Java Notes: Window Size and Position

First pack your window to do the layout

The optimum size of a window depends on the size and layout of the components. After adding all the components to a window (JFrame), call pack() to perform the layout.

Centering a Window

The following code positions a window (JFrame) f in the center of the screen. Use this when you create a window, after calling pack() has been called, as follows.

setLocationRelativeTo(null);    // Implicit "this" if inside JFrame constructor.

f.setLocationRelativeTo(null);  // Explicit JFrame if outside JFrame constructor.

NetBeans. In the GUI Editor (Matisse) generated source code, add the following statement to the constructor that is automatically generated.

public SortDemoGUI() {  // Matisse generated constructor for SortDemoGUI class.
    initComponents();   // Matisse generated call to initialization method.
    setLocationRelativeTo(null);  // Add this line to center JFrame.
}

You can use the older, more explicit, way of centering a window

Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
Dimension windowSize = window.getSize();

int windowX = Math.max(0, (screenSize.width  - windowSize.width ) / 2);
int windowY = Math.max(0, (screenSize.height - windowSize.height) / 2);

f.setLocation(windowX, windowY);  // Don't use "f." inside constructor.

The Math.max call makes sure the window origin is not negative.

Expanding a window to fit the screen

The first example leaves a 4 pixel border around the window. The second example passes the Dimension object directly to setSize(). You don't need the explicit "f." if this code is in the constructor.

Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
f.setSize(screenSize.width - 4, screenSize.height - 4);
f.validate();                // Make sure layout is ok

Completely full screen.

f.setSize(Toolkit.getDefaultToolkit().getScreenSize());
f.validate();                // Make sure layout is ok

Fixed Window Size using setSize() and validate() - Probably a mistake

You can set the size of a window, but it's almost always a mistake unless you're simply expanding the window to fill the screen. The default window size should depend on the size and layout of the components as determined by pack(). If you must create a fixed size window (JFrame), call setSize(width, height) or setSize(dimension), then call validate() to finalize the component layout before making the window visible.