why public static final string can not used in java switch

Question

java support switch a string, but in the case field, how to use a constant string? Like this:

PhxLog l = new PhxLog();        
for (String s : l.FIELDS) {
        Object v = mapBaseData.getData().get(s);
            switch (s) {
                case l.LOG_FIELD_TIME:   // this is wrong, but how to use a constant instead of a "xxxx"
                    l.setTime((String)v);
                    break;

Answer 1

(Credit goes to EJP's answer)

From JLS , it mentioned that expression you put in case needs to be a Constant Expression.

There are different form of Constant Expression, and String contants are in the list:

Qualified names (§6.5.6.2) of the form TypeName . Identifier that refer to constant variables (§4.12.4).

From your code, it gives a hint that l.LOG_FIELD_TIME does not fulfill the requirement, because l is not a TypeName (hinted by for (String s : l) { ). If LOG_FIELD_TIME is really a static final field, you should use ClassNameOfL.LOG_FIELD_TIME instead, and thing should work.

Answer 2

how to use a constant instead of a "xxxx"

You can't. JLS 14.11 :

Every case label has a case constant, which is either a constant expression or the name of an enum constant.

The name of a static final String is not a constant expression.

You could use an enum , as it says.