Lambda: a decorator wraps a Function to add logging around its logic

A decorator lambda takes an existing Function and returns a new one that runs extra behavior, such as logging, before and after delegating to the original, without changing the original function's code.

Code

static Function<Integer, Integer> withLogging(Function<Integer, Integer> original) {
    return x -> {
        System.out.println("Calling with input " + x);
        int result = original.apply(x);
        System.out.println("Result was " + result);
        return result;
    };
}
Function<Integer, Integer> square = x -> x * x;
Function<Integer, Integer> logged = withLogging(square);
logged.apply(4);

Output

Calling with input 4
Result was 16