Best way to iterate over HashSet in Java

Question

I'm used to programming in PHP and now I'm studing Java, and the whole Collections API is a whole new thing for me.

I searched and got to know some ways to iterate over a HashSet, like using:

Java 8 forEach and lambda expression.
iterator().
iterator() and Java 8 forEachRemaining() method.
simple for-each loop.

Source and many others easily found in the internet.

But what's the best way to iterate over it or what's the difference between those, like which one should I use in different scenarios.

In the end iterator() and hasNext() and next() on it is called anyways. Just use whatever fits to the content of your loop the best. — Meini
– Meini, Commented Nov 16, 2018 at 13:56
Just stick with a for-each loop. It’s the easiest to work with (especially for beginners), and the other approaches are unlikely to provide any significant benefit in most cases. — VGR
– VGR, Commented Nov 16, 2018 at 14:12

László Stahorszki · Accepted Answer · 2018-11-16 14:17:20Z

Each has its own benefits and drawbacks. Using the iterator() and Java 8 forEachRemaining() method is not really different from the simple forEach() on the Set itself, but requires one more method to be called.

Using forEach() on the Set with lambda expressions is great, if you want one simple method call on every piece in the set.

the for(T item: someSet) {} is cleaner if you do a lot of things for each piece, or if there are side-effects to the things you do with them.

if there are no side-effects, but let's say you want to search for a specific property or a set of specific properties in the set, I'd suggest using the Stream API, where you can filter(), map(), find, or collect to some other type of collection.

Whatever you use is mainly down to what appeals to you personally. The different ways may be really different in implementation, but they can most of the times do the same things. It mainly comes down to taste or standards in the team

Nick · Accepted Answer · 2018-11-16 14:13:11Z

If you place lots of objects into Collection and want to iterate though it you should consider using List interface instead because Big-O for iteration is faster for Lists in this situation. Talking about HashSet, it merely depends on your code style and tasks you want to perform on the elements in the HashSet

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