What is the default implementation of .stream() in java 8?

Question

It just says:

Returns a sequential Stream with this collection as its source.

This method should be overridden when the spliterator() method cannot return a spliterator that is IMMUTABLE, CONCURRENT, or late-binding. (See spliterator() for details.)

But I can't find any code showing how it creates and returns the new Stream.

double average = roster
.stream()
.filter(p -> p.getGender() == Person.Sex.MALE)
.mapToInt(Person::getAge)`enter code here`
.average()
.getAsDouble();

roster is a List<Person> instance of ArrayList<Person>
Person is a simple class that represents a person

Look at the source code of whatever type `roster` is and go up its object hierarchy until you find a `stream` method. — Sotirios Delimanolis, Jun 13 '14 at 00:47
i did it but nothing shows up. This is the site where i was looking for - docs.oracle.com. — user3727894, Jun 13 '14 at 00:50
`stream()` is an instance method. If it doesn't exist in `ArrayList`, it must exist in one of its supertypes. Did you look at all of its supertypes? — Sotirios Delimanolis, Jun 13 '14 at 00:57
yes, from ArrayList<> to its supertype AbstractCollection<>, and the latest is the first class that implements the Collection<> interface — user3727894, Jun 13 '14 at 01:04
The default implementation of `stream` is in `Collection`, so I don't know what source code you are looking at. — Sotirios Delimanolis, Jun 13 '14 at 01:05
[here](http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/8-b132/java/util/Collection.java#Collection.stream%28%29) — Sotirios Delimanolis, Jun 13 '14 at 01:13
man you are graet. But i should ask, is that an official site? — user3727894, Jun 13 '14 at 01:19
No, it isn't. You can find official source code on Oracle's site. It's also available in your JDK installation inside `src.zip`. — Sotirios Delimanolis, Jun 13 '14 at 01:21
any way thanks for your help, now i can see the light at the end of my way jajaja. See you. — user3727894, Jun 13 '14 at 01:24
Euh, I meant the JDK, so [here](http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html). — Sotirios Delimanolis, Jun 13 '14 at 01:29
what is the meaning of Euh, i guess you realize i'm not a native speaker, so just for learning. — user3727894, Jun 13 '14 at 01:40
No lol, "Euh", as in I was correcting myself. The JDK contains the source code. — Sotirios Delimanolis, Jun 13 '14 at 01:41

score 2 · Answer 1 · answered Jun 13 '14 at 10:18

2

Basically the whole stream implementation is package private so you won't get anything showing up at docs.oracle.com.

But take a look a look at the source code here: http://hg.openjdk.java.net/jdk8/jdk8/jdk/file/687fd7c7986d/src/share/classes/java/util/stream

You can start with StreamSupport which most classes uses to create the various streams.

answered Jun 13 '14 at 10:18

KasperNielsen

51
1
2

2

There exists only one (abstract) j.u.stream.Stream implementation: j.u.stream.ReferencePipeline which gets further specialized into ReferencePipeline.Head for the source stage of a pipeline and ReferencePipeline.StatefulOp / ReferencePipeline.StatelessOp for stateful / stateless intermediate stages of a pipeline. The same for j.u.stream.Double/Int/LongStream => j.u.stream.Double/Int/LongPipeline with corresponding Head, StatefulOp and StatelessOp static nested classes. – Stefan Zobel May 24 '15 at 14:54

What is the default implementation of .stream() in java 8?

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