nestedcircles.java

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

// Figure 6.14

import java.awt.Color;
/**	Class Invariant
 *		A NestedCircles object...
 *			is a filled circular region, possibly with black, 
 *			concentric circles upon it  
 */
public class NestedCircles  {
	private Oval initialOval;
	private int lastCircleRadius;

	/** pre:	r > 0   <br>
	 *	post:	A new black filled NestedCirle object is created 
	 *				with upper-left corner at (x, y)   
	 *			and  lastCircleRadius == r   
	 */
	public NestedCircles(int x, int y, int r)  {
		initialOval = new Oval(x, y, 2*r, 2*r);
		lastCircleRadius = r;
	}

	/** post:	result is this image suitable for passing as 
	 *			an argument to add.  */
	public Oval addableContent()   {
		return initialOval;
	}

	/** pre:	c is a valid Color  <br>
	 *	post:	initialOval is recolored using color c   
	 */
	public void setBackground(Color c)   {
		initialOval.setBackground(c);
		initialOval.repaint();
	}

	/** post:	lastCircleRadius == 0.8* lastCircleRadius@pre 
	 *			and  a black circle with radius  of lastCircleRadius is
	 *				 	added concentrically to this object 
	 */
	public void insertCircle()   {
		Oval newOval, circleCenter;
		int newX;
		lastCircleRadius = (int)(lastCircleRadius *.8);
		newX = (initialOval.getWidth() - 2*lastCircleRadius) / 2;
		newOval = new Oval(newX, newX, 
									2*lastCircleRadius, 2*lastCircleRadius);
		initialOval.add(newOval, 0);
		circleCenter = new Oval(1, 1, newOval.getWidth()-2,
										 newOval.getHeight()-2);
		circleCenter.setBackground( initialOval.getBackground() );
		newOval.add(circleCenter, 0);
		newOval.repaint();
	}
}