Basic HTML version of Foils prepared 18 May 97

Foil 4 Graphics is Event-Driven: paint method

From Java Tutorial - Spring 1997 Part 3:Graphics and the Abstract Windowing Toolkit Peking Tutorial, Web Certificate -- Spring-Summer 1997. by Nancy J. McCracken,Geoffrey C. Fox


In every applet or windows application, the windowing system creates an Image with a Graphics object to keep track of the state of the window.
In order to draw or write text to the window, you must override the paint method:
  • void paint(Graphics g)
In this method you put everything you want to draw in the window. The Graphics object g has things like a current color and current font, and there are methods for you to change these as well as draw.
The window system can be interrupted for various reasons - the user resized it or some other window was put on top of it and then removed - and it does not save a copy of the pixels. Instead it calls a method called update, which blanks the screen and then calls paint(g). So even if you only draw one window, paint can be called many times.



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