String case expressions must be constant expressions

I have the following:

public class Asd
{
    static final String VERSION = "version";
    static final String ECHO    = "echo".toUpperCase();
    public Asd()
    {
        String key = ECHO;
        switch (key)
        {
            case VERSION:
                break;

            case ECHO:
                break;
        }
    }
}

I get a compiler error that case ECHO: is not a constant expression. The designation final static defines a constant.

The constant ECHO will resolve from "echo" to "ECHO" when the class is instantiated. By the time the switch/case is evaluated, ECHO does equal "ECHO" and cannot be changed.

Or does a switch/case with String have some special background pointers to a String?

Because using

public class Asd
{
    static final int VERSION = 1;
    static final int ECHO    = 1 + 2;

    public Asd()
    {
        int key = ECHO;

        switch (key)
        {
            case VERSION:
                break;

            case ECHO:
                break;
        }
    }
}

Is error free even though 1 + 2 must be evaluated.