In Java, when working with filter, map, etc. you need to call the stream() method. Why and why is it designed this way?

Question

Java

Hello everyone,
I'm not a Java developer but I'm interested in this question.
As I understand it, the Java Stream API is just a really cool bunch of syntactic sugar and functionality.
Most languages ​​such as Ruby, C#, and others do well without this method. If we need to filter the collection, we simply apply the filter without streams, and this is convenient and understandable.
I'm wondering why the designers of Java added the stream() method?
From my side it looks like a crutch.

Answer 1

В Java нет методов расширения, потому на коллекцию можно "навешивать" функциональность аналогичным образом (C#/LINQ), оборачивая коллекцию в Stream<T>.

Answer 2

stream is a recipe for streaming data. in order for it to do anything, a terminal operation is needed. it's done for laziness.
for example:
listOf(1,2,3,4,5).stream().filter(it -> it > 3).map(it -> it + 1)
this line will not do anything, since the stream is not closed ( no terminal operation)
listOf(1,2,3,4,5).stream().filter(it -> it > 3).map(it -> it + 1).collect(toList())
now has a terminal the collect operation and the string will work as expected.
and all this will be performed lazily (in one cycle), that is, we will not bypass the list 2 times, we will bypass it 1 time sequentially applying operations
in this case, the element is checked for> 3, increases by 1, the next number is checked for> 3. increases by 1 and so on.

Answer 3

Посмотрите, все описал, что зачем и почему. javarules.ru/stream-api