What is the Java equivalent of C++'s const member function?

Question

In C++, I can define an accessor member function that returns the value of (or reference to) a private data member, such that the caller cannot modify that private data member in any way.

Is there a way to do this in Java?

If so, how?

I know about the final keyword but AFAIK, when applied to a method it:

1. Prevents overriding/polymorphing that method in a subclass.
2. Makes that method inline-able. (see comment by @Joachim Sauer below)

But it doesn't restrict the method from returning a reference to a data member so that it can't modified by the caller.

Have I overlooked something obvious?

Answer 1

There's no equivalent to the C const "type modifier" in Java (sadly).

The closest you can get is to return an immutable object or an immutable wrapper around a mutable object.

Immutability is not a language feature of Java, however, so you'll have to rely on Libraries.

Examples of immutable objects are:

• the primitive wrappers Integer, Character, ..
• String
• File
• URL

Commonly used immutable wrapper (i.e. wrappers around mutable types that prevent mutation) are those returned by the Collecton.unmodifiable*() methods.

Answer 2

This does not exist in java. final and const have different semantics, except when applied to a variable of a primitive type. The java solution typically involves creating immutable classes - where objects are initialized in construction and provide no accessors allowing change. Example of such classes would be e.g. String or Integer.