How to maintain only non-equal object in HashSet

Question

How can i remove objects having the same state.

          class Student{
                private int age;
                private String name;

                Student(int age, String name){
                  this.age=age;
                  this.name=name;
               } }

              public class SetTest {
               public static void main(String[] args) {
            Student s1= new Student(15,"abc");
            Student s2= new Student(15,"abc");
            Student s3= new Student(16,"adfc");
            Student s4= new Student(14,"ayuc");

                Set<Student> ss= new HashSet<Student>();
                ss.add(s1); ss.add(s2); ss.add(s3); ss.add(s4);}}

here s1 and s2 are having equal state and as i am using Set and I want to keep only one instance. What should i do to take only object with non-equal instance.

Implement the `equals()` and `hashCode()` methods. – Sotirios Delimanolis Dec 04 '13 at 04:03 — Sotirios Delimanolis, Dec 04 '13 at 04:03

score 3 · Answer 1 · edited May 23 '17 at 11:49

3

You need to override the equals() and hashCode() methods in the Student class. In this method you define what it means for 2 students to be equal.

   @Override
   public boolean equals(Object other){
       //code to determine if this student is equal to other

   }

    @Override
    public int hashCode() {
       //code to generate a hashCode for the student
    }

Pay attention to the advice in this question.

edited May 23 '17 at 11:49

Community

1
1

answered Dec 04 '13 at 04:04

Vincent Ramdhanie

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Changed to upvote, the "advice in this question" bit is critical. – Taylor Dec 04 '13 at 04:11

score 1 · Answer 2 · answered Dec 04 '13 at 04:04

You need to override the equals() and hashCode() methods in your Student class.

class Student {
    ...
    @Override
    public boolean equals(Object obj) {
        // Your own logic
        // return super.equals(obj); // default
    }

    @Override
    public int hashCode() {
        // Your own logic
        // return super.hashCode(); // default
    }
}

How to maintain only non-equal object in HashSet

2 Answers2