Difference between final and effectively final

Question

I\'m playing with lambdas in Java 8 and I came across warning local variables referenced from a lambda expression must be final or effectively final. I know tha

Answer 1

public class LambdaScopeTest {
    public int x = 0;        
    class FirstLevel {
        public int x = 1;    
        void methodInFirstLevel(int x) {

            // The following statement causes the compiler to generate
            // the error "local variables referenced from a lambda expression
            // must be final or effectively final" in statement A:
            //
            // x = 99; 

        }
    }    
}

As others have said, a variable or parameter whose value is never changed after it is initialized is effectively final. In the above code, if you change the value of x in inner class FirstLevel then the compiler will give you the error message:

Local variables referenced from a lambda expression must be final or effectively final.

Answer 2

Effective final topic is described in JLS 4.12.4 and the last paragraph consists a clear explanation:

If a variable is effectively final, adding the final modifier to its declaration will not introduce any compile-time errors. Conversely, a local variable or parameter that is declared final in a valid program becomes effectively final if the final modifier is removed.