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

Answer 1

One way to avoid this issue is to no expose the data structure (another is returning a copy, or an immutable wrapper)

e.g. instead of

public List<String> getSomeList();

have

public String getSomeElement(int index);

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.

Answer 3

You haven't overlooked anything. There is no way in pure Java to do so. There might be libraries which provide some subset of this using annotations, but I don't know any offhand.

The way you pass back a reference to immutable data is to make the class you pass back immutable, plain and simple. There are a couple of library functions to help you produce an immutable view of some data in some very limited but common cases. Here's one example:

private List<String> internalData;

public List<String> getSomeList() {
    return Collections.unmodifiableList(internalData);
}