Java – replace switch with binaryoperator

I'm trying to replace the common switch for arithmetic operations with the binaryoperator function interface

The basic method is:

private static int computeOne(int res,String operand,String operation) {
    int number = Integer.parseInt(operand);

    switch (operation) {
        case "+":
            res += number;
            break;
        case "-":
            res -= number;
            break;
        case "*":
            res *= number;
            break;
        case "/":
            res = (number != 0 ? res / number : Integer.MAX_VALUE);
            break;
        default:
            res = 0;
            System.out.println("unkNown operation");
    }

    return res;
}

As far as I know, it is necessary to write something like this:

BinaryOperator<Integer> action = (a,b) -> computeExpression(a + operation + b);
action.apply(res,operand);

But I don't know how to avoid switching the same switch as computeone in computeexpression

Solution

You can define binaryoperator < integer > for each arithmetic operation:

// a = operand 1
// b = operand 2
(a,b) -> a * b;
(a,b) -> a + b;
(a,b) -> a / b;
(a,b) -> a - b;

Then you can apply a pass 2 parameters:

// result = operation.apply(a,b);
int result = ((BinaryOperator<Integer>) ((a,b) -> a * b)).apply(2,2);

I will use enumeration to enumerate these operations:

class Test {

    public static void main(String[] args) {
         System.out.println(computeOne(4,"2","/"));  // 2
         System.out.println(computeOne(4,"*"));  // 8
         System.out.println(computeOne(4,"-"));  // 2
         System.out.println(computeOne(4,"+"));  // 6
    }

    private static int computeOne(int res,String operation) {
        return Operation.getOperationBySymbol(operation)
                        .getBinaryOperator()
                        .apply(res,Integer.parseInt(operand));
    }

    private enum Operation {
        // operation = symbol,action
        MULTIPLICATION("*",(a,b) -> a * b),ADDITION("+",b) -> a + b),SUBTRACTION("-",b) -> a - b),DIVISION("/",b) -> a / b);

        private final BinaryOperator<Integer> binaryOperator;
        private final String symbol;

        Operation(String symbol,BinaryOperator<Integer> binaryOperator) {
            this.symbol = symbol;
            this.binaryOperator = binaryOperator;
        }

        public BinaryOperator<Integer> getBinaryOperator() {
            return binaryOperator;
        }

        public String getSymbol() {
            return symbol;
        }

        public static Operation getOperationBySymbol(String symbol) {
            for (Operation operation : values()) {
                if (operation.getSymbol().equals(symbol)) {
                    return operation;
                }
            }

            throw new IllegalArgumentException("UnkNown symbol: " + symbol);
        }
    }

}

You can also use bifunction < < binaryoperator , Pair<？,？>,？> To "simplify" it:

// BiFunction<Operator,Operands,Result>
// Operator = BinaryOperator<?>
// Operands = Pair<?,?>
BiFunction<BinaryOperator<Integer>,Pair<Integer,Integer>,Integer> f = 
    (operator,operands) -> 
        operator.apply(operands.getKey(),operands.getValue());

f.apply((a,b) -> a + b,new Pair<>(2,2)); // 4