java泛型类的定义与使用

[Vic-Tory]

我在学习java泛型类时遇到了这样一个问题：定义了两个基本类圆形（Circle）、长方形（Rectangle），定义一个泛型类体积（Volume），我希望通过Volume类可以实现对底面积为圆、长方形求体积，应该怎样在Volume类中获取Circle或者Rectangle的面积呢？

package ex9.generalclass;

import java.text.DecimalFormat;

public class GeneralClass {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Circle c1=new Circle(3.5);
		Volume<Circle> c1v=new Volume<Circle>(c1,2.5);
		c1v.showVolume();
	}

}
class Circle{//圆形
	final double PI=3.14159;
	private double radius;
	
	public Circle(double radius){
		this.radius=radius;
	}
	public double getArea(){
		return PI*radius*radius;
	}
}

class Rectangle{//长方形
	private double length,width;
	
	public Rectangle(double length,double width){
		this.length=length;
		this.width=width;
	}
	public double getArea(){
		return length*width;
	}
}

class Volume<E>{//体积泛型
	E area;
	private double height;
	
	public Volume(E area,double height){
		this.area=area;
		this.height=height;
	}
	public void showVolume(){
		DecimalFormat DF=new DecimalFormat("#.##");
		System.out.println("体积为"+
		DF.format(1/3*area.getArea()*height)));//这里应该怎样获取底面积？
	}
}

[繁华终归落尽]

public class GeneralClass {
	public static void main(String[] args) {
        // TODO Auto-generated method stub
        Circle c1=new Circle(3.5);
        Volume<Circle> c1v=new Volume<Circle>(c1,2.5);
        c1v.showVolume();
    }
}

abstract class HasArea{
	public abstract double getArea();
}

class Circle extends HasArea{//圆形
    final double PI=3.14159;
    private double radius;
     
    public Circle(double radius){
        this.radius=radius;
    }
    
    @Override
    public double getArea(){
        return PI*radius*radius;
    }
}
 
class Rectangle extends HasArea{//长方形
    private double length,width;
     
    public Rectangle(double length,double width){
        this.length=length;
        this.width=width;
    }
    
    @Override
    public double getArea(){
        return length*width;
    }
}
 
class Volume<E extends HasArea>{//体积泛型
    E area;
    private double height;
     
    public Volume(E area,double height){
        this.area=area;
        this.height=height;
    }
    public void showVolume(){
        DecimalFormat DF=new DecimalFormat("#.##");
        System.out.println("体积为"+
        DF.format(area.getArea()*height));//这里应该怎样获取底面积？
    }
}

简单改了一下，看看是不是你需要的

[强迫症专用头像]

楼上正解，HasArea最好写成interface