The Way of the Java/The Slate Class

The Slate Class verbatim import java.awt.*; public class Example // demonstrate simple use of the Slate class public static void main (String[] args) int width = 500; int height = 500; Slate slate = Slate.makeSlate (width, height); Graphics g = Slate.getGraphics (slate); g.setColor (Color.blue); draw (g, 0, 0, width, height); anim (slate, 0, 0, width, height); // draw is taken from Section 4.14 of the book public static void draw (Graphics g, int x, int y, int width, int height) if (height < 3) return; g.drawOval (x, y, width, height); draw (g, x, y+height/2, width/2, height/2); draw (g, x+width/2, y+height/2, width/2, height/2); // anim demonstrates a simple animation public static void anim (Slate slate, int x, int y, int width, int height) Graphics g = slate.image.getGraphics (); g.setColor (Color.red); for (int i=-100; i<500; i+=8) g.drawOval (i, 100, 100, 100); slate.repaint (); try Thread.sleep(10); catch (InterruptedException e) class Slate extends Frame // image is a buffer: when Slate users draw things, they // draw on the buffer. When the Slate gets painted, we // copy the image onto the screen. Image image; public static Slate makeSlate (int width, int height) Slate s = new Slate (); s.setSize (width, height); s.setBackground (Color.white); s.setVisible (true); s.image = s.createImage (width, height); return s; // when a Slate user asks for a Graphics object, we give // them one from the off-screen buffer. public static Graphics getGraphics (Slate s) return s.image.getGraphics (); // normally update erases the screen and invokes paint, but // since we are overwriting the whole screen anyway, it is // slightly faster to override update and avoid clearing the // screen public void update (Graphics g) paint (g); // paint copies the off-screen buffer onto the screen public void paint (Graphics g) g.drawImage (image, 0, 0, null); verbatim