Using Stream methods in current stream method in Java 8

Question

I got a group of Integers and I want to count the amount of max() integers my stream contains. The max() method is from within the Stream API.

I was going for something like this

int count = Arrays.stream(myIntArray)
            .filter(i -> i == max())
            .count();
System.out.printf("Count: %d", count);

I can't call the max() method from within my forEach() method since that's not how Streams function – so what can I do to make this work?

Answer 1

You can't do anything like this, not without a lot of hassle. The simplest way of writing what you want would be two stages:

int max = Arrays.stream(array).max().getAsInt();
int count = (int) Arrays.stream(array).filter(i -> i == max).count();

If you insist on doing it in one pass, I'd write something like

int[] maxAndCount = Arrays.stream(array).collect(
    () -> new int[2], // first max, then count
    (maxAndCount, i) -> {
      if (i > maxAndCount[0] || maxAndCount[1] == 0) {
        maxAndCount[0] = i;
        maxAndCount[1] = 1;
      } else if (i == maxAndCount[0]) {
        maxAndCount[1]++;
      }
    },
    (maxAndCount1, maxAndCount2) -> {
      if (maxAndCount1[0] < maxAndCount2[0]) {
        maxAndCount1[0] = maxAndCount2[0];
        maxAndCount1[1] = maxAndCount2[1];
      } else if (maxAndCount1[0] == maxAndCount2[0]) {
        maxAndCount1[1] += maxAndCount2[1];
      }
    });
  int count = maxAndCount[1];

...but honestly, the simple two-stage version is hard to beat. (And frankly I'd expect it to perform better.)