带有嵌套HashMap的Java并行流

Question

Given the nested HashMap HashMap<Integer,HashMap<Integer,BigDecimal>> is it possible to set to zero inner HashMap values with parallel streams with acceptable side-effects and respecting non-interference rules?

For example,given HashMap:

HashMap<Integer,HashMap<Integer,BigDecimal>> myMap = null;

is the final forEach in:

myMap.entrySet().parallelStream().forEach(e -> {
            e.getValue().entrySet().parallelStream().forEach(e1 -> {
                e1.setValue(new BigDecimal(0));
                });
        });

acceptable side-effects and respecting non-interference rules?

Answer 1

... is it possible to set to zero inner HashMap values with parallel streams...

It seems it works, however HashMap is not the thread-safe implementation so I discourage you from using this way.

... with acceptable side-effects and respecting non-interference rules?

Your usage of Stream::for has side-effects since it changes the source of the Stream. I recommend you to use Stream::map and collecting the structure back to Map afterward using one parrallelStream :

Map<Integer, Map<Integer,BigDecimal>> myMap2 = myMap.entrySet().parallelStream()
    .map(e -> new AbstractMap.SimpleEntry<>(
        e.getKey(), 
        e.getValue().entrySet().stream()
                               .collect(Collectors.toMap(Entry::getKey, i -> BigDecimal.ZERO))))
    .collect(Collectors.toMap(Entry::getKey, Entry::getValue));