How to access Java Collection through iterator

1. Description

The Collection interface has three sub-interfaces, List, Set and Queue. List will save elements in the order in which they are inserted, and elements in Set cannot be repeated. Collection defines some public methods, these basic tool methods, such as determining the size of the container, judging whether the container is empty, emptying the container, iterating the container elements, etc.

2. Example

interface Collection<E> extends Iterable<E> {
    
    int size();
    boolean isEmpty();
    boolean contains(Object o);
    Iterator<E> iterator();
    Object[] toArray();
    <T> T[] toArray(T[] a);
    default <T> T[] toArray(IntFunction<T[]> generator) {
        return toArray(generator.apply(0));
    }
    boolean add(E e);
    boolean remove(Object o);
    boolean containsAll(java.util.Collection<?> c);
    boolean addAll(java.util.Collection<? extends E> c);
    boolean removeAll(java.util.Collection<?> c);
    default boolean removeIf(Predicate<? super E> filter) {
        Objects.requireNonNull(filter);
        boolean removed = false;
        final Iterator<E> each = iterator();
        while (each.hasNext()) {
            if (filter.test(each.next())) {
                each.remove();
                removed = true;
            }
        }
        return removed;
    }
    boolean retainAll(java.util.Collection<?> c);
    void clear();
    boolean equals(Object o);
    int hashCode();
    @Override
    default Spliterator<E> spliterator() {
        return Spliterators.spliterator(this, 0);
    }
    default Stream<E> stream() {
        return StreamSupport.stream(spliterator(), false);
    }
    default Stream<E> parallelStream() {
        return StreamSupport.stream(spliterator(), true);
    }
}

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