Set 接口 源代码

Set 接口 源代码

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package java.util;

/**
 * A collection that contains no duplicate elements.  More formally, sets
 * contain no pair of elements <code>e1</code> and <code>e2</code> such that
 * <code>e1.equals(e2)</code>, and at most one null element.  As implied by
 * its name, this interface models the mathematical <i>set</i> abstraction.
 *
 * set不包含重复元素，不存在e1.equals(e2)，set最多有一个null值
 *
 * <p>The <tt>Set</tt> interface places additional stipulations, beyond those
 * inherited from the <tt>Collection</tt> interface, on the contracts of all
 * constructors and on the contracts of the <tt>add</tt>, <tt>equals</tt> and
 * <tt>hashCode</tt> methods.  Declarations for other inherited methods are
 * also included here for convenience.  (The specifications accompanying these
 * declarations have been tailored to the <tt>Set</tt> interface, but they do
 * not contain any additional stipulations.)
 *
 * <p>The additional stipulation on constructors is, not surprisingly,
 * that all constructors must create a set that contains no duplicate elements
 * (as defined above).
 *
 * <p>Note: Great care must be exercised if mutable objects are used as set
 * elements.  The behavior of a set is not specified if the value of an object
 * is changed in a manner that affects <tt>equals</tt> comparisons while the
 * object is an element in the set.  A special case of this prohibition is
 * that it is not permissible for a set to contain itself as an element.
 *
 * <p>Some set implementations have restrictions on the elements that
 * they may contain.  For example, some implementations prohibit null elements,
 * and some have restrictions on the types of their elements.  Attempting to
 * add an ineligible element throws an unchecked exception, typically
 * <tt>NullPointerException</tt> or <tt>ClassCastException</tt>.  Attempting
 * to query the presence of an ineligible element may throw an exception,
 * or it may simply return false; some implementations will exhibit the former
 * behavior and some will exhibit the latter.  More generally, attempting an
 * operation on an ineligible element whose completion would not result in
 * the insertion of an ineligible element into the set may throw an
 * exception or it may succeed, at the option of the implementation.
 * Such exceptions are marked as "optional" in the specification for this
 * interface.
 *
 * <p>This interface is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @param <E> the type of elements maintained by this set
 *
 * @author  Josh Bloch
 * @author  Neal Gafter
 * @see Collection
 * @see List
 * @see SortedSet
 * @see HashSet
 * @see TreeSet
 * @see AbstractSet
 * @see Collections#singleton(java.lang.Object)
 * @see Collections#EMPTY_SET
 * @since 1.2
 */
/*
一个不包含重复元素的 collection。更确切地讲，set 不包含满足 e1.equals(e2) 的元素对 e1 和 e2，
并且最多包含一个 null 元素。正如其名称所暗示的，此接口模仿了数学上的 set 抽象。

在所有构造方法以及 add、equals 和 hashCode 方法的协定上，Set 接口还加入了其他规定，
这些规定超出了从 Collection 接口所继承的内容。出于方便考虑，它还包括了其他继承方法的声明
（这些声明的规范已经专门针对 Set 接口进行了修改，但是没有包含任何其他的规定）。

对这些构造方法的其他规定是（不要奇怪），所有构造方法必须创建一个不包含重复元素的 set（正如上面所定义的）。

注：如果将可变对象用作 set 元素，那么必须极其小心。如果对象是 set 中某个元素，
以一种影响 equals 比较的方式改变对象的值，那么 set 的行为就是不确定的。此项禁止的
一个特殊情况是不允许某个 set 包含其自身作为元素。

某些 set 实现对其所包含的元素有所限制。例如，某些实现禁止 null 元素，而某些则对
其元素的类型所有限制。试图添加不合格的元素会抛出未经检查的异常，通常是 NullPointerException
或 ClassCastException。试图查询不合格的元素是否存在可能会抛出异常，也可能简单地返回 false；
某些实现会采用前一种行为，而某些则采用后者。概括地说，试图对不合格元素执行操作时，
如果完成该操作后不会导致在 set 中插入不合格的元素，则该操作可能抛出一个异常，也可能成功，
这取决于实现的选择。此接口的规范中将这样的异常标记为“可选”。
 */
public interface Set<E> extends Collection<E> {
    // Query Operations

