在Java中扩展枚举

enum Color implements Printable {
    RED {
        @Override
        public void print() {
            System.out.println("This is red color.");
        }
    },
    BLUE {
        @Override
        public void print() {
            System.out.println("This is blue color.");
        }
    },
    GREEN {
        @Override
        public void print() {
            System.out.println("This is green color.");
        }
    };

    interface Printable {
        void print();
    }
}

enum Operation {
    ADD {
        @Override
        public int calculate(int a, int b) {
            return a + b;
        }
    },
    SUBTRACT {
        @Override
        public int calculate(int a, int b) {
            return a - b;
        }
    },
    MULTIPLY {
        @Override
        public int calculate(int a, int b) {
            return a * b;
        }
    },
    DIVIDE {
        @Override
        public int calculate(int a, int b) {
            return a / b;
        }
    };

    public abstract int calculate(int a, int b);
}