定义类Shape表示一般二维图形。Shape具有抽象方法area和perimeter，分别计算形状的

publicabstractdoublearea();
publicabstractdoubleperimeter();
}
classRectangleextendsShape{//矩形
privatedoublewide;//宽
privatedoublelongs;//长
publicRectangle(){
}
publicRectangle(doublewide,doublelongs){
super();
this.wide=wide;
this.longs=longs;
}
publicdoublearea(){
returnthis.longs*this.wide;
}
publicdoubleperimeter(){
return(this.longs+this.wide)*2;
}
}
classTriangleextendsShape{//三角形
privatedoubleedgea;//边长
privatedoubleedgeb;//边长
privatedoubleedgec;//边长
publicTriangle(){
}
publicTriangle(doubleedgea,doubleedgeb,doubleedgec){
super();
this.edgea=edgea;
this.edgeb=edgeb;
this.edgec=edgec;
}
publicdoublearea(){
returnthis.edgea*this.edgeb/2;
}
publicdoubleperimeter(){
returnthis.edgea+this.edgeb+this.edgec;
}
}
classRoundextendsShape{//圆形
privatedoubleradius;//半径
publicRound(){
}
publicRound(doubleradius){
super();
this.radius=radius;
}
publicdoublearea(){
returnthis.radius*this.radius*Math.PI;
}
publicdoubleperimeter(){
returnthis.radius*2*Math.PI;
}
}
publicclassTestDemo{
publicstaticvoidmain(Stringargs[]){
Shaperectangle=newRectangle(10.5,20.6);
Shapetriangle=newTriangle(10.1,20.2,30.3);
Shaperound=newRound(30.3);
System.out.println("矩形面积："+rectangle.area()+"，矩形周长："+rectangle.perimeter());
System.out.println("三角形面积："+triangle.area()+"，三角形周长："+
triangle.perimeter());
System.out.println("圆形面积："+round.area()+"，圆形周长："+round.perimeter());
}
}