die.java

Java程序设计(美) David D. Riley著 机械工业出版社 书籍配套 代码

/** class invariant:
 *      This class maintains a single die.
 *      and  dieRect.getWidth() == dieRect.getHeight() == 70
 *      and  1 <= spotCount <= 6
 *      and  spotCountSameAsDotsAdded()
 */
import java.awt.Color;
public class Die {
		private int numberOfSpots;
		private Rectangle dieRect;
		private Oval topLeftSpot, midLeftSpot, botLeftSpot, middleSpot, 
                topRightSpot, midRightSpot, botRightSpot;
    
		/** post:	spotCount() == 1
		 *         	and  dieRect.getBackground() == Color.black
		 */
		public Die() {
			dieRect = new Rectangle(0, 0, 70, 70);
			topLeftSpot = newSpot(10, 10);
			midLeftSpot = newSpot(10, 30);
			botLeftSpot = newSpot(10, 50);
			middleSpot = newSpot(30, 30);
			topRightSpot = newSpot(50, 10);
			midRightSpot = newSpot(50, 30);
			botRightSpot = newSpot(50, 50);
			setSpotCount(1);
			setDieColor(Color.black);
		}
    
		/** pre:		1 <= j <= 6
		 *  post:	dieRect has j spots added to it
		 */
		public void setSpotCount(int j) {
			assert 1 <= j && j <= 6 : "Invalid number of die spots";
			numberOfSpots = j;
			dieRect.removeAll();
			if (numberOfSpots == 1) {
				dieRect.add( middleSpot, 0 );
			} else if (numberOfSpots == 2) {
				dieRect.add( topLeftSpot, 0 );
				dieRect.add( botRightSpot, 0 );
			} else if (numberOfSpots == 3) {
				dieRect.add(  topLeftSpot, 0 );
				dieRect.add( middleSpot, 0 );
				dieRect.add( botRightSpot, 0 );
			} else if (numberOfSpots == 4) {
				dieRect.add( topLeftSpot, 0 );
				dieRect.add( botLeftSpot, 0 );
				dieRect.add( topRightSpot, 0 );
				dieRect.add( botRightSpot, 0 );
			} else if (numberOfSpots == 5) {
				dieRect.add( topLeftSpot, 0 );
				dieRect.add( botLeftSpot, 0 );
				dieRect.add( middleSpot, 0 );
				dieRect.add( topRightSpot, 0 );
				dieRect.add( botRightSpot, 0 );
			} else {
				dieRect.add( topLeftSpot, 0 );
				dieRect.add( midLeftSpot, 0 );
				dieRect.add( botLeftSpot, 0 );
				dieRect.add( topRightSpot, 0 );
				dieRect.add( midRightSpot, 0 );
				dieRect.add( botRightSpot, 0 );
			}
			dieRect.repaint();
			assert spotCountSameAsDotsAdded()
				: "Number of spots does not match spotCount()";
		}
    
		/** post:	result == numberOfSpots */
		public int spotCount()  {
			return numberOfSpots;
		}

		/** post:		dieRect.getBackground() == c
		 *			and  (dieRect.getBackground() == Color.white  
		 *				implies  all spots are colored black)
		 *			and  (dieRect.getBackground() != Color.white  
		 *				implies  all spots are colored white)
		 */
		public void setDieColor(Color c)  {
			dieRect.setBackground( c );
			if (c == Color.white) {
				setAllSpotColors(Color.black);
			} else {
				setAllSpotColors(Color.white);
			}
			dieRect.repaint();
			assert	implies( c == Color.white, 
						middleSpot.getBackground() == Color.black )
					&& implies( c != Color.white,
						middleSpot.getBackground() == Color.white )
				: "Color of die background inconsistent with spot color";
		}
    
		/** post:	result == dieRect */
		public Rectangle getDieRect() {
			return dieRect;
		}
        
		/** post:	result is a newly instantiated Oval
		 *			and  result.getX() == x  and  result.getY() == y
		 *			and  result.getWidth == result.getHeight == 10
		 *			and  result.getColor == Color.white
		 */
		private Oval newSpot(int x, int y)  {
			Oval result;
			result = new Oval(x, y, 10, 10);
			result.setBackground( Color.white );
			return result;
		}
    
		/** post:   result == p implies q */
		private boolean implies(boolean p, boolean q) {
			return !p || q;
		}
    
		/** post:	topLeftSpot.getBackground() == c
		 *			and  midLeftSpot.getBackground() == c  
		 *			and  botLeftSpot.getBackground() == c
		 *			and  middleSpot.getBackground() == c
		 *			and  topRightSpot.getBackground() == c
		 *			and  midRightSpot.getBackground() == c
		 *			and  botRightSpot.getBackground() == c
		 */
		private void setAllSpotColors(Color c ) {
			topLeftSpot.setBackground(c);
			midLeftSpot.setBackground(c);
			botLeftSpot.setBackground(c);
			middleSpot.setBackground(c);
			topRightSpot.setBackground(c);
			midRightSpot.setBackground(c);
			botRightSpot.setBackground(c);
		}
    
		/** post:	numberOfSpots == count of spots added to dieRect */
		private boolean spotCountSameAsDotsAdded()  {
			int dotsAddedCount = 0;
			if (topLeftSpot.getParent() != null)
				dotsAddedCount++;
			if (midLeftSpot.getParent() != null)
				dotsAddedCount++;
			if (botLeftSpot.getParent() != null)
				dotsAddedCount++;
			if (middleSpot.getParent() != null)
				dotsAddedCount++;
			if (topRightSpot.getParent() != null)
				dotsAddedCount++;
			if (midRightSpot.getParent() != null)
				dotsAddedCount++;
			if (botRightSpot.getParent() != null)
				dotsAddedCount++;
			return (dotsAddedCount == numberOfSpots); 
		}
}