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package java.lang;

import java.util.Iterator;
import java.util.Objects;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.Consumer;


Implementing this interface allows an object to be the target of the enhanced for statement (sometimes called the "for-each loop" statement). 
Type parameters:
  • <T> – the type of elements returned by the iterator
Since:1.5
@jls14.14.2 The enhanced for statement
/**
 * Implementing this interface allows an object to be the target of the enhanced
 * {@code for} statement (sometimes called the "for-each loop" statement).
 *
 * @param <T> the type of elements returned by the iterator
 *
 * @since 1.5
 * @jls 14.14.2 The enhanced {@code for} statement
 */
public interface Iterable<T> {
    
Returns an iterator over elements of type T. 
Returns:an Iterator.
/**
     * Returns an iterator over elements of type {@code T}.
     *
     * @return an Iterator.
     */
    Iterator<T> iterator();

    
Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception. Actions are performed in the order of iteration, if that order is specified. Exceptions thrown by the action are relayed to the caller. 

The behavior of this method is unspecified if the action performs
side-effects that modify the underlying source of elements, unless an
overriding class has specified a concurrent modification policy.

Params:
  • action – The action to be performed for each element
Throws:
Implementation Requirements:

The default implementation behaves as if:


    for (T t : this)
        action.accept(t);

Since:1.8
/**
     * Performs the given action for each element of the {@code Iterable}
     * until all elements have been processed or the action throws an
     * exception.  Actions are performed in the order of iteration, if that
     * order is specified.  Exceptions thrown by the action are relayed to the
     * caller.
     * <p>
     * The behavior of this method is unspecified if the action performs
     * side-effects that modify the underlying source of elements, unless an
     * overriding class has specified a concurrent modification policy.
     *
     * @implSpec
     * <p>The default implementation behaves as if:
     * <pre>{@code
     *     for (T t : this)
     *         action.accept(t);
     * }</pre>
     *
     * @param action The action to be performed for each element
     * @throws NullPointerException if the specified action is null
     * @since 1.8
     */
    default void forEach(Consumer<? super T> action) {
        Objects.requireNonNull(action);
        for (T t : this) {
            action.accept(t);
        }
    }

    
Creates a Spliterator over the elements described by this Iterable. 
Implementation Requirements:
The default implementation creates an
early-binding spliterator from the iterable's Iterator. The spliterator inherits the fail-fast properties of the iterable's iterator.
Implementation Note:
The default implementation should usually be overridden.  The
spliterator returned by the default implementation has poor splitting
capabilities, is unsized, and does not report any spliterator
characteristics. Implementing classes can nearly always provide a
better implementation.
Returns:a Spliterator over the elements described by this Iterable.
Since:1.8
/**
     * Creates a {@link Spliterator} over the elements described by this
     * {@code Iterable}.
     *
     * @implSpec
     * The default implementation creates an
     * <em><a href="../util/Spliterator.html#binding">early-binding</a></em>
     * spliterator from the iterable's {@code Iterator}.  The spliterator
     * inherits the <em>fail-fast</em> properties of the iterable's iterator.
     *
     * @implNote
     * The default implementation should usually be overridden.  The
     * spliterator returned by the default implementation has poor splitting
     * capabilities, is unsized, and does not report any spliterator
     * characteristics. Implementing classes can nearly always provide a
     * better implementation.
     *
     * @return a {@code Spliterator} over the elements described by this
     * {@code Iterable}.
     * @since 1.8
     */
    default Spliterator<T> spliterator() {
        return Spliterators.spliteratorUnknownSize(iterator(), 0);
    }
}