Switch statement

[kish kumar]

final int a =1;
final int b;
b=2;
int x=0;
switch(x){

case a :
case b:
}

this code gave compile time error. The rule says a and b must be compile time constants. a and b are assigned values 1 ,2 at compile time only.so what is the issue?
can any one explain

[champak bhumia]

b isnt a compile time constant as it is not initilaised at the same line where it was declared

[Alpesh Rathod]

You cannot have final variables as case constants .......

[Neha Daga]

Alpesh Rathod wrote:You cannot have final variables as case constants .......

Final variables are constant their value does not change, Problem is switch accepts only compile time constants.
Final variables declared and initialised on one line are compile time constants like 'a' in the example so switch will accept it.
but final variables declared on one line and initialised on some other line are not compile time constants like 'b' in the code so switch will not allow it.

topic has been discussed earlier like here or here

[kish kumar]

The gist is
"final variables are assigned values at compile time.
If final variable declared at one line and assigned value at next line, the value to final variable will be assigned at run time.
non final variables are assigned values at run time."

Correct Neha !

[Neha Daga]

yup

[kish kumar]

There is a small correction :

if ther is a reference final Integer k = 10;

even though we are initializing it at the same line it wont be a compile time constant.If i say case k in a switch statement itwill give compiler error.

[Harpreet Singh janda]

Yes you are correct, because Wrappers are also initialized at run time even if you have provided the value while declaring.

[Seetharaman Venkatasamy]

Harpreet janda wrote:Wrappers are also initialized at run time even if you have provided the value while declaring.

Exactly, for more clarification

 final Integer b = 10;   

is converted to

 final Integer b = Integer.valueOf(10);   

by the Compiler

[Ann Johnston]

So... Can I use an Integer in the switch bit, but not in the case bits?

Integer x = new Integer(3);
switch (x) {
case 1: System.out.println("value is 1"); break;
case 2: System.out.println("value is 2"); break;
case 3: System.out.println("value is 3"); break;
default: System.out.println("don't know value");break;
}

[Abimaran Kugathasan]

Ann Johnston wrote:So... Can I use an Integer in the switch bit, but not in the case bits?

Integer x = new Integer(3);
switch (x) {
case 1: System.out.println("value is 1"); break;
case 2: System.out.println("value is 2"); break;
case 3: System.out.println("value is 3"); break;
default: System.out.println("don't know value");break;
}

For switch bit, that's not a problem. We can use....

[Ankit Garg]

Ann Johnston wrote:So... Can I use an Integer in the switch bit, but not in the case bits?

Wouldn't you get an answer if you try to compile the program that you just created??