How to Get a List from a Stream in Java

Published Jan 19, 2022  ∙  Updated May 2, 2022

Suppose we have list of integers called src that we want to convert to a stream and filter.

src.stream().filter(num -> num > 2)

Let’s say we want to store the result in this dst list.

List<Integer> dst;

Get list from stream with Collectors.toList()

We can use Collectors.toList() to retrieve a list from a stream.

dst = src.stream()
         .filter(num -> num > 2)
         .collect(Collectors.toList());

The only issue with Collectors.toList() can be seen in the Java documentation on Collectors:

There are no guarantees on the type, mutability, serializability, or thread-safety of the List returned; if more control over the returned List is required, use toCollection(Supplier).

Get list from stream with Collectors.toCollection()

If we want a particular List implementation (i.e. ArrayList, LinkedList, etc.), then we can use Collectors.toCollection().

dst = src.stream()
         .filter(num -> num > 2)
         .collect(Collectors.toCollection(ArrayList::new));