Simple Java 8 Stream API performance test

Simple Java 8 Stream API performance test

  // Test whether Stream API operations are efficiently re-ordered.
  // LOGGER is instance of org.slf4j.Logger
  @Test
  public void testStreamApiOrdering() {
    final Random rnd = new Random();
    final int nItems = 10_000;
    final List<Integer> values = new ArrayList<>(nItems);
    for (int i = 0; i < nItems; ++i) {
      values.add(rnd.nextInt(1000)); // Values between 0 and 999, inclusive.
    }

    // Limit argument for filtering operation, should cut down the number of elements to ~1% of original.
    final int limit = 10;

    // No delay: Baseline.
    long start = System.currentTimeMillis();
    long filteredCount = values.stream().filter(i -> i < limit).map(StreamApiTest::identity).count();
    LOGGER.debug("Baseline: Objects filtered and identity-mapped: {}; Time taken: {} ms.", filteredCount, System.currentTimeMillis() - start);

    // Filtering and then expensive operation.
    start = System.currentTimeMillis();
    filteredCount = values.stream().filter(i -> i < limit).map(StreamApiTest::expensiveOperation).count();
    LOGGER.debug("Variation #1: Objects filtered and then expensively-mapped: {}; Time taken: {} ms.", filteredCount, System.currentTimeMillis() - start);

    // Expensive operation and then filtering.
    start = System.currentTimeMillis();
    filteredCount = values.stream().map(StreamApiTest::expensiveOperation).filter(i -> i < limit).count();
    LOGGER.debug("Variation #2: Objects expensively-mapped and then filtered: {}; Time taken: {} ms.", filteredCount, System.currentTimeMillis() - start);
  }

  public static Integer expensiveOperation(final Integer input) {
    try {
      Thread.sleep(1L);
    } catch (final InterruptedException e) {
      // Do nothing, just testing...
    }
    return identity(input);
  }

  public static Integer identity(final Integer input) {
    return input;
  }