A friend of mine has been recently interviewed by Google and they asked him to write an Immutable class.

I didn’t even know they asked such stupid basic questions on Google interviews but for those of you who don’t remember what an immutable object is, it’s just an object that cannot be modified after its creation, such as a, guess what? String!

When you do:

String example = “Example”;

You just created an immutable object. Every operation to that object will create a new String, you won’t ever modify it.

So to write a class for immutable objects you just need not to provide a way to modify it.


class ImmutableObject {

}


As you see, you can only assign a value to ‘value’ at construction. On the other hand, if you had a


public void setValue(int valueToUseNow) {
value = valutToUseNow;
}


Then you could change ‘value’ after construction and this class now would be mutable.