java - Why does Iterable<T> not provide stream() and parallelStream() methods? -

i wondering why iterable interface not provide stream() , parallelstream() methods. consider following class:

public class hand implements iterable<card> {     private final list<card> list = new arraylist<>();     private final int capacity;      //...      @override     public iterator<card> iterator() {         return list.iterator();     } } 

it implementation of hand can have cards in hand while playing trading card game.

essentially wraps list<card>, ensures maximum capacity , offers other useful features. better implementing directly list<card>.

now, convienience thought nice implement iterable<card>, such can use enhanced for-loops if want loop on it. (my hand class provides get(int index) method, hence iterable<card> justified in opinion.)

the iterable interface provides following (left out javadoc):

public interface iterable<t> {     iterator<t> iterator();      default void foreach(consumer<? super t> action) {         objects.requirenonnull(action);         (t t : this) {             action.accept(t);         }     }      default spliterator<t> spliterator() {         return spliterators.spliteratorunknownsize(iterator(), 0);     } } 

now can obtain stream with:

stream<hand> stream = streamsupport.stream(hand.spliterator(), false); 

so onto real question:

• why iterable<t> not provide default methods implement stream() , parallelstream(), see nothing make impossible or unwanted?

a related question found following though: why stream<t> not implement iterable<t>?
oddly enough suggesting other way around.

this not omission; there detailed discussion on eg list in june of 2013.

the definitive discussion of expert group rooted @ this thread.

while seemed "obvious" (even expert group, initially) stream() seemed make sense on iterable, fact iterable general became problem, because obvious signature:

stream<t> stream() 

was not going want. things iterable<integer> rather have stream method return intstream, example. putting stream() method high in hierarchy make impossible. instead, made easy make stream iterable, providing spliterator() method. implementation of stream() in collection just:

default stream<e> stream() {     return streamsupport.stream(spliterator(), false); } 

any client can stream want iterable with:

stream s = streamsupport.stream(iter.spliterator(), false); 

in end concluded adding stream() iterable mistake.