java swing jframe size returns dimension bigger as screen

Question

While investigating some issue in my application, I just found out some weird thing.

Basically this SSCCE should demonstrate the problem:

public class MainFrame extends JFrame {
    public MainFrame() {
         setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
         setExtendedState(JFrame.MAXIMIZED_BOTH);
         pack();
    }
}

public class Main {
    public static void main(String[] args) {
        MainFrame mf = new MainFrame();
        mf.setVisible(true);
        System.out.println(mf.getSize());
    }
}

Somehow, on my 1280x1024 resolution monitor, this results in:

java.awt.Dimension[width=1296,height=1010]

Anyone knows how this is happening? Especially the fact that the width is higher than as what should happen.

Regards.

Answer 1

The window border is probably 8 pixels wide. When maximizing, Windows resizes the window so that the client area gets 1280 pixels wide. The whole width of the window is then 8+1280+8 pixels = 1296 pixels. The same happens to the height.

When using extended desktop on multiple monitors, one can sometimes notice that when a window is maximized on one screen, the window's border can be seen on adjacent screens.

Answer 2

Not sure what's happening there. If you're just trying to set your frame to it's maximum size based on available screen real estate, try this alternative:

import java.awt.*;
import javax.swing.*;

public class JFrameExtended
{
  public static void main(String[] args)
  {
    SwingUtilities.invokeLater(new Runnable()
    {
      public void run()
      {
        GraphicsEnvironment env = GraphicsEnvironment.getLocalGraphicsEnvironment();
        Rectangle maxBounds = env.getMaximumWindowBounds();

        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setBounds(maxBounds);
        f.setVisible(true);
        System.out.println("Frame size: " + f.getSize());
      }
    });
  }
}