A switch-case statement question

[Amelia Ma]

What will be the result of attempting to compile and run the following program?

   
public class KeepOnSwitching {
  public static void main(String[] args) {
    final int iLoc = 3;
    final Integer iFour = 4;
    Integer iRef = 4;
    switch (iRef) {
      case 1:
      case iLoc:
      case 2 * iLoc:
        System.out.printlin("I am ont OK.");
      default:
        System.out.printlin("You are OK.");
     case iFour:
        System.out.printlin("It's OK");
    }
  }
}

Correct answer is that the code will fail to compile. Because the value of the case label iFour is not a constant expression.
I totally don't understand. Isn't iFour is a compile time constant and become 4 through unboxing?
This problem come from "A Programmer's Guide to Java SCJP Certification", Chapter 6.2, page 215.
Thanks.

[rohan yadav]

Try this:

  public class KeepOnSwitching {
  public static void main(String[] args) {
    final int iLoc = 3;
    final int iFour = 4;
    Integer iRef = 4;
    switch (iRef) {
      case 1:
      case iLoc:
      case 2 * iLoc:
        System.out.println("I am ont OK.");
      default:
        System.out.println("You are OK.");
     case iFour:
        System.out.println("It's OK");
    }
  }
}
  

Wrapping takes place at runtime(Integer to int), and you require compile time constants for switch case.

[Rein de Boer]

To add to the previous post, iFour is a reference variable (to object type Integer), not a value type. So therefore not usable in a case.

[Amelia Ma]

Rein de Boer wrote:To add to the previous post, iFour is a reference variable (to object type Integer), not a value type. So therefore not usable in a case.

so all wrapper classes (Integer Character Short Byte) can't be in the case expression, right?

[Henry Wong]

Amelia Ma wrote:I totally don't understand. Isn't iFour is a compile time constant and become 4 through unboxing?

As a side note to this topic... compile time constants require that the type be a primative or a string. The Java Language Specification currently doesn't support any other type as a compile time constant.

Henry