CODEWITHSUNDEEP
javaoopinheritanceequals
Kyranstar
Kyranstar

Reputation: 1720

Overriding equals method

So I have a setup like this:

interface A{

}
class B implements A{
    public int hashCode() {
    ...
    }

    public boolean equals(final Object obj) {
    ...
    }
}
class C implements A{
    public int hashCode() {
    ...
    }

    public boolean equals(final Object obj) {
    ...
    }
}
class D{
    List<A> list = new ArrayList<A>();
}

I want to implement an overridden equals method for class D that tests that the lists are equal, but for some reason whenever I try to implement that as this:

@Override
    public boolean equals(final Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;

        final D other = (D) obj;
        if (values == null) {
            if (other.values != null)
                return false;
        }else if (!values.equals(other.values))
            return false;
        return true;
    }

but I believe that this calls Object's equals method where it calls values.equals(other.values), because it is not behaving correctly.

What can I do to make D's equals method behave correctly?

Upvotes: 0

Views: 125

Answers (5)

Gabriel Ruiu
Gabriel Ruiu

Reputation: 2803

Indeed, you need to override the equals such that you define a comparison factor between the actual lists.

If you use Maven for dependency management, here you can find Apache Commons Lang3 which contains a handy class called EqualsBuilder, very useful for overriding equals method.

Upvotes: 1

pratikch
pratikch

Reputation: 680

equals method is available from Object class. So it is available in all the concrete Java Classes. The signature of equals method is public boolean equals(Object equals).

Also, equals method should work in tandem with hashcode method for checking the equality. Its robust way for confirming.

Upvotes: 0

Drunix
Drunix

Reputation: 3343

Your last comparison should use Arrays.equals(list, ((D)other).list) to compare all array elements. Is VSequence actually D? Then you can drop the cast to D.

Upvotes: 0

Balayesu Chilakalapudi
Balayesu Chilakalapudi

Reputation: 1406

equals() is the predefined method which is belongs to Object class. Remember java is the Object oriented programming language which means that equals() method is applicable to every java class implicitely. you have not use the predefined method names as your custom methods.

Inorder to simulatte the equals() you need to change the signature, like this,

public boolean equals_simulation(final Object obj) {
   ...
}

Upvotes: 2

link
link

Reputation: 1676

If you are using an IDE such as Eclipse and you don't need to implement custom rules for equality, you can have Eclipse implement the method for you. Just look for the "override equals and hashCode" option. It should be under Source, or Source > refactor.

Upvotes: 1

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