Question

Originally (See my previous question “Java how to make JFrames start off as a maximised window“) I wanted to make a window which starts out maximised.
This code accomplishes this:

public static void main(String[] args)  {

JFrame frame = new JFrame();
frame.setExtendedState(JFrame.MAXIMIZED_BOTH);
frame.setVisible(true);

}

However, if this window is restored down it becomes a practically non-existent bar. To solve this I set a size for the window using setSize(). This works but presents another problem, the window can still be resized.

To solve this problem I set setResizable(false); and this is my code so far:

public static void main(String[] args) {

    Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();

    JFrame frame = new JFrame("Jedia");
    frame.setExtendedState(JFrame.MAXIMIZED_BOTH);
    frame.setSize(screenSize);
    frame.setResizable(false);
    frame.setVisible(true);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

However, now the window starts out at its specified size (rather than maximised) and cannot be restored up.

So, my question is, how can I either make the window start out maximised, give it a size for when it is restored down and make resizing it impossible? Or make a window that starts out maximised and cannot be restored down?

Answer 1

There is a simple fix that works almost all the time: make your frame not resizable after having set visible. So only modifies your code this way:

public static void main(String[] args) {

    Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();

    JFrame frame = new JFrame("Jedia");
    frame.setExtendedState(JFrame.MAXIMIZED_BOTH);
    frame.setSize(screenSize);
    frame.setVisible(true);    // FIRST visible = true
    frame.setResizable(false); // THEN  resizable = false
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

This way, the frame will start maximized and the maximize button will be greyed out, preventing user to use it. (I don’t really know why you have to do this. I suppose the maximized state is really applied only when the window becomes visible, and if you make it unresizable before, it will not apply.)

It works almost all the time because on Windows 7 at least you can make the window goes out of the maximized state by clicking the title bar and dragging it. But it will be at the size you have set it earlier. Problem is that your user will not be able to maximize it again, and I haven’t found the way with listeners to make the window back to maximized state. ( Edit: @David Kroukamp shows in the last part of his answer that it is possible to force the maximized state by using a ComponentListener. Therefore you don’t have to use setResizable(false) This way you still have a problem with Windows 7 because the dragging action is not catched by this event for whatever reason but users will be able to use the maximized button to put it back where it should be.)

Now, there is almost never a reason to do this kind of things. Users don’t really like when you prevent them to manipulate their windows (maximized windows can not be moved, for example, and that can be annoying when you have multiple screens). An exception is if you are making a game, which is typically full-screen. But then you wouldn’t want a JFrame because you don’t want all the decoration, but a Window.

If your problem is that the default window size is very small, it’s normal. You have to put something in your frame first (some controls, buttons, what you want in your application), using layouts (that’s important) then call the method pack() on your frame. It will chose a nice default size for your window.

Finally, a last word. I’ve put my example code in a main method as a shortcut, but you should always do Swing stuff in the Swing EDT by using SwingUtils.invokeLater().