Interviewer asked me why is 1 == 1 True but 1000 == 1000 False in Java?

The maddening truth about Java’s Integer caching and why it loves small numbers but betrays you at bigger ones.

I remember the first time I saw this in action.

I had just wrapped my head around autoboxing in Java and thought, “Great, I can treat primitives and objects almost the same. Life is good.”

And then, out of nowhere, my neat little test failed.

Integer a = 1000;
Integer b = 1000;
System.out.println(a == b); // false

Integer x = 1;
Integer y = 1;
System.out.println(x == y); // true

My reaction? Pure rage.

How the heck is 1 == 1 true but 1000 == 1000 false?

Isn’t equality supposed to be straightforward?

Spoiler: Java doesn’t care about your feelings. It cares about performance.

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The Great Betrayal: Autoboxing and Identity

Let’s get one thing straight: == on objects doesn’t check value equality—it checks reference equality.