What is the increment value in hashmap java?

1.6K    Asked by AndrewJenkins in Java , Asked on Oct 12, 2022

What's the neatest way to increment all values in a HashMap by 1? The map is , but the key doesn't matter as every value will be incremented.

Is it "cleaner" to use lambdas with forEach/compute/etc. or just loop through the entries?

HashMap map = mobCounter.get(mob);
for (Entry e : map.entrySet()) {
    map.put(e.getKey(), e.getValue() + 1);

This doesn't look too messy to me but I'm wondering if people like seeing lambdas more.

Answered by Andrew Jenkins

For the increment value in hashmap java, you must not modify the keys of a HashMap while iterating over it. You are just lucky it worked.

  Instead of the put(...), write e.setValue(e.getValue() + 1).

If you have some kind of Multiset available (e.g. when you are using Guava), you could replace your HashMap with a Multiset, which will make your intention clearer. Using lambdas, your code would look like:

  map.replaceAll((k, v) -> v + 1);

This looks very nice to me. It cannot get any shorter.

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