How to iterate x times using Java 8 stream? [duplicate]

Question

I have an old style for loop to do some load tests:

For (int i = 0 ; i < 1000 ; ++i) {
  if (i+1 % 100 == 0) {
    System.out.println("Test number "+i+" started.");
  }
  // The test itself...
}

How can I use new Java 8 stream API to be able to do this without the for?

Also, the use of the stream would make it easy to switch to parallel stream. How to switch to parallel stream?

* I'd like to keep the reference to i.

Answer 1

IntStream.range(0, 1000)
         /* .parallel() */
         .filter(i -> i+1 % 100 == 0)
         .peek(i -> System.out.println("Test number " + i + " started."))
         /* other operations on the stream including a terminal one */;

If the test is running on each iteration regardless of the condition (take the filter out):

IntStream.range(0, 1000)
         .peek(i -> {
             if (i + 1 % 100 == 0) {
                 System.out.println("Test number " + i + " started.");
             }
         }).forEach(i -> {/* the test */});

Another approach (if you want to iterate over an index with a predefined step, as @Tunaki mentioned) is:

IntStream.iterate(0, i -> i + 100)
         .limit(1000 / 100)
         .forEach(i -> { /* the test */ });

---

There is an awesome overloaded method Stream.iterate(seed, condition, unaryOperator) in JDK 9 which perfectly fits your situation and is designed to make a stream finite and might replace a plain for:

Stream<Integer> stream = Stream.iterate(0, i -> i < 1000, i -> i + 100);