== for Primitives vs Objects in Java

Q: == for Primitives vs Objects in Java

With two primitive operands, `==` compares the primitive values after any required numeric promotion. With two reference operands, it checks whether both references are `null` or denote the same object. For example, two separate `String` objects can contain `"hello"` yet be unequal by `==`.

Beginner·2 min read·

TcsInfosysWiproAmazonMicrosoft

Fast recall

Quick revision

Core answer

With two primitive operands, == compares the primitive values after any required numeric promotion. With two reference operands, it checks whether both references are null or denote the same object. For example, two separate String objects can contain "hello" yet be unequal by ==.

Interview-ready guide

Interview answer

For primitives, == compares values. For example, int a = 5; long b = 5L; makes a == b true after Java promotes the int for the numeric comparison. It does not compare where a primitive is stored.

For references, == asks an identity question: do these references denote the same object, or are both null? If String first = new String("hello") and String second = new String("hello"), then first == second is false because they are separate objects. first.equals(second) is true because String defines equality by character content.

So I choose the comparison from the operand type and the question being asked. I use == for primitive values and when reference identity is intentional. I use a class's equality method for logical value comparison, while remembering that a class which does not override Object.equals() still has identity-based equality.

03 · Deep dive