why immutable wrapper objects are not considered as compile time constant?

[Karthikeyan Kandasamy]

While going through rules for Case expressions in K&B book, its mentioned that only integer literal values and compile time constants are allowed.

I couldn't figure out why integer wrappers are not allowed in Case expressions. In the below example, variable i2 is final and it refers to Integer wrapper object (immutable). So compiler could easily use the value (200) instead of object.

class SwitchWithWrappers
{
	public static void main(String s[])
	{
	
		final int i = 200;
		final Integer i2 = 200;
		int i3=200;
		
		switch(i3) {		
			case i:
				System.out.println("got primitive - "+i);
				break;
					
			case i2:/*	Compile error:	SwitchWithWrappers.java:20: constant expression required
												case i2:
					*/
				System.out.println("got wrapper - "+i2);
				break;
			
			default:
				System.out.println("default");				
		}
	}
}

Thanks

[Enkita mody]

Compiler does compile time stuff.See more.

[Seetharaman Venkatasamy]

interesting infact!

[Matthew Brown]

Karthikeyan Kandasamy wrote:I couldn't figure out why integer wrappers are not allowed in Case expressions.

They could have been, but the language designers never bothered. You'd have to ask them for the real reason. My speculation, though - they never found a good reason to. Can you think of a situation where it would be genuinely useful?

[Seetharaman Venkatasamy]

so *I am not sure*, but i say in bottom layer compiler is runtime .

[Matthew Brown]

Seetharaman Venkatasamy wrote:so *I am not sure*, but i say in bottom layer compiler is runtime .

Sorry, but what do you mean? "compiler is runtime" doesn't make any sense to me.

[Seetharaman Venkatasamy]

Matthew Brown wrote:Sorry, but what do you mean? "compiler is runtime" doesn't make any sense to me.

s
Um. I mean javac call java .. but you are right though..

[Karthikeyan Kandasamy]

Thanks for tour responses.

@Matthew Brown, I don't have any real life requirement to use wrapper as case expression.

Thanks.

[Seetharaman Venkatasamy]

I am extremely sorry for my previous post mess .

From JLS:

Every case constant expression associated with a switch statement must be assignable (§5.2) to the type of the switch Expression.