    /**
     * Returns the number of elements in this set (its cardinality).  If this
     * set contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
     * <tt>Integer.MAX_VALUE</tt>.
     *
     * @return the number of elements in this set (its cardinality)
     */
    //返回容量，最大为Integer.MAX_VALUE
    int size();

    /**
     * Returns <tt>true</tt> if this set contains no elements.
     *
     * @return <tt>true</tt> if this set contains no elements
     */
    //是否没有元素
    boolean isEmpty();

    /**
     * Returns <tt>true</tt> if this set contains the specified element.
     * More formally, returns <tt>true</tt> if and only if this set
     * contains an element <tt>e</tt> such that
     * <tt>(o==null ? e==null : o.equals(e))</tt>.
     *
     * @param o element whose presence in this set is to be tested
     * @return <tt>true</tt> if this set contains the specified element
     * @throws ClassCastException if the type of the specified element
     *         is incompatible with this set
     * (<a href="Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified element is null and this
     *         set does not permit null elements
     * (<a href="Collection.html#optional-restrictions">optional</a>)
     */
    //判断是否包含元素o return o==null ? e==null : o.equals(e)
    boolean contains(Object o);

    /**
     * Returns an iterator over the elements in this set.  The elements are
     * returned in no particular order (unless this set is an instance of some
     * class that provides a guarantee).
     *
     * @return an iterator over the elements in this set
     */
    //返回容器的迭代器
    Iterator<E> iterator();

    /**
     * Returns an array containing all of the elements in this set.
     * If this set makes any guarantees as to what order its elements
     * are returned by its iterator, this method must return the
     * elements in the same order.
     *
     * <p>The returned array will be "safe" in that no references to it
     * are maintained by this set.  (In other words, this method must
     * allocate a new array even if this set is backed by an array).
     * The caller is thus free to modify the returned array.
     *
     * <p>This method acts as bridge between array-based and collection-based
     * APIs.
     *
     * @return an array containing all the elements in this set
     */
    //返回包含容器所有元素的数组
    Object[] toArray();

    /**
     * Returns an array containing all of the elements in this set; the
     * runtime type of the returned array is that of the specified array.
     * If the set fits in the specified array, it is returned therein.
     * Otherwise, a new array is allocated with the runtime type of the
     * specified array and the size of this set.
     *
     * <p>If this set fits in the specified array with room to spare
     * (i.e., the array has more elements than this set), the element in
     * the array immediately following the end of the set is set to
     * <tt>null</tt>.  (This is useful in determining the length of this
     * set <i>only</i> if the caller knows that this set does not contain
     * any null elements.)
     *
     * <p>If this set makes any guarantees as to what order its elements
     * are returned by its iterator, this method must return the elements
     * in the same order.
     *
     * <p>Like the {@link #toArray()} method, this method acts as bridge between
     * array-based and collection-based APIs.  Further, this method allows
     * precise control over the runtime type of the output array, and may,
     * under certain circumstances, be used to save allocation costs.
     *
     * <p>Suppose <tt>x</tt> is a set known to contain only strings.
     * The following code can be used to dump the set into a newly allocated
     * array of <tt>String</tt>:
     *
     * <pre>
     *     String[] y = x.toArray(new String[0]);</pre>
     *
     * Note that <tt>toArray(new Object[0])</tt> is identical in function to
     * <tt>toArray()</tt>.
     *
     * @param a the array into which the elements of this set are to be
     *        stored, if it is big enough; otherwise, a new array of the same
     *        runtime type is allocated for this purpose.
     * @return an array containing all the elements in this set
     * @throws ArrayStoreException if the runtime type of the specified array
     *         is not a supertype of the runtime type of every element in this
     *         set
     * @throws NullPointerException if the specified array is null
     */
    //返回T类的数组
    <T> T[] toArray(T[] a);


