HashSet<interface>

[Jose Rguez]

Hello:

Is inhering from a common interface (like I coded below) the best and orthodox way of create a HashSet<...> of objects of different classes?


Thanks in advance,

import java.util.*;

interface Inter {
        int getI();
        int getInd();
}

class A implements Inter {
        private static int count;
        private int i;
        private int ind;
        A(int i) {
                this.i = i;
                ind = count++;
        }
        public String toString() {
                return "(A) i: " + i + ", ind: " + ind + ", hashCode: " + hashCode();
        }
        @Override
        public int getI() {
                return i;
        }
        @Override
        public int getInd() {
                return ind;
        }
        @Override
        public int hashCode() {
                return i;
        }
        @Override
        public boolean equals(Object o) {
                return i == ((Inter)o).getI() && ind == ((Inter)o).getInd();
        }
}

class B implements Inter {
        private static int count;
        private int i;
        private int ind;
        B(int i) {
                this.i = i;
                ind = count++;
        }
        public String toString() {
                return "(B) i: " + i + ", ind: " + ind + ", hashCode: " + hashCode();
        }
        @Override
        public int getI() {
                return i;
        }
        @Override
        public int getInd() {
                return ind;
        }
        @Override
        public int hashCode() {
                return i;
        }
        @Override
        public boolean equals(Object o) {
                return i == ((Inter)o).getI() && ind == ((Inter)o).getInd();
        }
}

class Ov {
        public static void main(String... arg) {
                HashSet<Inter> set = new HashSet<Inter>();
                A a1 = new A(1);
                A a2 = new A(1);
                B b1 = new B(1);
                B b2 = new B(1);

                set.add(a1);
                set.add(a2);
                set.add(b1);
                set.add(b2);
                for (Object o : set) {
                        System.out.println(o);
                }
        }
}

/*
Output:
(A) i: 1, ind: 1, hashCode: 1
(A) i: 1, ind: 0, hashCode: 1
*/

[Jeanne Boyarsky]

Yes, that is an appropriate way of mixing objects in a collection/set. Obviously, the interface should have something common - you do have those two methods so it works.