JFrame : Java Glossary

Tips

• You don’t use jFrame.add( child ); you use jFrame.getContentPane().add( child ). This is especially infuriating since the compiler cannot catch the error. Similarly instead of jFrame.setLayout( layoutManager ) you use jFrame.getContentPane().setLayout( layoutManager ). Ditto for jFrame.getContentPane().setBackground( Color ) and jFrame.remove( child ). Java version 1.5 or later is more forgiving and your code still works if you forget to use contentPane.
• You continue to use jFrame.setSize, jFrame.validate and jFrame.setVisible.
• You can get a decorated frame with JFrame.setDefaultLookAndFeelDecorated( true ); The unusual thing is this is a static method on JFrame, not a method for JFrame objects.
• You can change the coffee cup icon for the Jframe with setIconImage.
• The AWT (Advanced Windowing Toolkit) equivalent of Jframe is called Frame.
• You nearly always set your own layout manager since by default Jframe comes with the lame BorderLayout.
• Jframe is a heavyweight component, more like an AWT component than a Swing one. It does not have a paintComponent, but an AWT-style paint. Don’t paint directly on it. Paint on a JPanel instead and insert that in the Jframe.

Co-ordinate System

When you specify the Jframe size, make it 22 pixels wider and 32 pixels taller than you need for the contents to allow room for the top Jframe bar. To add to the confusion, the origin is in the top corner under the Jframe bar. So you must add 32 to all your y coordinates inside a Jframe. This is one more reason to use layouts and avoid absolute positioning.

There are four way Jframe sizes could have been measured: all combinations of including or excluding the title bar and including or excluding the border. Oracle chose to include both. The easiest way to calculate a Jframe size is to manually adjust the Jframe until it looks right, then take a snapshot of it with PaintShop Pro, including the title bar and borders and use PSP’s size as your jFrame.setSize to set the initial size.

Jframe State

// turn off the entire frame bar, including title, close, minimize, resize...
frame.setUndecorated( true );

// turn off just resizing controls
frame.setResizable( false );

// You can control the current state of the Frame,
// but you cannot disable the corresponding user controls.
// To control the widgets, use a JInternalFrame.

frame.setExtendedState( NORMAL );
frame.setExtendedState( ICONIFIED );
frame.setExtendedState( MAXIMIZED_HORIZ );
frame.setExtendedState( MAXIMIZED_VERT );
frame.setExtendedState( MAXIMIZED_BOTH );

Beware. getExtendedState in a componentResized event handler gives you the old state. You could use SwingUtilities. invokeLater or EventQueue. invokeLater to probe the new state.

IsA vs HasA

There are two techniques for creating a frame full of components.

1. Extend Jframe with private variables, getters and setters.
2. Create a class with private variables, getters and setters that contains a reference to a standard Jframe object.

Advantages of Extension

• Terser
• Simpler
• Most tutorials teach it this way.

Advantages of Composition

• Better separation of logic
• Avoids exposing all the methods of Jframe (which is both an advantage and disadvantage).
• It gives greater freedom to reimplement with something other than Jframe without having to change all the referencing code.
• Logically speaking, your application has a Jframe. It is not a species of Jframe.
• Most professional programmers prefer to do it this way.

Debugging Harness

Here is a typical debugging harness you would append to every Jframe you write. Note how all initialisation is done on the Swing event thread via SwingUtilities.

Caller/Callee Responsibility

Normally the caller who instantiates the Jframe does a setSize to determine its size, then a setLocation to position it, then a validate and finally a setVisible ( true ).

You might do a setSize and setLocation in the constructor, but definitely not a setVisible. setTitle may be done by either.

Jframe Closing

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