Why is my JPanel smaller than it should be?

Question

I am trying to learn Swing and have made a panel (with help from other StackOverflow code). I added a checkerboard design on a frame, but I have found that the frame is not as big as it should be.

Here is my code:

 @Override protected void paintComponent(Graphics g) { int width = getWidth(), height = getHeight(); g.clearRect(0, 0, width, height); g.setColor(Color.BLACK); for (int i=0;i<=width;i+=50) { g.drawLine(0,i,width,i); } for (int i=0;i<=height;i+=50) { g.drawLine(i,0,i,height); } label.setText("H = "+ getHeight() +" W = "+ getWidth()); // check actual size add(label); } private void gui(Pan window) { frame = new JFrame(); Container container = frame.getContentPane(); container.add(window); frame.setSize(400, 400); // size written here frame.setVisible(true); }

If you run it, you'll see the size of the window. It will be 362 by 384, instead of 400 by 400 as written in the code.

If I change the dimensions to 500 by 500, the window will be 462 by 484.

Q: Why are the dimensions off by 38 and 16?

Java adds insets for the borders. See stackoverflow.com/questions/2451252/… — blueygh2
– blueygh2, Commented Mar 29, 2014 at 16:45

Gilbert Le Blanc · Accepted Answer · 2014-03-29 18:37:30Z

6

It will be 362 by 384, instead of 400 by 400

Because the size of the frame include the title bar and borders. Don't use the setSize() method.

Instead override the getPreferredSize() method of your custom panel to return the size that you want the panel to be.

Then you use:

frame.pack();

Then the size of the frame will be the preferred size of your panel, plus the size of the title bar and borders.

edited Mar 29, 2014 at 18:37

Gilbert Le Blanc

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answered Mar 29, 2014 at 16:45

camickr

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2 Comments

Chronicle Over a year ago

Overriding getPrefferedSize() worked great! Returning a dimension of 400 by 400 makes the window the correct size. However, if I add setResizable(false), it becomes 410 by 410. Thoughts?

camickr Over a year ago

@Chronicle, setResizable() should be done before you pack the frame. The frame is still assuming a Border of 5 pixels for the resizable Border. Since there is not border, the extra space goes to the panel.

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