flickering help?

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

class Lazers extends JFrame {

    //define rectangles for the lazers and person
    int x = (int) (Math.random() * 780);
    final Rectangle guy = new Rectangle (375, 400, 50, 50 );
    final Rectangle lazer = new Rectangle ( x, 0, 7, 23 );
    Rectangle back = new Rectangle( 0, 0, 800, 500 );

    //holds the variables for the guy's movement
    int STOP = 0, LEFT = 1, RIGHT = 2;
    int guyDirection;

    //variables that check if player is intersecting the sides
    Rectangle leftSide = new Rectangle (780, 0, 5, 500);
    Rectangle rightSide = new Rectangle (0, 0, 5, 500);

    public static void main (String []args ) {
        Lazers frame = new Lazers();
        frame.setVisible(true);
    }

    public Lazers( ) { //DO NOT TOUCH!!!
        //set the frame default properties
        super ( "My Lazer Game");
        setSize ( 800,500 );
        setLocationRelativeTo ( null );
        setResizable (false);
        Image img = Toolkit.getDefaultToolkit().getImage( "guy.PNG" );
        setIconImage ( img );
        //register 'Exit upon closing' as a default close operation
        setDefaultCloseOperation( EXIT_ON_CLOSE );

        guyMove gm = new guyMove();
        gm.start();
    }

    public void paint(Graphics g) {
        //super.paint(g);
        g.setColor(Color.BLACK);
        g.fillRect(back.x, back.y, back.width, back.height);

        //put the guy's rectangle on the screen
        g.setColor(Color.BLUE);
        g.fill3DRect(guy.x,guy.y,guy.width,guy.height,true);
        //put the lazers on the screen
        g.setColor(Color.ORANGE);
        g.fill3DRect(lazer.x,lazer.y,lazer.width,lazer.height,true);
    }

    private class guyMove extends Thread implements KeyListener {
        public void run() {
            addKeyListener(this);
            while (true) {
                try {
                    repaint();
                    if (guy.intersects(leftSide) ||
                        guy.intersects(rightSide)) {
                            guyDirection = STOP;
                    }

                    if (guyDirection==STOP) {
                    }

                    if (guyDirection==LEFT) {
                        guy.x -= 5;
                    }

                    if (guyDirection==RIGHT) {
                        guy.x += 5;
                    }
                    Thread.sleep(75);
                }
                catch(Exception e) {
                    break;
                }
            }
        }

        public void keyPressed(KeyEvent event) {}
        public void keyReleased(KeyEvent event) {}
        public void keyTyped(KeyEvent event) {
            if (event.getKeyChar()=='a') {
                guyDirection = LEFT;
            }

            if (event.getKeyChar()=='d') {
                guyDirection = RIGHT;
            }
        }
    }
}