问题:

Consider Below 2 examples.

1 With Streams

myList.stream().map(this::getInt).max(Integer::compareTo);

2 Old way

int max = Integer.MIN_VALUE;
for (MyItem item : myList) {
    max = Math.max(max, getInt(item));    
}

Above getInt method accepts a MyItem argument and returns an int result.

Here, #2 gives me a much lower latency compared to #1. Does anyone have an idea why or anything going wrong for me?

回答1:

myList.stream().mapToInt(this::getInt).max()

Try mapping to an IntStream. An IntStream works with ints internally, which avoids the overhead of boxing and unboxing Integer objects. Also, IntStream.max() doesn't need a custom comparator.

So you suggest that the prominent reason is 'boxing' and 'unboxing'?

Without running it through your benchmark I don't know if it'll match the for loop's performance. But it'll be an improvement. If it's not good enough then I suggest sticking with the loop as I don't see any other way to improve it.

回答2:

You should probably take advantage of features of Streams, that should optimise these cases. Read the docs for Streams, the first example shows the optimised path for IntStream.

https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html

     int max = myList.stream()
                      .mapToInt(this::getInt)
                      .max()
                      .orElse(Integer.MIN_VALUE);