Roman Vinokurov :
I'm trying to replace the common switch for arithmetical operations by BinaryOperator functional interface.
The base 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 I understand it's nesessary to write something like:
BinaryOperator<Integer> action = (a,b) -> computeExpression(a + operation + b);
action.apply(res, operand);
But I don't understand how to avoid switch in computeExpression that would be the same as computeOne.
Andrew Tobilko :
You can define a 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 one passing 2 arguments:
// result = operation.apply(a, b);
int result = ((BinaryOperator<Integer>) ((a, b) -> a * b)).apply(2, 2);
I would use an enum to enumerate these operations:
class Test {
public static void main(String[] args) {
System.out.println(computeOne(4, "2", "/")); // 2
System.out.println(computeOne(4, "2", "*")); // 8
System.out.println(computeOne(4, "2", "-")); // 2
System.out.println(computeOne(4, "2", "+")); // 6
}
private static int computeOne(int res, String operand, String operation) {
return Operation.getOperationBySymbol(operation)
.getBinaryOperator()
.apply(res, Integer.parseInt(operand));
}
private enum Operation {
// operation = symbol, action
MULTIPLICATION("*", (a, b) -> a * b),
ADDITION("+", (a, b) -> a + b),
SUBTRACTION("-", (a, b) -> a - b),
DIVISION("/", (a, 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 also can "simplify" it with a BiFunction<BinaryOperator<?>, Pair<?, ?>, ?>:
// 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
Guess you like
Origin http://10.200.1.11:23101/article/api/json?id=443245&siteId=1