interfacetest.java

通过JAVA

public class InterfaceTest
{ public static void main(String args[])
  { double x;
    Circle y=new Circle(2.0);
    x=y.calculate_area();
    System.out.println("\nthe area is:"+x+"\n");
    }
}
interface Cal_area
{ double PI=3.14;
  double calculate_area();
}
class Circle implements Cal_area
{ double r;
  Circle(double r)
   {this.r=r;}
   public double calculate_area()
  {return PI*r*r;}
}