Java Collection

public interface Collection<E> extends Iterable<E>{
  int size();

  boolean isEmpty();

  boolean contains(Object o);

  @NotNull Iterable<E> iterator();

  @NotNull @Flow(sourceContainer = true ,targetContainer = true) Object[] toArray();

  @NotNull @Flow(sourceContainer = true ,targetContainer = true) <T> T[] toArray(@NotNull T[] a);

  @Contract(mutates="this") boolean add(E e);

  @Contract(mutates="this") boolean remove(Object o);

  boolean containsAll(@NotNull Collection<?> c);

  @Contract(mutates="this") boolean addAll(@NotNull @Flow(sourceContainer = true, targetContainer = true) Collection<? extends E> c);

  @Contract(mutates="this") boolean removeAll(@NotNull Collection<?> c);

  @Contract(mutates="this") default boolean removeIf(Predicate<? super E> filter){
    Object.requireNonNull(filter);
    boolean removed = false;
    final Iterator<E> each = iterator();
    while(each.hasNext()){
      if(filter.test(each.next())){
        each.remove();
        removed = true;
      }
    }

    return removed;
  }

  @Contract(mutates="this") boolean retainAll(@NotNull Collection<?> c);

  @Contract(mutates="this") void clear();

  boolean equals(Object o);

  int hashCode();

  @Contract(pure=true) @Override
  default Spliterator<E> spliterator(){ return Spliterators.spliterator(this,0);}

  @Contract(pure=true)
  default Stream<E> stream() { return StreamSupport.stream(spliterator(),false);}

  @Contract(pure=true)
  default Stream<E> parallelStream(){ return StreamSupport.stream(spliterator(),true);}
}