import static java.lang.System.out; public class S

问答题

import static java.lang.System.out;
public class ShapeDemo{
public static void main(String[] args){
Shape shape=new Circle(5);
out.println(shape.area());
}
}
interface Shape{
;
}
class Circle implements Shape{
private double r;
public Circle(double _r){
this.r=_r;
}
@Override public double area(){
return Math.PI*r*r;
}
}

【参考答案】

double area()