Question

I know that based on the Java tutorials:

An interface can contain constant declarations in addition to method declarations. All constant values defined in an interface are implicitly public, static, and final. Once again, these modifiers can be omitted.

Is it possible to make the values inside an interface to be shared and modifiable by all the classes that implement the said interface?

Answer 1

In theory, yes, if you use a mutable type for your “constant”, e.g. AtomicReference.
However, it would be an awful design!

public interface MyInterface{
    AtomicReference<String> NAME = new AtomicReference<String>("Fred");
}


public static void main(final String[] args){
    System.out.println(MyInterface.NAME);
    MyInterface.NAME.set("Jim");
    System.out.println(MyInterface.NAME);
}

Output:

Fred
Jim

You could use Collections, Maps, Arrays or any other type that mutably holds values for this pattern, however I would seriously request you to rethink it.