Increment all values in a Map by 1
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&lt;String&gt;, which will make your intention clearer.

Using lambdas, your code would look like:

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


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