Cfrgtkky

I'm working on a vertical scrolling game, and I'm using a thread to generate new enemies every 2 seconds. Each enemy is an image in a JPanel. For some reason, The generated enemies are not showing up in the JFrame, but they are present. When the player collides with one of the enemies, all the enemies show up.
Here's the code:

private void checkCollision() {

    for(AlienShip as : enemies) {

        if(player.getBounds().intersects(as.getBounds()))

            player.setVisible(false);

    }

}



private void setAlien() {

    alien = new AlienShip();

    add(alien);

    enemies.add(alien);

    System.out.println("Enemies: " + enemies.size());

}



public Thread alienGenerator() {

    for(int i = 0; i < 3; i++) { // these are being drawn

        setAlien();

    }



    return new Thread(new Runnable() {

        @Override

        public void run() {

            int sleepTime = 2000;

            while(true) {

                try {

                    Thread.sleep(sleepTime);

                } catch(InterruptedException e) {

                    System.out.println(e);

                }

                setAlien(); //these aren't

            }

        }

    });

}





private void gameLoop() {

    alienGenerator().start();

    mainTimer = new Timer(50, new ActionListener() {

        @Override

        public void actionPerformed(ActionEvent e) {

            repaint();

            checkCollision();

        }

    });

    mainTimer.start();

}

It always seems that you're Darned If You Do And Darned If You Don't. As far as I'm concerned the code you had placed in your earlier post was adequate, as a matter of fact, it was still lacking (no PlayerShip Class). The code example in this post does even less justice. Never the less......

Before I get started I just want you to know that I personally would have tackled this task somewhat differently and the meager assistance provided here will be solely based on the code you have already provided in this and previous posts.

The reason you are not seeing your Alien Ships displaying onto the Game Board upon creation is because you don't revalidate the board panel. As you currently have your code now this can be done from within the Board.setAlien() method where the Alien Ships are added. Directly under the code lines:

alien = new AlienShip();

add(alien);

enemies.add(alien);

add the code line: revalidate();, so the code would look like this:

alien = new AlienShip();

add(alien);

enemies.add(alien);

revalidate();

Your Alien Ships should now display.

On A Side Note:

What is to happen when any Alien Ship actually makes it to the bottom of the Game Board? As a suggestion, have them re-spawn to the top of the game board (serves ya right fer missin em). This can be done from within the AlienShip.scrollShip() method by checking to see if the Alien Ship has reached the bottom of the board, for example:

public void scrollShip() {

    if (getY() + 1 > this.getParent().getHeight()) { 

        setY(0 - PANEL_HEIGHT);

    }

    else {

        setY(getY() + 1);

    }

}

In my opinion, PANEL_HEIGHT is the wrong field name to use. I think it would be more appropriate to use something like ALIEN_SHIP_WIDTH and ALIEN_SHIP_HEIGHT. Same for the variables panelX and panelY, could be alienShipX and alienShipY. Food for thought.

As you can see in the code above the current Game Board height is acquired by polling the Game Board's getHeight() method with: this.getParent().getHeight(). This allows you to change the Game Board size at any time and the Alien Ships will know where that current boundary is when scrolling down. All this then means that the setResizable(false); property setting done in the Main Class for the Game's JFrame window can now be resizable: setResizable(true);.

You will also notice that when the Alien Ship is re-spawned at top of the Game Board it is actually out of site and it flows into view as it moves downward. I think this is a much smoother transition into the gaming area rather than just popping into view. This is accomplished with the setY(0 - PANEL_HEIGHT); code line above. As a matter of fact even when the game initially starts, your Alien Ships should flow into the the gaming area this way and that can be done from within the AlienShip.initAlienShip() method by initializing the panelY variable to panelY = -PANEL_HEIGHT;.

This now takes me to the initialization of the PANEL_WIDTH and PANEL_HEIGHT fields. The values seem enormous (224 and 250 respectively). Of course you may have set to these sizes for collision testing purposes, etc but I think an image size of 64 x 35 would most likely suffice:

This image should be a PNG image with a transparent background which then eliminates the need for the setBackground(Color.BLUE); code line located within the AlienShip.initAlienShip() method.

The AlienShip.getX() and AlienShip.getY() methods should be overridden:

@Override  

public int getX() { ... }



@Override  

public int getY() { ... }

I think extending the AlienShip Class to JLabel would be better than to JPanel. To JPanel seems like overkill:

public class AlienShip extends JLabel { ... }

Adding a background image to the Game Board can add pizazz to the game. This can be achieved by adding the following code to the Board.paintComponent() method:

@Override

public void paintComponent(Graphics g) {

    super.paintComponent(g);



    ImageIcon imgIcon = new ImageIcon("images/StarBackground.png");

    Image img = imgIcon.getImage();

    g.drawImage(img, 0, 0, this.getSize().width, this.getSize().height, this);

}

Images can be acquired here.

This should keep you going for a while. Before to long it'll be Alien mayhem.