Can an enum implement an interface?

Yes, in Java, an enum can implement an interface. This allows defining a set of methods that must be implemented by each enum element, ensuring polymorphism.

Example:

interface Operation {
    double apply(double x, double y);
}

public enum BasicOperation implements Operation {
    PLUS {
        public double apply(double x, double y) { return x + y; }
    },
    MINUS {
        public double apply(double x, double y) { return x - y; }
    },
    TIMES {
        public double apply(double x, double y) { return x * y; }
    },
    DIVIDE {
        public double apply(double x, double y) { return x / y; }
    };
}

Thus, each enum element implements the interface method, allowing the enum to be used as a set of strategies or operations.