[java] Switch on Enum in Java

Why can't you switch on an enum in Java? It seems simple enough to do and would make for some convenient code. Also this question could apply to String's. You can switch on a char, but not a String ...?

You definitely can switch on enums. An example posted from the Java tutorials.

public enum Day {
    SUNDAY, MONDAY, TUESDAY, WEDNESDAY, 
    THURSDAY, FRIDAY, SATURDAY 
}

public class EnumTest {
    Day day;

    public EnumTest(Day day) {
        this.day = day;
    }

    public void tellItLikeItIs() {

        switch (day) {
            case MONDAY: 
                System.out.println("Mondays are bad.");
                break;

            case FRIDAY: 
                System.out.println("Fridays are better.");
                break;

            case SATURDAY:
            case SUNDAY: 
                System.out.println("Weekends are best.");
                break;

            default:
                System.out.println("Midweek days are so-so.");
                break;
        }
    }
}

First, you can switch on an enum in Java. I'm guessing you intended to say you can’t, but you can. chars have a set range of values, so it's easy to compare. Strings can be anything.

A switch statement is usually implemented as a jump table (branch table) in the underlying compilation, which is only possible with a finite set of values. C# can switch on strings, but it causes a performance decrease because a jump table cannot be used.

Java 7 and later supports String switches with the same characteristics.

Actually you can use a switch statement with Strings in Java...unfortunately this is a new feature of Java 7, and most people are not using Java 7 yet because it's so new.

Article on Programming.Guide: Switch on enum

enum MyEnum { CONST_ONE, CONST_TWO }

class Test {
        public static void main(String[] args) {
            MyEnum e = MyEnum.CONST_ONE;

            switch (e) {
                case CONST_ONE: System.out.println(1); break;
                case CONST_TWO: System.out.println(2); break;
            }
        }
    }

Switches for strings are implemented in Java 7.

You actually can switch on enums, but you can't switch on Strings until Java 7. You might consider using polymorphic method dispatch with Java enums rather than an explicit switch. Note that enums are objects in Java, not just symbols for ints like they are in C/C++. You can have a method on an enum type, then instead of writing a switch, just call the method - one line of code: done!

enum MyEnum {
    SOME_ENUM_CONSTANT {
        @Override
        public void method() {
            System.out.println("first enum constant behavior!");
        }
    },
    ANOTHER_ENUM_CONSTANT {
        @Override
        public void method() {
            System.out.println("second enum constant behavior!");
        }
    }; // note the semi-colon after the final constant, not just a comma!
    public abstract void method(); // could also be in an interface that MyEnum implements
}

void aMethodSomewhere(final MyEnum e) {
    doSomeStuff();
    e.method(); // here is where the switch would be, now it's one line of code!
    doSomeOtherStuff();
}

You might be using the enums incorrectly in the switch cases. In comparison with the above example by CoolBeans.. you might be doing the following:

switch(day) {
    case Day.MONDAY:
        // Something..
        break;
    case Day.FRIDAY:
        // Something friday
        break;
}

Make sure that you use the actual enum values instead of EnumType.EnumValue

Eclipse points out this mistake though..