Is it possible to make an object “Read Only” to a method

Question

If an object reference is passed to a method, is it possible to make the object \"Read Only\" to the method?

Answer 1

Expanding on ewernli's answer...

If you own the classes, you can use read-only interfaces so that methods using a read-only reference of the object can only get read-only copies of the children; while the main class returns the writable versions.

example

public interface ReadOnlyA {
    public ReadOnlyA getA();
}

public class A implements ReadOnlyA {
    @Override
    public A getA() {
        return this;
    }

    public static void main(String[] cheese) {
        ReadOnlyA test= new A();
        ReadOnlyA b1 = test.getA();
        A b2 = test.getA(); //compile error
    }
}

---

If you don't own the classes, you could extend the class, overriding the setters to throw an error or no-op, and use separate setters. This would effectively make the base class reference the read-only one, however this can easily lead to confusion and hard to understand bugs, so make sure it is well documented.