接口对象的实例化在接口回调中的使用方法

interfaceComputerable

{

publicdoublearea();

}

classRecimplementsComputerable

{

doublea,b;

Rec(doublea,doubleb)

{

this.a = a;

this.b = b;

}

publicdoublearea() {

return(a*b);

}

}

classCircleimplementsComputerable

{

doubler;

Circle(doubler)

{

this.r = r;

}

publicdoublearea() {

return(3.14*r*r);

}

}

classVolume

{

Computerable bottom;

doubleh;

Volume(Computerable bottom,doubleh)

{

this.bottom = bottom;

this.h = h;

}

publicvoidchangeBottome(Computerable bottom)

{

this.bottom = bottom;

}

publicdoublevolume()

{

return(this.bottom.area()*h/3.0);

}

}

publicclassInterfaceRecall {

publicstaticvoidmain(String[] args)

{

Volume v =null;

Computerable bottom =null;

//借口变量中存放着对对象中实现了该接口的方法的引用

bottom =newRec(3,6);

System.out.println("矩形的面积是："+bottom.area());

v =newVolume(bottom,10);

//体积类实例的volum方法实际上计算的是矩形的体积，下同

System.out.println("棱柱的体积是："+v.volume());

bottom =newCircle(5);

System.out.println("圆的面积是："+bottom.area());

v.changeBottome(bottom);

System.out.println("圆柱的体积是："+v.volume());

}

}