Java Enums can have behavior?

Question

In Java, an Enum can do the great things that Enums do, but can also have methods (behavior and logic). What advantage does that have over using a class using an enum? Simple examples to illustrate the point would also be welcome.

Answer 1

Here's a simple example:

enum RoundingMode {
    UP {
        public double round(double d) {
            return Math.ceil(d);
        }
    },
    DOWN {
        public double round(double d) {
            return Math.floor(d);
        }
    };

    public abstract double round(double d);
}

Answer 2

Enum types are also a great way to implement true singletons.

Classic singleton patterns in Java typically involve private constructors and public static factory methods but are still vulnerable to instantiation via reflection or (de-)serialization. An enum type guards against that.