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); }}