Keeping the rectangle within JFrame

Question

I know I am being an idiot and that's why I can't figure it out but I am trying to paint a bunch of rectangles with randoms size and position using paintComponent. I am trying to make sure that all of them are painted within the frame. I am able to do it with the following code (snippet) but I am wondering if there is a better way to do it than me hardcoding numbers into the program. Is there a method that I should take a look at that might be what I'm looking for?

Here's the inner class that overrides the paintComponent() method:

class DrawPanel extends JPanel {
    public void paintComponent(Graphics g) {
        int red = (int)(Math.random()*256);
        int blue = (int)(Math.random()*256);
        int green = (int)(Math.random()*256);

        g.setColor(new Color(red, blue, green));
        //The following 4 lines keep the rects within the frame
        //The frame is 500,500
        int ht = (int)(Math.random()*400);
        int wd = (int)(Math.random()*400);

        int x = (int)(Math.random()*100);
        int y = (int)(Math.random()*100);

        g.fillRect(x,y,ht,wd);
    }
}

What problems are you having? Are you sure that you want to randomize within `paintComponent(...)`, such that any time the gui is repainted for any reason, the rectangles will change. And are you sure that you don't want to call the `super.paintComponent(...)` method? — Hovercraft Full Of Eels, Dec 08 '12 at 16:48
Also, shouldn't you be using the `getSize()` of the DrawPanel and not use the JFrame's size? Else you are ignoring its title bar etc... — Hovercraft Full Of Eels, Dec 08 '12 at 16:50
See related examples [here](http://stackoverflow.com/q/9849950/230513). — trashgod, Dec 08 '12 at 16:53
Thanks Reimeus, Hovercraft and Lucas. The program was working as it was supposed to even before. The coding was just ugly and as you guys pointed out, a little wrong too. — Nico, Dec 08 '12 at 17:31

score 4 · Answer 1 · answered Dec 08 '12 at 16:51

4

I am wondering if there is a better way to do it than me hardcoding numbers into the program.

Yes there is

call getSize() on the enclosing JPanel, the DrawPanel, so you can see the actual boundaries of the component that is being drawn upon. (edit: or getWidth() and getHeight() as recommended by Lucas -- 1+ to his answer!).
Also, you will usually want to call the super's paintComponent(...) method within the child's override.
Also you will usually want to do your randomization elsewhere, such as in the DrawPanel's constructor so as not to change your rectangles each time you re-size the GUI.

answered Dec 08 '12 at 16:51

Hovercraft Full Of Eels

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For his purposes, wouldn't calling getHeight() and getWidth() be better since getSize() returns a Dimension? – Lucas Dec 08 '12 at 16:53
@Lucas: either could work well. 1+ to your answer by the way. – Hovercraft Full Of Eels Dec 08 '12 at 16:53
True, it's slightly simpler to do it with the separate methods, but faster to do it with getSize() if you know what you're dong. – Lucas Dec 08 '12 at 16:54

Reimeus · Accepted Answer · 2012-12-08T17:20:19.247

4

You should base your co-ordinates & sizes on the DrawPanel component size. Also using Random.nextInt instead of Math.random() will make it easier to keep within range based on the current size of the panel:

Random random = new Random();
int ht = random.nextInt(getHeight());
int wd = random.nextInt(getWidth());

int x = random.nextInt(getWidth() - wd);
int y = random.nextInt(getHeight() - ht);

edited Dec 08 '12 at 17:20

answered Dec 08 '12 at 16:53

Reimeus

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This is what I was looking for. Thanks a lot. I've upvoted all the other answers too since they were all helpful but this fixed the "problem". – Nico Dec 08 '12 at 17:29

score 2 · Answer 3 · answered Dec 08 '12 at 16:51

There is a method to get the length and width of the panel you are working in.

getHeight();
getWidth();

These will return the current size of the JPanel you are working in, meaning if you resize the window it'll actually still draw them inside.

http://docs.oracle.com/javase/7/docs/api/javax/swing/JComponent.html#getWidth()

Keeping the rectangle within JFrame

3 Answers3