My JFrame size doesn't match up with set size

Question

I am using frame.setSize(480, 400) to set the size of my JFrame. Despite this, when I am doing some collision checking (I am making a breakout game), the ball goes completely off the bottom of the screen, then finally bounces. This is the collision code I'm using: if (YPos + height >= MainClass.height) { YVel = YVel * -1; } if (YPos + height >= MainClass.height) { YVel = YVel * -1; } . The static height variable is what is set to 400, and used in the frame.setSize call. This has happened in my pong game aswell, although I fixed it with some hard set values. I wouldn't like to repeat this though, as this is bad practice.

Thanks for any responses, Rees.

Answer 1

1. don't to set frame.setSize(480, 400) or frame.setPreferredSize(480, 400)

2. for painting to use JPanel / JComponent , then return coordinates from this container

3. painting in Swing by default never returns any PreferredSize have to override PreferredSize for JPanel / JComponent , (see dim.width , dim.height this methods returns proper coordinates for Object (s) added to JPanel / JComponent , after resize too)

4. then call (last code lines) JFrame.pack() and JFrame.setVisible(true)

5. JFrame doesn't returns proper coordinated have to calculating with its Borders and Toolbar , but ContentPane return inner and proper size

Answer 2

Frames have borders. These borders sit INSIDE the available space provided, meaning the available space for contents is the frame size - border insets

Instead, set the preferred size of the content and use JFrame#pack to compute the frame size

Check out

• How can I set in the midst?
• Graphics rendering in title bar

For some examples and more details