Question

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Overriding equals and hashCode in Java

I am supposed to implement hashcode and equals for Custom class Person. Person consists of

firstname

lastname

I am supposed to implement equals and hashcode such that two people with firstname and lastname should return true for equals and should be accepted by Hashmap. I have implemented Person class like this:

public class Person {


    String firstname;
    String lastname;
    public Person(String firstname, String lastname) {
        this.firstname = firstname;
        this.lastname = lastname;
    }

    @Override
    public int hashCode() {
        // TODO Auto-generated method stub
        return firstname.hashCode()+lastname.hashCode();
    }

    @Override
    public boolean equals(Object obj) {
        // TODO Auto-generated method stub
    Person u=(Person) obj;

        return u.firstname.equals(firstname) && u.lastname.equals(lastname);
    }

}

Is the implementation of Hashcode correct here? Even though I am getting the expected result,I want to know if this implementation is correct?

Answer 1

There is a slight problem with your equals method because it will throw an exception if obj is null or not a Person, so you should add the following to the top of your equals:

if(obj==null || !(obj instanceof Person))
   return false;