Java Interfaces - Exercise

Creating Interfaces in Java

Instructions

interface Enclosure {
  public double perimeter();
  public double area();
}

class Circle {
  double radius;
  Circle(double radius) {
    this.radius = radius;
  }
 }

class Square {
  double width;
  Square(double width) {
    this.width = width;
  }
 }

class EnclosureTest {
  public static void main(String[] args) {

    Enclosure[] enclosures = new Enclosure[2];
    enclosures[0] = new Circle(5.0);
    enclosures[1] = new Square(10.0);
    for (int n = 0; n < enclosures.length; n++)
      System.out.println("area = " +
      enclosures[n].area() +", perimeter = " + 
      enclosures[n].perimeter());
  }
}

Hints

1. The constant PI is defined in the Math class (Math.PI).
2. When you run EnclosureTest here are the results you should observe:
   

   area = 78.53981633974483, perimeter = 31.41592653589793
   area = 100.0, perimeter = 40.0
   

Source Files

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