Iterable 인터페이스와 Iterator 인터페이스

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package java.lang;

public interface Iterable<T> {
    /**
     * Returns an iterator over elements of type {@code T}.
     *
     * @return an Iterator.
     */
    Iterator<T> iterator();

    /**
     * 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);
        }
    }
}

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package java.util;

public interface Iterator<E> {
    /**
     * Returns {@code true} if the iteration has more elements.
     * (In other words, returns {@code true} if {@link #next} would
     * return an element rather than throwing an exception.)
     *
     * @return {@code true} if the iteration has more elements
     */
    boolean hasNext();

    /**
     * Returns the next element in the iteration.
     *
     * @return the next element in the iteration
     * @throws NoSuchElementException if the iteration has no more elements
     */
    E next();

    /**
     * Removes from the underlying collection the last element returned
     * by this iterator (optional operation).  This method can be called
     * only once per call to {@link #next}.
     * <p>
     * The behavior of an iterator is unspecified if the underlying collection
     * is modified while the iteration is in progress in any way other than by
     * calling this method, unless an overriding class has specified a
     * concurrent modification policy.
     * <p>
     * The behavior of an iterator is unspecified if this method is called
     * after a call to the {@link #forEachRemaining forEachRemaining} method.
     *
     * @implSpec
     * The default implementation throws an instance of
     * {@link UnsupportedOperationException} and performs no other action.
     *
     * @throws UnsupportedOperationException if the {@code remove}
     *         operation is not supported by this iterator
     *
     * @throws IllegalStateException if the {@code next} method has not
     *         yet been called, or the {@code remove} method has already
     *         been called after the last call to the {@code next}
     *         method
     */
    default void remove() {
        throw new UnsupportedOperationException("remove");
    }
}

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import java.util.Iterator;
import java.util.LinkedList;
 
public class Test {
    public static void main(String[] args) {
        LinkedList<String> list = new LinkedList<>();
        list.add("Lee"); list.add("ekk"); list.add("eww");
        Iterator it = list.iterator();
 
        while (it.hasNext()) {
            System.out.print(it.next() + " ");
        }
 
    }
}