final keyword preceding the parameter declaration in method declaration

Question

class hello {
    public static void main(String arg[]){

    int[] c = { 2 };
    final int[] d = { 3 };

    }

static void useArgs(final int a, int b, final int[] c, int[] d) {

    c[0]=d[0]; // no error 
    c = d; //error 
    }
 }

guys can anybody can explain this behavior?

http://stackoverflow.com/questions/5380177/final-arguments-in-interface-methods-whats-the-point — BobTheBuilder, Mar 10 '13 at 06:42
http://stackoverflow.com/questions/4930114/why-declare-a-function-argument-to-be-final — BobTheBuilder, Mar 10 '13 at 06:43

score 6 · Accepted Answer · answered Mar 10 '13 at 06:44

6

Variable c is final. Which means that you cannot assign another value to that variable.

But the elements in the array itself are not final, which is why you are able to change the assignment on the elements like c[0]=d[0].

answered Mar 10 '13 at 06:44

Thihara

7,031
2
29
56

Note that arrays (even arrays of primitives) are objects in Java. Objects are handled via a reference, and if the 'final' keyword is applied only the reference to the object is final, not the object's members. – Adriaan Koster Mar 10 '13 at 09:01

score 3 · Answer 2 · answered Mar 10 '13 at 06:42

3

c is a final (const) reference to an array of ints. and since c is final you cannot change its value (i.e change the address it refers to). And this goes for any variable declared as final (not just arrays).

This also won't work :

final int c = 1;
int d = 2;
c = 2; // Error
c = d; // Error

answered Mar 10 '13 at 06:42

giorashc

13,691
3
35
71

means it cannot change the **reference** value of c but the value of the array can be changed ? – gursahib.singh.sahni Mar 10 '13 at 06:44
c[0] != c and so the final is applied only for c itself and not its elements – giorashc Mar 10 '13 at 06:48
1

@anonymous: In the question, `c` is a *reference*. Its "value" is an address. It *points* to an array object. – newacct Mar 10 '13 at 10:39

final keyword preceding the parameter declaration in method declaration

2 Answers2