Unique custom class values ​​in Java Set

Question

I expect to have only 2 elements in mine Set, but when printing I get 3 elements! How to determine uniqueness?

public class test {

    public static void main(String[] args) {

        class bin {
            int a;
            int b;
            bin (int a, int b){
                this.a=a;
                this.b=b;
            }
            public boolean Equals(bin me) {
                if(this.a==me.a && this.b==me.b)
                    return true;
                else 
                    return false;
            }   
            @Override
            public String toString() {
                return a+" "+b;
            }
        }

        Set<bin> q= new HashSet<bin>();
        q.add(new bin(11,23));
        q.add(new bin(11,23));
        q.add(new bin(44,25));

        System.out.println(q);
    }
}

Answer 1

There are two problems here.

• equals must be lowercase and accept Object
• You must also override hashCode

The modified code may look as follows. Please note that the implementation is far from perfect, as equalsyou need to check the null value and whether type creation is possible. Also hashCode, this is just an example, but how to implement such things is another topic.

import java.util.Set;
import java.util.HashSet;

public class test {

    public static void main(String[] args) {

        class bin{
            int a;
            int b;
            bin (int a, int b){
                this.a=a;
                this.b=b;
            }

            @Override
            public boolean equals(Object me) {
                bin binMe = (bin)me;
                if(this.a==binMe.a && this.b==binMe.b)
                    return true;
                else 
                    return false;
            }   

            @Override
            public int hashCode() {
                return this.a + this.b;
            }

            @Override
            public String toString() {
                return a+" "+b;
            }
        }

        Set<bin> q= new HashSet<bin>();
        q.add(new bin(11,24));
        q.add(new bin(11,24));
        q.add(new bin(10,25));
        q.add(new bin(44,25));

        System.out.println(q);
    }
}

---

Result:

[11 24, 10 25, 44 25]