Rules roundup (#95)

[Raghuveer Kumarakrishnan]

Hi ranchers,

I think the explanantion for #95 needs to be modified a little

The case argument must be a int literal or int-compatible variable which is a constant (i.e. static final)

I think it sould read "...which is a constant (i.e. final)"

static modifier is not necessary here

[Jeff Albertson]

public class Test {
    static final int A=1;
    final int B;
    static final int C;
 
    static {
        int total=0;
        for(int i=0; i<10; ++i)
            total+=i;
        C = total;
    }
 
    Test(int b) {
        this.B = b;
    }
 
    void f(int x) {
        switch(x) {
        case A:
        case B:
        case C:
        }
    }
}

[Raghuveer Kumarakrishnan]

Hi Jeff,

My point was not that static wont work but static is not needed just final would do .

static final int -- works
final int --works
--------------------------
=> final is needed,static optional
-----------------------------

[Ernest Friedman-Hill]

And Jeff's point is that you're wrong. Read the program he posted, then try to compile it.

[Jeff Albertson]

Originally posted by Raghu Kumar:

My point was not that static wont work but static is not needed just final would do .

You are right: "static" is not necessary, but "final" is not sufficient.
I went and looked up the definition in the JLS -- it's one of those things
that seems easy until you have to define it. It would seem that the
roundup question, if meant to be read as a definition, is too vague.

The definition states that the case expression must be a constant expression or an enum expression (for 1.5).
A constant expression may contain constant variables.
A constant variable is of primitive or string type, final and initialized
with a compile-time constant expression.

You are right, no mention of static.

[Jim Yingst]

Well, Jeff didn't say what his point was, but his program does not show that static is necessary. Rather, it shows that a constant must be initialized as it is declared, using an expression which is itself a compile-time constant expression. Note that in Jeff's program, neither B nor C can be used as case options. It doesn't matter that C is static - the problem is it's not initialized on declaration. Conversely, if we modify the declaration of A to remove the "static", it still works fine. Being static is not necessary to be an option in a switch statement.

It would be true to say that there's no reason not to make such a variable static. Being final and also initialized on declaration with a compile-time constant means there's no possible way different instances would have different values. So I would certainly recommend making the variable static, for clarity if nothing else.

[Jim Yingst]

Obviously I saw Jeff's second post after writing the above, but I'll leave my post as is, as it has some supplemental discussion.

[Raghuveer Kumarakrishnan]

  
public class MySwitch 
{
  public static void main(String[] args) 
  {
     final int THIS_WORKS=30;
     short s= 30;
     switch(s)
     {
case 1:
   System.out.println("Governator sucks");
   break;
case THIS_WORKS:
   System.out.println("Final is sufficient");
   break;
        default:
     }
 
   }
}

[Raghuveer Kumarakrishnan]

Jeff,Ernest and Jim, thanks for the clarifications.

[ November 17, 2005: Message edited by: Raghu Kumar ]
[ November 17, 2005: Message edited by: Raghu Kumar ]