    // Modification Operations

    /**
     * Adds the specified element to this set if it is not already present
     * (optional operation).  More formally, adds the specified element
     * <tt>e</tt> to this set if the set contains no element <tt>e2</tt>
     * such that
     * <tt>(e==null ? e2==null : e.equals(e2))</tt>.
     * If this set already contains the element, the call leaves the set
     * unchanged and returns <tt>false</tt>.  In combination with the
     * restriction on constructors, this ensures that sets never contain
     * duplicate elements.
     *
     * <p>The stipulation above does not imply that sets must accept all
     * elements; sets may refuse to add any particular element, including
     * <tt>null</tt>, and throw an exception, as described in the
     * specification for {@link Collection#add Collection.add}.
     * Individual set implementations should clearly document any
     * restrictions on the elements that they may contain.
     *
     * @param e element to be added to this set
     * @return <tt>true</tt> if this set did not already contain the specified
     *         element
     * @throws UnsupportedOperationException if the <tt>add</tt> operation
     *         is not supported by this set
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this set
     * @throws NullPointerException if the specified element is null and this
     *         set does not permit null elements
     * @throws IllegalArgumentException if some property of the specified element
     *         prevents it from being added to this set
     */
    //添加元素e
    boolean add(E e);


    /**
     * Removes the specified element from this set if it is present
     * (optional operation).  More formally, removes an element <tt>e</tt>
     * such that
     * <tt>(o==null ? e==null : o.equals(e))</tt>, if
     * this set contains such an element.  Returns <tt>true</tt> if this set
     * contained the element (or equivalently, if this set changed as a
     * result of the call).  (This set will not contain the element once the
     * call returns.)
     *
     * @param o object to be removed from this set, if present
     * @return <tt>true</tt> if this set contained the specified element
     * @throws ClassCastException if the type of the specified element
     *         is incompatible with this set
     * (<a href="Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified element is null and this
     *         set does not permit null elements
     * (<a href="Collection.html#optional-restrictions">optional</a>)
     * @throws UnsupportedOperationException if the <tt>remove</tt> operation
     *         is not supported by this set
     */
    //移除掉容器中的o元素
    boolean remove(Object o);


    // Bulk Operations

    /**
     * Returns <tt>true</tt> if this set contains all of the elements of the
     * specified collection.  If the specified collection is also a set, this
     * method returns <tt>true</tt> if it is a <i>subset</i> of this set.
     *
     * @param  c collection to be checked for containment in this set
     * @return <tt>true</tt> if this set contains all of the elements of the
     *         specified collection
     * @throws ClassCastException if the types of one or more elements
     *         in the specified collection are incompatible with this
     *         set
     * (<a href="Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified collection contains one
     *         or more null elements and this set does not permit null
     *         elements
     * (<a href="Collection.html#optional-restrictions">optional</a>),
     *         or if the specified collection is null
     * @see    #contains(Object)
     */
    //判断容器是否包含所有c中的元素
    boolean containsAll(Collection<?> c);

    /**
     * Adds all of the elements in the specified collection to this set if
     * they're not already present (optional operation).  If the specified
     * collection is also a set, the <tt>addAll</tt> operation effectively
     * modifies this set so that its value is the <i>union</i> of the two
     * sets.  The behavior of this operation is undefined if the specified
     * collection is modified while the operation is in progress.
     *
     * @param  c collection containing elements to be added to this set
     * @return <tt>true</tt> if this set changed as a result of the call
     *
     * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
     *         is not supported by this set
     * @throws ClassCastException if the class of an element of the
     *         specified collection prevents it from being added to this set
     * @throws NullPointerException if the specified collection contains one
     *         or more null elements and this set does not permit null
     *         elements, or if the specified collection is null
     * @throws IllegalArgumentException if some property of an element of the
     *         specified collection prevents it from being added to this set
     * @see #add(Object)
     */
    //将c中所有元素添加到容器中
    boolean addAll(Collection<? extends E> c);

