import java.awt.*; import java.awt.geom.*; /** * A circle that can be manipulated and that draws itself on a canvas. * * @author Michael Kolling and David J. Barnes * @version 2006.03.30 */ public class Circle { private int diameter; private int xPosition; private int yPosition; private String color; private boolean isVisible; /** * Create a new circle at default position with default color. */ public Circle() { diameter = 30; xPosition = 20; yPosition = 60; color = "blue"; isVisible = false; } /** * Make this circle visible. If it was already visible, do nothing. */ public void makeVisible() { isVisible = true; draw(); } /** * Make this circle invisible. If it was already invisible, do nothing. */ public void makeInvisible() { erase(); isVisible = false; } /** * Move the circle a few pixels to the right. */ public void moveRight() { moveHorizontal(20); } /** * Move the circle a few pixels to the left. */ public void moveLeft() { moveHorizontal(-20); } /** * Move the circle a few pixels up. */ public void moveUp() { moveVertical(-20); } /** * Move the circle a few pixels down. */ public void moveDown() { moveVertical(20); } /** * Move the circle horizontally by 'distance' pixels. */ public void moveHorizontal(int distance) { erase(); xPosition += distance; draw(); } /** * Move the circle vertically by 'distance' pixels. */ public void moveVertical(int distance) { erase(); yPosition += distance; draw(); } /** * Slowly move the circle horizontally by 'distance' pixels. */ public void slowMoveHorizontal(int distance) { int delta; if(distance < 0) { delta = -1; distance = -distance; } else { delta = 1; } for(int i = 0; i < distance; i++) { xPosition += delta; draw(); } } /** * Slowly move the circle vertically by 'distance' pixels. */ public void slowMoveVertical(int distance) { int delta; if(distance < 0) { delta = -1; distance = -distance; } else { delta = 1; } for(int i = 0; i < distance; i++) { yPosition += delta; draw(); } } /** * Change the size to the new size (in pixels). Size must be >= 0. */ public void changeSize(int newDiameter) { erase(); diameter = newDiameter; draw(); } /** * Change the color. Valid colors are "red", "yellow", "blue", "green", * "magenta" and "black". */ public void changeColor(String newColor) { color = newColor; draw(); } /** * Draw the circle with current specifications on screen. */ private void draw() { if(isVisible) { Canvas canvas = Canvas.getCanvas(); canvas.draw(this, color, new Ellipse2D.Double(xPosition, yPosition, diameter, diameter)); canvas.wait(10); } } /** * Erase the circle on screen. */ private void erase() { if(isVisible) { Canvas canvas = Canvas.getCanvas(); canvas.erase(this); } } }