This manual is for an old version of Hazelcast Jet, use the latest stable version.

We want to count how many times each word occurs in the text. If we want to do a word count without using a DAG and in a single-threaded computation, we could do it as shown below:

Pattern pattern = Pattern.compile("\\s+");
Map<String, Long> counts = new HashMap<>();
for (String line : map.values()) {
    for (String word : pattern.split(line)) {
        counts.compute(word.toLowerCase(), (w, c) -> c == null ? 1L : c + 1);

As soon as we try to parallelize this computation, it becomes clear that we have to model it differently. More complications arise on top of that when we want to scale out across multiple machines.