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

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 internalData;

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