simpleclassdemo5.java

JAVA程序设计课程中各章节的程序实例。

/**
*A override program of polymorphism demonstration
* it's a simple but classical example
*2005.1.10. xhcprince
*/

class Shape
{
	String name = "";
	final static double pi = 3.1415926;
	
	public void area()
	{
		System.out.println("Shaape class:no area defined!");
	}
}

class Rectangle extends Shape
{
	double length,
		   width;
		   
    Rectangle(double len, double wid)
    {
    	length = len;
    	width = wid;	
    }
	
	public void area()
	{
		double area = length*width;
		
		System.out.println("Shape name: " + name);
		System.out.println("Shape area: " + area);
	}
}

class Circle extends Shape
{
	double radius;
	
	Circle(double r)
	{
		radius = r;
	}
	
	public void area()
	{
		double area = radius*radius*pi;
		
		System.out.println("Shape name: " + name);
		System.out.println("Shape area: " + area);
	}
}

public class simpleClassDemo5
{
	public static void main(String args[])
	{
		Shape rect = new Rectangle(3.7,4.2);	//pay attention to the constructor!
		Shape cirl = new Circle(1.1);
		
		rect.name = "Rectangle";
		cirl.name = "Circle";
		
		rect.area();
		cirl.area();
	}
}
/**
*We create the objects of Shape (not Rectengle and Circle! pay attention here),and instantiate it with the objects
* of it's subclasses (Rectanblew andd Circle).When we call the area function,the polymorphism comes into play
* The compiler at the time of compliation does not now in advance which area() function to call,this ambiguity is
* resolved at the run time.
*/