如何在图像图标上绘制黑色矩形？

Question

in my application I have a cross road picture in the background and I want to draw traffic lights on the top of it (black rectangle with 3 circles) The problem is, I cannot see the rectangle at all, as if it was under the image or something. And if I switch the order in which the items are painted, I get all black image.

Do you have any idea how this can be solved?I am new to graphics and searched similar questions, but none helped me. Thank you.

public MainFrame() throws HeadlessException {
    super("semafor");        
    crossroad = new ImageIcon("cross.png");

    initFrame();
    initComponents();

    sem1 = new Semafor(true, 100, 100);
    add(sem1);

    repaint();
    setVisible(true);
}

//here I paint the image
@Override
public void paint(Graphics g) {
    super.paint(g);
    g.drawImage(crossroad.getImage(), 0, 45, this);

}

//and in class Semafor i paint the actual traffic lights

@Override
public void paint(Graphics g) {
    g.setColor(Color.black);
    g.fillRect(0, 0, getWidth(), getHeight());
    g.setColor(Color.darkGray);

    //and then the circles
}

Answer 1

The first thing I'm noticing is that you are calling <unknown>.getWidth() and <unknown>.getHeight() for the rectangle size. If it's covering the entire image, this suggests that it is getting that width and height from the panel it is being drawn on.

A simple stack trace,

(new Exception).printStackTrace();

or

Thread.dumpStack();

will tell you as much. You could also query the width and height with a System.out call to verify that you're getting the values you're expecting, or, if this really gets out of control, learn to use JUnit and the assert statement. Honestly, though, it looks like you're just accidentally calling the wrong method.