Equality and identity

While the == operator in Java compares references for identity, in Kotlin it is internally converted to a call of the equals method. The check for identity is possible with the new === operator (3x =).

One thing that probably most of us used to do wrong in the beginning is how to handle the == operator in Java.

Contradicting the intuition of many, it does not compare the content to which the compared references refer but their actual values ​​(read: memory addresses).

Instead, in Java, the equals method is required to check the referenced content for equality.

Even if you’ve gotten used to it, Kotlin reminds you that using == for the structural comparison (equals) is actually cleaner and more sensible than just comparing the references.

Kotlin turns == into equals

So Kotlin internally converts == to the call of equals.

This means that in Kotlin you check instances with == for structural equality instead of identity, as in Java.

As a consequence, you will only rarely encounter the call of equals written out in Kotlin code, but rather the more intuitive and readable == operator.

If you want to check two references for identity, Kotlin offers the operator === (3x =), which does just that.