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Chapter: Java The Complete Reference - The Java Library - Using AWT Controls, Layout Managers, and Menus

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A Word About Overriding paint( ) - AWT

Before concluding our examination of AWT controls, a short word about overriding paint( ) is in order. Although not relevant to the simple AWT examples shown in this book, when overriding paint( ), there are times when it is necessary to call the superclass implementation of paint( ).

A Word About Overriding paint( )

 

Before concluding our examination of AWT controls, a short word about overriding paint( ) is in order. Although not relevant to the simple AWT examples shown in this book, when overriding paint( ), there are times when it is necessary to call the superclass implementation of paint( ). Therefore, for some programs, you will need to use this paint( ) skeleton:

 

public void paint(Graphics g) {

 

     //code to repaint this window

 

     //Call superclass paint()

 

     super.paint(g);

 

}

In Java, there are two general types of components: heavyweight and lightweight. A heavyweight component has its own native window, which is called its peer. A lightweight component is implemented completely in Java code and uses the window provided by an ancestor. The AWT controls described and used in this chapter are all heavyweight.

However, if a container holds any lightweight components (that is, has lightweight child components), your override of paint( ) for that container must call super.paint( ). By calling super.paint( ), you ensure that any lightweight child components, such as lightweight controls, get properly painted. If you are unsure of a child component’s type, you can call isLightweight( ), defined by Component, to find out. It returns true if the component is lightweight, and false otherwise.

 

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