I am not sure what is incorrect

Question

I am creating a small Java Jpanel game in which I am supposed to have a rocket that moves up and down via arrows and fires via space.
The firing method should work like this: Space bar pressed, thing fires and moves across screen , and then when it hits a certain x, it disappears. Also, you can only fire once until the other bullet disappears.
I do not know what I am doing wrong. For one, as soon as my code starts you can see a bullet flying across the screen.
2nd, the bullet is not disappearing.
3rd, even though the other bullet is still visible, it allows me to fire again.

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.io.File;
import java.io.IOException;
import java.util.Random;   
import javax.imageio.ImageIO;
import javax.swing.*;
@SuppressWarnings("serial")

public class SpaceGame extends JPanel implements ActionListener{
    Timer t = new Timer(2, this);

    private ImageIcon rocket,asteroid,bullet;
    private JLabel rocketlabel,ast1,ast2,ast3,bulletLabel;
    public static int y=90,dy=0,bulletX=110,bulletY,i=0,canFire;
    //public sound sound;
    static boolean bulletFired=false;;
    static JFrame f = new JFrame();

    SpaceGame(){
        this.setBackground(Color.black);
        rocket = new ImageIcon(getClass().getResource("rocketFinal.png"));
        rocketlabel= new JLabel(rocket);
        this.add(rocketlabel);
        asteroid = new ImageIcon(getClass().getResource("asteroid.png"));
        ast1=new JLabel(asteroid);
        ast2=new JLabel(asteroid);
        ast3=new JLabel(asteroid);
        bullet = new ImageIcon(getClass().getResource("bulletReal.png"));
        bulletLabel = new JLabel(bullet);
        canFire=1;
        bulletLabel.setVisible(false);
         this.add(ast1);this.add(ast2);this.add(ast3);this.add(bulletLabel);

        f.addKeyListener(new controller());

        this.setLayout(null);
        this.setVisible(true);
    }

    public class controller implements KeyListener{

        @Override
        public void keyPressed(KeyEvent e) {
            int keyCode = e.getKeyCode();           

               if(keyCode== KeyEvent.VK_UP) {

                    dy=-1;

                   }
                if(keyCode== KeyEvent.VK_DOWN) {

                   dy=1;
                }
              if(keyCode== KeyEvent.VK_SPACE) {
                   if(canFire==0) {

                       System.out.println(String.valueOf(canFire));
                       bulletFired = true;

                       bulletY = y; 
                       bulletX=110;
                       }canFire=1;                      
              }
             }

        @Override
        public void keyReleased(KeyEvent e) {
            int key = e.getKeyCode();

            switch(key) {
            case KeyEvent.VK_UP: dy=0; break;
            case KeyEvent.VK_DOWN: dy=0; break;

            }
        }

        @Override
        public void keyTyped(KeyEvent e) {
            // TODO Auto-generated method stub              
        }

    }
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        rocketlabel.setBounds(45,y,rocket.getIconWidth(),80);
        fireBullet();

        paintStars(g);
        t.start();
    }

    public void paintStars(Graphics g) {
        g.setColor(Color.yellow);
        for(int i=0; i<5;i++) {

            Random rand = new Random();
            int o = rand.nextInt(500);
            int p = rand.nextInt(300);
            g.fillOval(o, p, 3, 3);

        }
    }
    public void actionPerformed(ActionEvent e) {
        if(y==-20) y=249;
        if(y==250)y=-20;
        y+=dy;
        if(bulletFired=true) {
            bulletX++;
            if(bulletX==455)bulletFired=false;bulletLabel.setVisible(false);System.out.println(String.valueOf(bulletX)); canFire=0; 

        }

        repaint();
    }
    public void fireBullet(){
    if(bulletFired=true) {
        bulletLabel.setVisible(true);
        bulletLabel.setBounds(bulletX,bulletY+25,bullet.getIconHeight(),bullet.getIconWidth());
    }

   }

    public static void main(String[] args) {
        String filepath = "SpaceGameMusic.wav";
        musicStuff musicPlayer = new musicStuff();

        musicPlayer.playMusic(filepath);
        SpaceGame t = new SpaceGame();

        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(t);
        f.setSize(500,335);
        f.setVisible(true);
        f.setResizable(false);
    }
}

Answer 1

The problem was quite simply that I had forgotten to use == in my if(boolean) statements.

Answer 2

For one, as soon as my code starts you can see a bullet flying across the screen.

The paintComponent() method is for painting only. You can't control when Swing will determine a component needs to be repainted.

So, for example:

t.start();

should NOT be in the painting method. As soon as the frame is made visible the panel will be painted and the Timer will be started.

You application code should control when the Timer is started.

Other issues:

1. you should not be using static variables. The variable should simply be instances of your class.

2. the paintStars() method should not generate random locations. Again. a painting method should only paint the current state of the class. So if you want to change the location of the stars you should have a method like randomizeStars(). In this method you would update an ArrayList of Point objects. Each Point instance would represent the location of a star. Then the paintStars() method would simply iterate through the ArrayList and paint each star.

3. you should not be using a KeyListener. A KeyListener only works if a component has focus. You can't guarantee that your component will lose focus. Instead you should be using Key Bindings. Key bindings allow you to handle a KeyEvent even if the component doesn't have focus. See Motion Using the Keyboard for more information and a working example.

you can only fire once until the other bullet disappears

Your canFire variable should be a boolean variable so it only has true/false values. Again you have a method that sets the state. Your game logic will then check the state before firing the bullet again.

if(y==-20) y=249;
if(y==250)y=-20;

Don't hardcode values. The number should be based on the size of your panel. So you use methods like getWidth() and getHeight() to determine the current size of the panel.