java 8 switch statement with wrapper classes

Asked Apr 06 '21 at 15:14

Active Apr 06 '21 at 15:14

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I am studying for my Java OCA exam and I am playing with switch statement. As far as I know I can use a final constant variable in a case statement but my example is not compiling because the variable I am not using apparently it is not a constant expression:

public class SwitchOca {
    public static void main(String[] args) {
        final Integer x = Integer.valueOf(0);
        final Integer y = Integer.valueOf(0);
        switch(x) {
            case y:
                System.out.println("error ...");
                break;
            case 0:
                System.out.println("primitive ...");
                break;
        }
    }
}

The output of the compilation says:

javac SwitchOca.java
Picked up _JAVA_OPTIONS: -Xmx1024M
SwitchOca.java:6: error: constant expression required
            case y:
                 ^
1 error

Any help to understand this will be much appreciated.

asked Apr 06 '21 at 15:14

Francesco Dassisis

3

That's an `Integer` which is not a [constant expression](https://docs.oracle.com/javase/specs/jls/se11/html/jls-15.html#jls-ConstantExpression) (money quote: "a value of primitive type or a String", then more constraints) – Federico klez Culloca Apr 06 '21 at 15:17
The only reference-typed variables which can be constant expressions are Strings: and they are only constant expressions if they are initialized from string literals or concatenations of constant expressions. – Andy Turner Apr 06 '21 at 15:17
a final varibale is a constant expression sorry... – Francesco Dassisis Apr 06 '21 at 15:24
it doesn;t work for String class neither – Francesco Dassisis Apr 06 '21 at 15:29
@FrancescoDassisis please edit your question accordingly. – Federico klez Culloca Apr 06 '21 at 15:31

java 8 switch statement with wrapper classes

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