Basic HTML version of Foils prepared 18 May 97

Foil 5 Changing Graphics: repaint 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


Most applets and windows applications want to change what is drawn on the screen over its lifetime. This can be a sequenced animation, response to user input or mouse events, and so on.
Whenever you want to redraw the screen, call
  • void repaint();
Repaint gets the graphics context and creates a thread to call update, which calls your paint function. So all your drawing changes can also be put into paint.
One draws a sequence of text and shapes to define the screen, where the position of the object in the screen is given by pixel coordinates. If one object overlaps another, the latest one drawn covers up the area of overlap.
  • The exception to this is XOR graphics, which may be used to temporarily highlight a particular color. This is an advanced technique as other colors will also be affected.



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