Distinguish Java Reference Equality from equals
Role: Software Engineer
Category: Software Engineering Fundamentals
Difficulty: medium
Interview Round: Technical Screen
What is the difference between == and equals() in Java? Explain reference comparison, primitive comparison, and how a class defines logical equality.
### What a Strong Answer Covers
Avoid describing object identity as a portable memory-address comparison. Explain Object's default equality, value-class overrides, null handling, and the hashCode obligation when equals is overridden.
### Follow-up Questions
- Why can two distinct String instances compare equal with equals but not ==?
- What can happen if a mutable field used by equals changes while the object is a hash-map key?
Overview: Explain Java identity comparison, logical equality, and null-safe comparisons. Connect equals to hashCode and show why mutable equality fields can make hash-map keys unreliable.