Does removing the “final” keyword affect binary compatibility?

Question

If I remove the final keyword from a method or other "thing", will users of my class have to recompile?

Answer 1

Technically, they won't have to recompile.

I cannot think of any repercussions that can result from removing the final keyword from a method / attribute which may lead to loss in compatibility so it should not give you any problems.

Tested with sample code and there were no runtime errors:

public class Test2{
    public static final String test = "HELLO!";
}

public class Test {
    public static void main (String [] args) {
        System.out.println(Test2.test);
    }
}

1. Compiled Test.java
2. Ran Test.java -> Output = "HELLO!"

3. Modified Test2.java:

   public class Test2{
       public static String test = "HELLO!";
   }
   

4. Compiled Test2.java

5. Ran Test.java -> Output = "HELLO!"

Answer 2

No, removing the final keyword will not break compatibility assuming you're fine with this wart:

If module B calls any method from a class in module A and module C overrode the previously final method, and an object from module C is passed to module B, the call will go to module A's implementation.

Answer 3

No if your clients call your code directly. But is might break a program that discovers your class using reflection, checks whether your method is final and does different things if method is final or not.

Answer 4

Straight from the horse's mouth:

Changing a method that is declared final to no longer be declared final does not break compatibility with pre-existing binaries.

http://docs.oracle.com/javase/specs/jls/se7/html/jls-13.html#jls-13.4.17