Lambda: BinaryOperator is a BiFunction whose result matches both input types

BinaryOperator<T> specializes BiFunction<T, T, T> for combining two values of the same type into one of that type, the exact shape needed for a manual running-reduction.

Code

BinaryOperator<Integer> max = (a, b) -> a > b ? a : b;
int result = 3;
for (int n : new int[]{7, 2, 9, 4}) {
    result = max.apply(result, n);
}
System.out.println("Max via BinaryOperator: " + result);

Output

Max via BinaryOperator: 9