Here’s a great look at what Java 8 brought to ConcurrentHashMaps, including close looks at the methods at your disposal and their performance impacts.

Whilst doing some refactoring on updates to ConcurrentHashMap values, I came across these great articles …

• https://dzone.com/articles/concurrenthashmap-isnt-always-enough?fromrel=true
• https://dzone.com/articles/how-concurrenthashmap-works-internally-in-java?fromrel=true

… and was inspired to try to develop the theme a bit further.

Pre-Java 8, we had various ways to try to perform atomic operations on the values of Concurrent collections as described by Dima.

For example, a simple counter:

Java

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// Incrementing a count of the occurrences of a currency symbol

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// (In reality we would have used an atomic variable even pre Java 8)

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ConcurrentHashMap <String Integer> map = new ConcurrentHashMap <>();

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String key = "USD/JPY";

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Double oldValue; Double newValue; double increment = 1.0;

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do {

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    oldValue = results.get(key);

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    newValue = oldValue == null? increment: oldValue + increment;

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} while (!results.replace(key, oldValue, newValue));

#java #tutorial #java 8 #java performance #concurrenthashmap #atomic updates