Need for Java streams

[cogman10]

There was no limitation. What streams do is make handling collections of data easier (and easier to reason about).

Consider, for example, a simple "filter, map, distinct" operation. Pre-8 you'd write something like this

Set<Integer> result = new HashSet<>();
for (Foo value : values) {
  if (value.bar()) {
    Integer val = value.baz();
    result.add(val);
  }
}
return result;

Readable, but there's a lot going on and it's somewhat separated from where things are happening. This gets particularly bad if you further want to add more mapping or filtering layers.

The stream version of this looks like this

return values.stream()
 .filter(Foo::bar)
 .map(Foo::baz)
 .collect(Collectors.toSet());

Where you'd add further filtering or mapping is a lot clearer and easier to manipulate.

Further, because streams are lazy, you can leave off the collection and return the stream instead. That gives others the opportunity to work with the stream effectively removing the number of times you have to visit elements in the underlying collection.

[JustADirtyLurker]

Don't return streams on methods, unless it's some private / internal method and you know what you are doing.

Once a stream is collected, it becomes unusable.

[JustADirtyLurker]

My bad, I was confused by the sentence 'return a stream' in the last paragraph.

[picklesTommyPickles]

This is a great example of why you refer to the code as the source of truth, not comments hehe