Difference between final variables and compile time constant

Question

What is the difference between final variables and compile time constants?

Consider the following code

final int a = 5; final int b; b=6; int x=0; switch(x) {      case a: //no error      case b: //compiler error } 

What does this mean? When and how are final variables assigned a value? What happens at run time and what happens at compile time? Why should we give switch a compile time constant? What other structures of java demands a compile time constant?

Answer 1

The problem is, that all case: statements must be ultimate at compile time. Your first statement is ultimate. a will for 100% be no other value than 5.

final int a = 5; 

However, this is not guaranteed for b. What if there would be an if-statement around b?

final int b; if(something())    b=6; else    b=5;