Converting an Iterator to a Stream Without Copying

When working with data structures, the need often arises to manipulate and process data in different ways. One common scenario is the conversion of an Iterator, a sequential collection of elements, into a Stream, a more versatile and powerful data processing pipeline.

To achieve this conversion effectively, it's essential to avoid creating copies of the data. This is both inefficient and unnecessary, especially when dealing with large datasets.

One approach is to utilize the StreamSupport class. It provides methods to create a stream from an Iterable or Spliterator. In this case, we can create a Spliterator from the Iterator using Spliterators.spliteratorUnknownSize(). Here's an example:

Iterator sourceIterator = Arrays.asList("A", "B", "C").iterator();
Stream targetStream = StreamSupport.stream(
    Spliterators.spliteratorUnknownSize(sourceIterator, Spliterator.ORDERED),
    false);

Another option involves creating an Iterable from the Iterator. Iterable is a functional interface, and with lambdas, we can easily create an Iterable from an Iterator:

Iterable iterable = () -> sourceIterator;
Stream targetStream = StreamSupport.stream(iterable.spliterator(), false);

This approach is arguably more readable, as it utilizes the functional interface design. By avoiding unnecessary copying, you can efficiently process your data while maintaining performance and code clarity.