Calculator done with enums for the operation

EnumCalculator.java

public class EnumCalculator {

    //Notice how concise the code has become in the logic

    public int calculate(char op, int a, int b) {
        return OperationEnum.of(op).operate(a,b);
    }
}

OperationEnum.java

import java.util.HashMap;
import java.util.Map;
import java.util.function.BinaryOperator;

public enum OperationEnum {

    OP_PLUS         ((a,b) -> a+b),
    OP_MINUS        ((a,b) -> a-b),
    OP_TIMES        ((a,b) -> a*b),
    OP_DIVISION     ((a,b) -> a/b);

    private static Map<Character, OperationEnum> operations =
        new HashMap<Character, OperationEnum>() {{
            put('+', OP_PLUS);
            put('-', OP_MINUS);
            put('x', OP_TIMES);
            put('/', OP_DIVISION);
        }};

    private BinaryOperator<Integer> operation;

    OperationEnum(BinaryOperator<Integer> operation) {
        this.operation = operation;
    }

    public static OperationEnum of(char op) {
        if(!operations.containsKey(op)) throw new IllegalArgumentException();

        return operations.get(op);
    }

    public int operate(int a, int b) {
        return operation.apply(a,b);
    }

}