    /**
     * Retains only the elements in this set that are contained in the
     * specified collection (optional operation).  In other words, removes
     * from this set all of its elements that are not contained in the
     * specified collection.  If the specified collection is also a set, this
     * operation effectively modifies this set so that its value is the
     * <i>intersection</i> of the two sets.
     *
     * @param  c collection containing elements to be retained in this set
     * @return <tt>true</tt> if this set changed as a result of the call
     * @throws UnsupportedOperationException if the <tt>retainAll</tt> operation
     *         is not supported by this set
     * @throws ClassCastException if the class of an element of this set
     *         is incompatible with the specified collection
     * (<a href="Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if this set contains a null element and the
     *         specified collection does not permit null elements
     *         (<a href="Collection.html#optional-restrictions">optional</a>),
     *         or if the specified collection is null
     * @see #remove(Object)
     */
    //将本容器和c容器取交集
    boolean retainAll(Collection<?> c);

    /**
     * Removes from this set all of its elements that are contained in the
     * specified collection (optional operation).  If the specified
     * collection is also a set, this operation effectively modifies this
     * set so that its value is the <i>asymmetric set difference</i> of
     * the two sets.
     *
     * @param  c collection containing elements to be removed from this set
     * @return <tt>true</tt> if this set changed as a result of the call
     * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation
     *         is not supported by this set
     * @throws ClassCastException if the class of an element of this set
     *         is incompatible with the specified collection
     * (<a href="Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if this set contains a null element and the
     *         specified collection does not permit null elements
     *         (<a href="Collection.html#optional-restrictions">optional</a>),
     *         or if the specified collection is null
     * @see #remove(Object)
     * @see #contains(Object)
     */
    //移除所有在容器c中出现的元素
    boolean removeAll(Collection<?> c);

    /**
     * Removes all of the elements from this set (optional operation).
     * The set will be empty after this call returns.
     *
     * @throws UnsupportedOperationException if the <tt>clear</tt> method
     *         is not supported by this set
     */
    //清除掉容器中的元素
    void clear();


    // Comparison and hashing

    /**
     * Compares the specified object with this set for equality.  Returns
     * <tt>true</tt> if the specified object is also a set, the two sets
     * have the same size, and every member of the specified set is
     * contained in this set (or equivalently, every member of this set is
     * contained in the specified set).  This definition ensures that the
     * equals method works properly across different implementations of the
     * set interface.
     *
     * @param o object to be compared for equality with this set
     * @return <tt>true</tt> if the specified object is equal to this set
     */
    //元素与o是否相等
    boolean equals(Object o);

    /**
     * Returns the hash code value for this set.  The hash code of a set is
     * defined to be the sum of the hash codes of the elements in the set,
     * where the hash code of a <tt>null</tt> element is defined to be zero.
     * This ensures that <tt>s1.equals(s2)</tt> implies that
     * <tt>s1.hashCode()==s2.hashCode()</tt> for any two sets <tt>s1</tt>
     * and <tt>s2</tt>, as required by the general contract of
     * {@link Object#hashCode}.
     *
     * @return the hash code value for this set
     * @see Object#equals(Object)
     * @see Set#equals(Object)
     */
    //计算hash值 s1.hashCode() == s2.hashCode() 说明 s1.equals(s2)
    int hashCode();

    /**
     * Creates a {@code Spliterator} over the elements in this set.
     *
     * <p>The {@code Spliterator} reports {@link Spliterator#DISTINCT}.
     * Implementations should document the reporting of additional
     * characteristic values.
     *
     * @implSpec
     * The default implementation creates a
     * <em><a href="Spliterator.html#binding">late-binding</a></em> spliterator
     * from the set's {@code Iterator}.  The spliterator inherits the
     * <em>fail-fast</em> properties of the set's iterator.
     * <p>
     * The created {@code Spliterator} additionally reports
     * {@link Spliterator#SIZED}.
     *
     * @implNote
     * The created {@code Spliterator} additionally reports
     * {@link Spliterator#SUBSIZED}.
     *
     * @return a {@code Spliterator} over the elements in this set
     * @since 1.8
     */
    @Override
    default Spliterator<E> spliterator() {
        return Spliterators.spliterator(this, Spliterator.DISTINCT);
    }
}