Constant values in switch/case

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Wojtek Bok - 08 Jun 2005 17:20 GMT

If I set up a class definition with:

------------------------------
public static final int SORT_FIRST_NAME = 0;
public static final int SORT_LAST_NAME = 1;
public static final int SORT_BIRTHDAY = 2;
------------------------------

then use this in a switch clause:

------------------------------
switch(sortOrder)
{
case SORT_FIRST_NAME:
// do work
case SORT_LAST_NAME:
// do work
case SORT_BIRTHDAY:
// do work
}
------------------------------

all is well. But, if I use dynamic allocation:

------------------------------
private static int cvCounter = 0;
public static final int SORT_FIRST_NAME = cvCounter++;
public static final int SORT_LAST_NAME = cvCounter++;
public static final int SORT_BIRTHDAY = cvCounter++;
------------------------------

then the switch/case statements show errors (in Eclipse 3.02).

Why? Eclipse accepts the value assignment. And the values ARE final, yet
the switch/case shows an error that "case expressions must be constant
expressions".

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James Korman - 09 Jun 2005 00:54 GMT

>If I set up a class definition with:
>
[quoted text clipped - 32 lines]
>the switch/case shows an error that "case expressions must be constant
>expressions".

Your assignment is legal. But doesn't qualify as a constant expression

See the LRM 15.28 Constant Expression

A compile-time constant expression is an expression denoting a value
of primitive type or a String that is composed using only the
following:
...
* The unary operators +, -, ~, and ! (but not ++ or --) <<<<
...

Jim

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Wojtek Bok - 09 Jun 2005 16:05 GMT

>>------------------------------
>>private static int cvCounter = 0;
[quoted text clipped - 19 lines]
> * The unary operators +, -, ~, and ! (but not ++ or --) <<<<
> ...

Ah ok, now I understand. The constant expression must be constant at
compile time, yet the values are not known until the class is first
instantiated.

Thanks.

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Constant values in switch/case

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