {
            isRed = true;
            isBlue = false;
            isBlack = false;
            isGreen = false;
            isGrey = false;
            isGreen = false;
            isYellow = false;
            color = "Red";
        }
        else if(colorx >= 25 && colory <= 100 && colory >= 75 && colorx <= 75) {
            isBlack = true;
            isRed = false;
            isBlue = false;
            isGreen = false;
            isGrey = false;
            isGreen = false;
            isYellow = false;
            color = "Black";
        }
        else if(colorx >= 25 && colory <= 150 && colory >= 125 && colorx <= 75) {
            isBlue = true;
            isBlack = false;
            isRed = false;
            isGreen = false;
            isGrey = false;
            isGreen = false;
            isYellow = false;
            color = "Blue";
        }
        else if(colorx >= 25 && colory <= 200 && colory >= 175 && colorx <= 75) {
            isGreen = true;
            isBlack = false;
            isRed = false;
            isBlue = false;
            isGrey = false;
            isYellow = false;
            color = "Green";
        }
        else if(colorx >= 25 && colory <= 250 && colory >= 225 && colorx <= 75) {
            isYellow = true;
            isBlack = false;
            isRed = false;
            isBlue = false;
            isGrey = false;
            isGreen = false;
            color = "Yellow";
        }
        else if(colorx >= 25 && colory <= 300 && colory >= 275 && colorx <= 75) {
            isGrey = true;
            isBlack = false;
            isRed = false;
            isBlue = false;
            isYellow = false;
            isGreen = false;
            color = "Yellow";
        }
        else{
            isBlack = false;
            isBlue = false;
            isRed = false;
            isGreen = false;
            isGrey = false;
            isGreen = false;
            isYellow = false;
            color = "Black";
        }
    }

    public void mouseDragged(MouseEvent v) {
        x = v.getX();
        y = v.getY();
        if(ps4.getState()) pen = 4;
        if(ps8.getState()) pen = 8;
        if(ps16.getState()) pen = 16;
        if(ps32.getState()) pen = 32;
        if(ps64.getState()) pen = 64;

        if(isRed == true) {
            background.setColor(Color.red);
        }
        else if(isBlue == true) {
            background.setColor(Color.blue);
        }
        else if(isGreen == true) {
            background.setColor(Color.GREEN);
        }
        else if(isYellow == true) {
            background.setColor(Color.YELLOW);
        }
        else if(isGrey == true) {
            background.setColor(Color.GRAY);
        }
        else{
            background.setColor(Color.black);
        }

        if(x > 80) {
            background.fillOval(x-(pen/2), y-(pen/2), pen, pen);
        }
        repaint();
        v.consume();
    }

    public void mouseMoved(MouseEvent v) {
        x = v.getX();
        y = v.getY();

        showStatus("Mouse co-ordinates: " + x + ", " + y + "                                                                Current selected color: " + color);
    }

    public void mouseClicked(MouseEvent v) {
        v.getX();
        v.getY();

        if(x > 80) {
            background.fillOval(x-(pen/2), y-(pen/2), pen, pen);
        }

        repaint();
        v.consume();
    }

    public void mouseEntered(MouseEvent v) {}

    public void mouseExited(MouseEvent v) {}

    public void mouseReleased(MouseEvent v) {}
    public void update (Graphics g) {
        g.drawImage(backbuffer, 0, 0, this);
        repaint();
    }
    public void squares(Graphics g) {
        g.setColor(Color.RED);
        g.fillRect(25, 25, 50, 25);
        g.setColor(Color.black);
        g.fillRect(25, 75, 50, 25);
        g.setColor(Color.BLUE);
        g.fillRect(25, 125, 50, 25);
        g.setColor(Color.GREEN);
        g.fillRect(25, 175, 50, 25);
        g.setColor(Color.YELLOW);
        g.fillRect(25, 225, 50, 25);
        g.setColor(Color.GRAY);
        g.fillRect(25, 275, 50, 25);
        repaint();
    }

    public void paint (Graphics draw) {
        update(draw);
        draw.drawImage(backbuffer, 0, 0, this);
    }

    public void actionPerformed(ActionEvent e) {}
}

Answer 1

First, it seems you are calling methods in an inappropriate way, producing a repeating cycle:

paint() invokes update()
update() invokes repaint()
repaint() invokes paint()
...

Then, respect to double buffering, I hope this link will be useful for you: Double Buffering with awt

Regards,