JLabel is in a wrong position in my JPanel

I have a class which extends JPanel and I want to add some labels (actually a class which extends JLabel) on it. The layout of this panel in null. i've set the size and the location of my label, but the problem is that i can't see it in the corr开发者_如何学编程ect place :( I printed getComponentAt(....).getClass().getName() in console to see what really exists in that location and got the correct answer (i mean getComponent says that there is a lable in the place where i added it, but the problem is that i see my label in position (0,0) which is wrong ) :-S i can't find any mistake in my code :-/ Any help is appreciated, thanks in advance. :) This the relevant part of my code:

public class ServerViewManager extends JPanel implements Serializable {

private ArrayList<String> map;
// *tankview extends JLabel
private ArrayList<TankView> tanks = new ArrayList<TankView>();
private ArrayList<BulletView> bullets = new ArrayList<BulletView>();
private int rows;
private int columns;

public ServerViewManager(ArrayList<String> map) {
    super(null);
    this.map = map;
    rows = map.size();
    columns = map.get(0).length();

    for (int i = 0; i < map.size(); i++) {
        for (int j = 0; j < map.get(i).length(); j++) {
            if (map.get(i).charAt(j) == 'i')
                add(new IceBlock(i, j));
            else if (map.get(i).charAt(j) != 'g')
                add(new Block(map.get(i).charAt(j), i * 50, j * 50));
        }
    }

}

public void paintComponent(Graphics g) {

    g.drawImage(Resources.GROUNDBLOCK.getImage(), 0, 0, columns * 50,
            rows * 50, this);
}
//************************************************
// Here is where i wanna put the label
public void addTank(Color color, int xpos, int ypos) {
    tanks.add(new TankView(color, xpos, ypos));
    if (iceBlock(xpos, ypos)) {
        IceBlock ice = (IceBlock) this.getComponentAt(ypos * 50, xpos * 50);
        ice.putItem(color + "1");
    } else
        this.add(tanks.get(tanks.size() - 1));
    repaint();
}

and here is my label:

public class TankView extends JLabel implements Serializable{

private int xpos;
private int ypos;
private char direction;
private int directionNum;
private Color color;

public TankView(Color color, int x, int y) {

    xpos=x;
    ypos=y;
    direction='u';
    directionNum=1;

    setLocation(ypos *50, xpos*50);
    setSize(50, 50);
    setOpaque(false);
    setVisible(true);


    this.color=color;
    if (color==Color.Blue)
        setIcon(Resources.BlueTank1);
    else if (color==Color.Green)
        setIcon(Resources.GreenTank1);
    else if (color==Color.Red)
        setIcon(Resources.OrangeTank1);
    else if (color==Color.Yellow)
        setIcon(Resources.PinkTank1);
    repaint();
}

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any of JComponents must be visible or you have to call pack(); to the top-level container, otherwise returns zero value for getBounds(); or getSize or getWhatever

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it may seems ridiculous, but i just made the methods below a comment and the problem was solved :O I don't really know why this happened. i hadn't even called them :-?? i was trying to post an SSCCE and i realized that everything was OK. Therefore I began making my own program exactly like the one i wanted to post (by making methods a comment)

// public int getX(){
// return xpos;
// }
//
// public int getY(){
// return ypos;
// }

these methods had to return the position of my tanks. (They were in TankView class)