Constants and static final Wrapper Objects

[Abimaran Kugathasan]

Can we use a static final wrapper object as a constant in java? If not, reasons Please? Thanks in Advanced!

[Raju Champaklal]

i surely want to know the answer for that....because i think you cant use them as a constant....but want to know why....

[Abimaran Kugathasan]

yaaa.... It's true, we can't use it. But don't know the reason

[rushikesh sawant]

my reasoning to this is..., when the compiler unwraps the wrapper object, what we get is only a mere value held by that wrapper object of particular type and it might not be coming out with its "static" and "final" flags turned on. and since compiler seeks constant expressions, it flags error.

this is what i think, i'm also a learner.

[Nidhi Sar]

Abimaran Kugathasan wrote:Can we use a static final wrapper object as a constant in java?

Abimaran,

When you say "use... as a constant" whcih statements are you talking about?

Thanks,
Nidhi

[Neha Daga]

well I agree with Rushikesh.
Wrappers are still objects refering to some primitive values and the modifiers static and final are for the wrapper object not the primitive.
So as rushikesh said when the primitive is unwrapped ther is no static or final modifier attached to it.

[Raju Champaklal]

did i really clear scjp? how did i clear it? i know nothing

[Abimaran Kugathasan]

So we cannot use it in Interfaces? Please confirm?

[Neha Daga]

Abimaran Kugathasan wrote:So we cannot use it in Interfaces? Please confirm?

you mean declare?
we can declare wrapper objects in interfaces but can use them as constants in the classes that implement those intefaces.

[Abimaran Kugathasan]

yaa, but declare and initialize it within an Interface.

[Vinay Dinakar]

Can you explain with an example. i can declare like this , static final Integer i=20;

[Jacob Sonia]

Use as constants means:

if you try to use a wrapper object in a switch loop as one of the case value, it would fail and the reason is
Because autounboxing converts

case int1:



into

case int1.intValue():



which is not a compile-time constant.

http://java.sun.com/docs/books/jls/third_edition/html/conversions.html#5.1.8

also, one more thing
The reason it is not allowed is ,we can assign a null value (it is not necessary to assign a int value when we declare final variable) to the integer wrapper class and in such a case it will throw NumberFormatException if used in the case statement.

So it is designed in such a way to avoid this problem by not allowing wrapper class in case statement.