代码如下：
class Trangle
{
double sideA,sideB,sideC,area,length;
boolean boo;
public Trangle(double a,double b,double c)
{
sideA=a;
sideB=b;
sideC=c;
if(sideA+sideB>sideC&&sideB+sideC>sideA&&sideA+sideC>sideB)
{
boo=true;
}
else
{
boo=false;
}
}
double getLength()
{
length=sideA+sideB+sideC;
return length;
}
public double getArea()
{
if(boo)
{
double p=(sideA+sideB+sideC)/2.0;
area=Math.sqrt(p*(p-sideA)*(p-sideB)*(p-sideC));
return area;
}
else
{
System.out.println("不是一个三角形，不能计算面积");
return 0;
}
}
public void setABC(double a,double b,double c)
{
sideA=a;
sideB=b;
sideC=c;
if(sideA+sideB>sideC&&sideB+sideC>sideA&&sideA+sideC>sideB)
{
boo=true;
}
else
{
boo=false;
}
}
}
class Lader{
double above,bottom,heigh,area;
Lader(double a,double b,double h){
above=a;
bottom=b;
heigh=h;
}
double getArea(){
area=heigh*(above+bottom)/2.0;
return area;
}
}
class Circle{
double radius,area;
Circle(double r){
radius=r;
}
double getArea(){
area=3.14*radius*radius/2.0;
return area;
}
double getLength(){
return 2*3.14*radius;
}
void setRadius(double newRadius){
radius=newRadius;
}
double getRadius(){
return radius;
}
}
public class AreaAndLength{
public static void mian(String args[]){
double length,area;
Circle circle=null;
Trangle trangle;
Lader lader;
circle=new Circle(10.0);
trangle=new Trangle(3.0,4.0,5.0);
lader=new Lader(3.0,4.0,10.0);
length=circle.getLength();
System.out.println("圆的周长："+length);
area=circle.getArea();
System.out.println("圆的面积："+area);
length=trangle.getLength();
System.out.println("三角形的周长："+length);
area=trangle.getArea();
System.out.println("三角形的面积："+area);
area=lader.getArea();
System.out.println("梯形的面积："+area);
trangle.setABC(12.0,34.0,1.0);
area=trangle.getArea();
System.out.println("三角形的面积："+area);
length=trangle.getLength();
System.out.println("三角形的周长："+length);
}
}