example03_interface.java

java课程设计教材上的程例题序代码

package example;

/* 接口示例 */

interface CalculateArea
{
	/*public abstract*/ double getArea();
}


class Trapezia implements CalculateArea
{
	double top, bottom, height;
	
	Trapezia(double top,double bottom,double height)
	{
		this.top = top;
		this.bottom = bottom;
		this.height = height;
	}
	
	public final double getArea()
	{
		return (top + bottom) * height / 2.0;
	}
}


class Triangle implements CalculateArea
{
	double a, b, c;
	
	Triangle(double aSide,double bSide,double cSide)
	{
		a = aSide;
		b = bSide;
		c = cSide;
	}
	
	public double getArea()
	{
		double s = (a + b + c) / 2.0;
		
		return Math.sqrt((s * (s - a) * (s - b) * (s - c)));
	}
}


class Circle implements CalculateArea
{
	double r;
	
	Circle(double radius)
	{
		r = radius;
	}
	
	public double getArea()
	{
		return Math.PI * r * r;
	}
}


class Taper
{
	CalculateArea	bottArea;
	double	height;
	
	Taper(CalculateArea bottArea,double h)
	{
		this.bottArea = bottArea;
		height = h;
	}
	
	double getVolume()
	{
		return bottArea.getArea() * height / 3.0;
	}
}

public class Example03_Interface
{
	public static void main(String[] args)
	{
		CalculateArea ca;
		
		ca = new Trapezia(10, 10, 10);
		System.out.println("Trapezia Area=" + ca.getArea());
		
		ca = new Triangle(3, 4, 5);
		System.out.println("Triangle Area=" + ca.getArea());
		
		ca = new Circle(10);
		System.out.println("Circle Area=" + ca.getArea());
		
		Taper taper = new Taper(ca, 10);
		System.out.println("Trapezia Volume=" + taper.getVolume());
	}
}