Question

If a String object is immutable (and thus obviously cannot change its length), why is length() a method, as opposed to simply being public final int length such as there is in an array?

Is it simply a getter method, or does it make some sort of calculation?

Just trying to see the logic behind this.

Answer 1

Java is a standard, not just an implementation. Different vendors can license and implement Java differently, as long as they adhere to the standard. By making the standard call for a field, that limits the implementation quite severely, for no good reason.

Also a method is much more flexible in terms of the future of a class. It is almost never done, except in some very early Java classes, to expose a final constant as a field that can have a different value with each instance of the class, rather than as a method.

The length() method well predates the CharSequence interface, probably from its first version. Look how well that worked out. Years later, without any loss of backwards compatibility, the CharSequence interface was introduced and fit in nicely. This would not have been possible with a field.

So let’s really inverse the question (which is what you should do when you design a class intended to remain unchanged for decades): What does a field gain here, why not simply make it a method?