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

I don't think there is a way to that in Java for non primitive objects (you're always passing around references to such objects). The closest you could do would be to return a copy of the object (using clone or something like that) ; but that would not be very idiomatic Java.

I you want to give access only to the 'visible' part of a member object, what you could do is create an interface with the visible part, and return this interface. For example :

public interface Bar {
     public int getBing();
}

public class BarImpl implements Bar {
     private int bing;
     public int getBing() {
        return bing;
     }
     public void setBing(int bing) {
        this.bing = bing;
     }
}

public class Foo {
     private BarImpl bar;

     public Bar getNonModifiableBar() {
         return bar; // Caller won't be able to change the bing value, only read it.
     }
}