java 实验 3

public class InterfaceTest {
public static void main(String args[]){
 double x;
 circle y=new circle(2);
 x=y.calculatearea();
 System.out.println("\n 面积为："+x+"\n");
}
}

interface calarea
{
 double PI=3.14;
 double calculatearea();
}

class circle implements calarea{
 double r;
 circle(double r)
 {
  this.r=r;
 }
 public double calculatearea()
 {
  return PI*r*r;
 }
}