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25 package java.lang;
26 
27 import java.util.Iterator;
28 import java.util.Objects;
29 import java.util.Spliterator;
30 import java.util.Spliterators;
31 import java.util.function.Consumer;
32 
33 /**
34  * Implementing this interface allows an object to be the target of the enhanced
35  * {@code for} statement (sometimes called the "for-each loop" statement).
36  *
37  * @param <T> the type of elements returned by the iterator
38  *
39  * @since 1.5
40  * @jls 14.14.2 The enhanced {@code for} statement
41  */
42 public interface Iterable<T> {
43     /**
44      * Returns an iterator over elements of type {@code T}.
45      *
46      * @return an Iterator.
47      */
iterator()48     Iterator<T> iterator();
49 
50     /**
51      * Performs the given action for each element of the {@code Iterable}
52      * until all elements have been processed or the action throws an
53      * exception.  Actions are performed in the order of iteration, if that
54      * order is specified.  Exceptions thrown by the action are relayed to the
55      * caller.
56      * <p>
57      * The behavior of this method is unspecified if the action performs
58      * side-effects that modify the underlying source of elements, unless an
59      * overriding class has specified a concurrent modification policy.
60      *
61      * @implSpec
62      * <p>The default implementation behaves as if:
63      * <pre>{@code
64      *     for (T t : this)
65      *         action.accept(t);
66      * }</pre>
67      *
68      * @param action The action to be performed for each element
69      * @throws NullPointerException if the specified action is null
70      * @since 1.8
71      */
forEach(Consumer<? super T> action)72     default void forEach(Consumer<? super T> action) {
73         Objects.requireNonNull(action);
74         for (T t : this) {
75             action.accept(t);
76         }
77     }
78 
79     /**
80      * Creates a {@link Spliterator} over the elements described by this
81      * {@code Iterable}.
82      *
83      * @implSpec
84      * The default implementation creates an
85      * <em><a href="../util/Spliterator.html#binding">early-binding</a></em>
86      * spliterator from the iterable's {@code Iterator}.  The spliterator
87      * inherits the <em>fail-fast</em> properties of the iterable's iterator.
88      *
89      * @implNote
90      * The default implementation should usually be overridden.  The
91      * spliterator returned by the default implementation has poor splitting
92      * capabilities, is unsized, and does not report any spliterator
93      * characteristics. Implementing classes can nearly always provide a
94      * better implementation.
95      *
96      * @return a {@code Spliterator} over the elements described by this
97      * {@code Iterable}.
98      * @since 1.8
99      */
spliterator()100     default Spliterator<T> spliterator() {
101         return Spliterators.spliteratorUnknownSize(iterator(), 0);
102     }
103 }
104