集合的设计

在 Java 中，Collection 作为集合的顶层设计，一共抽象出了17个公共方法：

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

    boolean isEmpty();

    boolean contains(@RecentlyNullable Object var1);

    @RecentlyNonNull
    Iterator<E> iterator();

    @RecentlyNonNull
    Object[] toArray();

    @RecentlyNonNull
    <T> T[] toArray(@RecentlyNonNull T[] var1);

    @RecentlyNonNull
    default <T> T[] toArray(@RecentlyNonNull IntFunction<T[]> generator) {
        throw new RuntimeException("Stub!");
    }

    boolean add(E var1);

    boolean remove(@RecentlyNullable Object var1);

    boolean containsAll(@RecentlyNonNull Collection<?> var1);

    boolean addAll(@RecentlyNonNull Collection<? extends E> var1);

    boolean removeAll(@RecentlyNonNull Collection<?> var1);

    default boolean removeIf(@RecentlyNonNull Predicate<? super E> filter) {
        throw new RuntimeException("Stub!");
    }

    boolean retainAll(@RecentlyNonNull Collection<?> var1);

    void clear();

    boolean equals(@RecentlyNullable Object var1);

    int hashCode();

    @RecentlyNonNull
    default Spliterator<E> spliterator() {
        throw new RuntimeException("Stub!");
    }

    @RecentlyNonNull
    default Stream<E> stream() {
        throw new RuntimeException("Stub!");
    }

    @RecentlyNonNull
    default Stream<E> parallelStream() {
        throw new RuntimeException("Stub!");
    }
}

为了防止读起来特别痛苦，我们把以上方法做一些分类，大约可分为三类：修改操作、查询操作、批量操作