1．定义一个抽象类Shape，包含求面积area和周长perimeter的两个函数。定义圆Circle类，继承Shape类。(java

Question

帮帮忙，作业！

Answer 1

package example5;

abstract class Shape
{
abstract double area();
abstract double perimeter();
}

class _Circle extends Shape
{
double radius;
_Circle(double r)
{
radius = r;
}
public double area()
{
return Math.PI * radius * radius;
}
public double perimeter()
{
return 2*Math.PI *radius;
}
}
class _Triangle extends Shape
{
double length1,length2,length3;//三角行三条边长度
_Triangle(double l1,double l2,double l3)
{
length1 = l1;
length2 = l2;
length3 = l3;
}
public double area()
{
double p = 1.0/2*(length1+length2+length3);
return Math.sqrt(p*(p-length1)*(p-length2)*(p-length3));
}
public double perimeter()
{
return 1.0/2*(length1+length2+length3);
}
}
class _Rectangle extends Shape
{
double length1,length2;
_Rectangle(double l1,double l2)
{
length1 = l1;
length2 = l2;
}
public double area()
{
return length1*length2;
}
public double perimeter()
{
return 2*(length1+length2);
}
}
public class LX_6_1 {

/**
* @param args
*/
public static void main(String[] args) {
// TODO 自动生成方法存根
_Circle c = new _Circle(2);
_Triangle t = new _Triangle(3,4,5);
_Rectangle r = new _Rectangle(4,5);
System.out.println("圆的面积为："+c.area()+",圆的周长为："+c.perimeter());
System.out.println("三角形的面积为："+t.area()+",三角形的周长为："+t.perimeter());
System.out.println("长方形的面积为："+r.area()+",长方形的周长为："+r.perimeter());
}
}
因为我之前的类中有了Circle类，所以我在前面加了_。。你可以把类名前面的_去掉。。