enum as arithmetic operation

Question

Suppose there is an ENUM

enum Operations { 
  ADD, 
  SUBTRACT, 
  MULTIPLY
}

I want to use this enum to add two numbers(say 5 and 3) and get the output as 8 or I want to use this enum to subtract two numbers(say 9 and 3) and get the output as 6

Question:

• is this possible?
• if yes than what are the modifications to be done to this enum?

Answer 1

enums can have abstract methods, and each member can implement it differently.

enum Operations {
  ADD {
    public double apply(double a, double b) { return a + b; }
  }, 
  SUBTRACT {
    public double apply(double a, double b) { return a - b; }
  }, 
  MULTIPLY {
    public double apply(double a, double b) { return a * b; }
  }, 
  ;

  public abstract double apply(double a, double b);
}

will allow you to do

Operations op = ...;
double result = op.apply(3, 5);

Answer 2

How about using JAVA 8 features:

enum Operation implements DoubleBinaryOperator {
    PLUS    ("+", (l, r) -> l + r),
    MINUS   ("-", (l, r) -> l - r),
    MULTIPLY("*", (l, r) -> l * r),
    DIVIDE  ("/", (l, r) -> l / r);

    private final String symbol;
    private final DoubleBinaryOperator binaryOperator;

    private Operation(final String symbol, final DoubleBinaryOperator binaryOperator) {
        this.symbol = symbol;
        this.binaryOperator = binaryOperator;
    }

    public String getSymbol() {
        return symbol;
    }

    @Override
    public double applyAsDouble(final double left, final double right) {
        return binaryOperator.applyAsDouble(left, right);
    }
}