List 接口 源代码

/* * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved. * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. * * * * * * * * * * * * * * * * * * * * */package java.util;import java.util.function.UnaryOperator;/** * An ordered collection (also known as a <i>sequence</i>).  The user of this * interface has precise control over where in the list each element is * inserted.  The user can access elements by their integer index (position in * the list), and search for elements in the list.<p> * * Unlike sets, lists typically allow duplicate elements.  More formally, * lists typically allow pairs of elements <tt>e1</tt> and <tt>e2</tt> * such that <tt>e1.equals(e2)</tt>, and they typically allow multiple * null elements if they allow null elements at all.  It is not inconceivable * that someone might wish to implement a list that prohibits duplicates, by * throwing runtime exceptions when the user attempts to insert them, but we * expect this usage to be rare.<p> * * The <tt>List</tt> interface places additional stipulations, beyond those * specified in the <tt>Collection</tt> interface, on the contracts of the * <tt>iterator</tt>, <tt>add</tt>, <tt>remove</tt>, <tt>equals</tt>, and * <tt>hashCode</tt> methods.  Declarations for other inherited methods are * also included here for convenience.<p> * * The <tt>List</tt> interface provides four methods for positional (indexed) * access to list elements.  Lists (like Java arrays) are zero based.  Note * that these operations may execute in time proportional to the index value * for some implementations (the <tt>LinkedList</tt> class, for * example). Thus, iterating over the elements in a list is typically * preferable to indexing through it if the caller does not know the * implementation.<p> * * The <tt>List</tt> interface provides a special iterator, called a * <tt>ListIterator</tt>, that allows element insertion and replacement, and * bidirectional access in addition to the normal operations that the * <tt>Iterator</tt> interface provides.  A method is provided to obtain a * list iterator that starts at a specified position in the list.<p> * * The <tt>List</tt> interface provides two methods to search for a specified * object.  From a performance standpoint, these methods should be used with * caution.  In many implementations they will perform costly linear * searches.<p> * * The <tt>List</tt> interface provides two methods to efficiently insert and * remove multiple elements at an arbitrary point in the list.<p> * * Note: While it is permissible for lists to contain themselves as elements, * extreme caution is advised: the <tt>equals</tt> and <tt>hashCode</tt> * methods are no longer well defined on such a list. * * <p>Some list 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 list 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 in this list * * @author  Josh Bloch * @author  Neal Gafter * @see Collection * @see Set * @see ArrayList * @see LinkedList * @see Vector * @see Arrays#asList(Object[]) * @see Collections#nCopies(int, Object) * @see Collections#EMPTY_LIST * @see AbstractList * @see AbstractSequentialList * @since 1.2 *//*有序的 collection（也称为序列）。此接口的用户可以对列表中每个元素的插入位置进行精确地控制。用户可以根据元素的整数索引（在列表中的位置）访问元素，并搜索列表中的元素。与 set 不同，列表通常允许重复的元素。更确切地讲，列表通常允许满足 e1.equals(e2) 的元素对 e1 和 e2，并且如果列表本身允许 null 元素的话，通常它们允许多个 null 元素。难免有人希望通过在用户尝试插入重复元素时抛出运行时异常的方法来禁止重复的列表，但我们希望这种用法越少越好。List 接口在 iterator、add、remove、equals 和 hashCode 方法的协定上加了一些其他约定，超过了Collection 接口中指定的约定。为方便起见，这里也包括了其他继承方法的声明。List 接口提供了 4 种对列表元素进行定位（索引）访问方法。列表（像 Java 数组一样）是基于 0 的。注意，这些操作可能在和某些实现（例如 LinkedList 类）的索引值成比例的时间内执行。因此，如果调用者不知道实现，那么在列表元素上迭代通常优于用索引遍历列表。List 接口提供了特殊的迭代器，称为 ListIterator，除了允许 Iterator 接口提供的正常操作外，该迭代器还允许元素插入和替换，以及双向访问。还提供了一个方法来获取从列表中指定位置开始的列表迭代器。List 接口提供了两种搜索指定对象的方法。从性能的观点来看，应该小心使用这些方法。在很多实现中，它们将执行高开销的线性搜索。List 接口提供了两种在列表的任意位置高效插入和移除多个元素的方法。注意：尽管列表允许把自身作为元素包含在内，但建议要特别小心：在这样的列表上，equals 和 hashCode 方法不再是定义良好的。某些列表实现对列表可能包含的元素有限制。例如，某些实现禁止 null 元素，而某些实现则对元素的类型有限制。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列表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 List<E> extends Collection<E> {    // Query Operations    /**     * Returns the number of elements in this list.  If this list contains     * more than <tt>Integer.MAX_VALUE</tt> elements, returns     * <tt>Integer.MAX_VALUE</tt>.     *     * @return the number of elements in this list     */    //返回列表的元素个数，Math.min(xxx, Integer.MAX_VALUE)    int size();    /**     * Returns <tt>true</tt> if this list contains no elements.     *     * @return <tt>true</tt> if this list contains no elements     */    //如果容器没有元素，返回true    boolean isEmpty();    /**     * Returns <tt>true</tt> if this list contains the specified element.     * More formally, returns <tt>true</tt> if and only if this list contains     * at least one element <tt>e</tt> such that     * <tt>(o==null ? e==null : o.equals(e))</tt>.     *     * @param o element whose presence in this list is to be tested     * @return <tt>true</tt> if this list contains the specified element     * @throws ClassCastException if the type of the specified element     *         is incompatible with this list     * (<a href="Collection.html#optional-restrictions">optional</a>)     * @throws NullPointerException if the specified element is null and this     *         list does not permit null elements     * (<a href="Collection.html#optional-restrictions">optional</a>)     */    //返回true，说明容器包含o元素    boolean contains(Object o);    /**     * Returns an iterator over the elements in this list in proper sequence.     *     * @return an iterator over the elements in this list in proper sequence     */    //返回该包含列表元素的迭代器    Iterator<E> iterator();    /**     * Returns an array containing all of the elements in this list in proper     * sequence (from first to last element).     *     * <p>The returned array will be "safe" in that no references to it are     * maintained by this list.  (In other words, this method must     * allocate a new array even if this list 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 of the elements in this list in proper     *         sequence     * @see Arrays#asList(Object[])     */    //返回该列表元素组成的对象数组    Object[] toArray();    /**     * Returns an array containing all of the elements in this list in     * proper sequence (from first to last element); the runtime type of     * the returned array is that of the specified array.  If the list 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 list.     *     * <p>If the list fits in the specified array with room to spare (i.e.,     * the array has more elements than the list), the element in the array     * immediately following the end of the list is set to <tt>null</tt>.     * (This is useful in determining the length of the list <i>only</i> if     * the caller knows that the list does not contain any null elements.)     *     * <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 list known to contain only strings.     * The following code can be used to dump the list into a newly     * allocated array of <tt>String</tt>:     *     * <pre>{@code     *     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 list 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 the elements of this list     * @throws ArrayStoreException if the runtime type of the specified array     *         is not a supertype of the runtime type of every element in     *         this list     * @throws NullPointerException if the specified array is null     */    //返回该容器的数组对象，对象会经过转为T类型    <T> T[] toArray(T[] a);    // Modification Operations    /**     * Appends the specified element to the end of this list (optional     * operation).     *     * <p>Lists that support this operation may place limitations on what     * elements may be added to this list.  In particular, some     * lists will refuse to add null elements, and others will impose     * restrictions on the type of elements that may be added.  List     * classes should clearly specify in their documentation any restrictions     * on what elements may be added.     *     * @param e element to be appended to this list     * @return <tt>true</tt> (as specified by {@link Collection#add})     * @throws UnsupportedOperationException if the <tt>add</tt> operation     *         is not supported by this list     * @throws ClassCastException if the class of the specified element     *         prevents it from being added to this list     * @throws NullPointerException if the specified element is null and this     *         list does not permit null elements     * @throws IllegalArgumentException if some property of this element     *         prevents it from being added to this list     */    //往列表中添加元素，可能会对添加的元素做限制，比如添加的元素不为null    boolean add(E e);    /**     * Removes the first occurrence of the specified element from this list,     * if it is present (optional operation).  If this list does not contain     * the element, it is unchanged.  More formally, removes the element with     * the lowest index <tt>i</tt> such that     * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>     * (if such an element exists).  Returns <tt>true</tt> if this list     * contained the specified element (or equivalently, if this list changed     * as a result of the call).     *     * @param o element to be removed from this list, if present     * @return <tt>true</tt> if this list contained the specified element     * @throws ClassCastException if the type of the specified element     *         is incompatible with this list     * (<a href="Collection.html#optional-restrictions">optional</a>)     * @throws NullPointerException if the specified element is null and this     *         list 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 list     */    //列表中移除掉元素o    boolean remove(Object o);    // Bulk Modification Operations    /**     * Returns <tt>true</tt> if this list contains all of the elements of the     * specified collection.     *     * @param  c collection to be checked for containment in this list     * @return <tt>true</tt> if this list 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     *         list     * (<a href="Collection.html#optional-restrictions">optional</a>)     * @throws NullPointerException if the specified collection contains one     *         or more null elements and this list does not permit null     *         elements     *         (<a href="Collection.html#optional-restrictions">optional</a>),     *         or if the specified collection is null     * @see #contains(Object)     */    //列表中包含容器c中所有元素，则返回true    boolean containsAll(Collection<?> c);    /**     * Appends all of the elements in the specified collection to the end of     * this list, in the order that they are returned by the specified     * collection's iterator (optional operation).  The behavior of this     * operation is undefined if the specified collection is modified while     * the operation is in progress.  (Note that this will occur if the     * specified collection is this list, and it's nonempty.)     *     * @param c collection containing elements to be added to this list     * @return <tt>true</tt> if this list changed as a result of the call     * @throws UnsupportedOperationException if the <tt>addAll</tt> operation     *         is not supported by this list     * @throws ClassCastException if the class of an element of the specified     *         collection prevents it from being added to this list     * @throws NullPointerException if the specified collection contains one     *         or more null elements and this list 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 list     * @see #add(Object)     */    //列表中添加包含在容器c中的所有元素    boolean addAll(Collection<? extends E> c);    /**     * Inserts all of the elements in the specified collection into this     * list at the specified position (optional operation).  Shifts the     * element currently at that position (if any) and any subsequent     * elements to the right (increases their indices).  The new elements     * will appear in this list in the order that they are returned by the     * specified collection's iterator.  The behavior of this operation is     * undefined if the specified collection is modified while the     * operation is in progress.  (Note that this will occur if the specified     * collection is this list, and it's nonempty.)     *     * @param index index at which to insert the first element from the     *              specified collection     * @param c collection containing elements to be added to this list     * @return <tt>true</tt> if this list changed as a result of the call     * @throws UnsupportedOperationException if the <tt>addAll</tt> operation     *         is not supported by this list     * @throws ClassCastException if the class of an element of the specified     *         collection prevents it from being added to this list     * @throws NullPointerException if the specified collection contains one     *         or more null elements and this list 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 list     * @throws IndexOutOfBoundsException if the index is out of range     *         (<tt>index < 0 || index > size()</tt>)     */    //列表中添加容器c中的元素，容器c的第一个元素存放在下标为index的位置，后面依次递增    boolean addAll(int index, Collection<? extends E> c);    /**     * Removes from this list all of its elements that are contained in the     * specified collection (optional operation).     *     * @param c collection containing elements to be removed from this list     * @return <tt>true</tt> if this list changed as a result of the call     * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation     *         is not supported by this list     * @throws ClassCastException if the class of an element of this list     *         is incompatible with the specified collection     * (<a href="Collection.html#optional-restrictions">optional</a>)     * @throws NullPointerException if this list 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)     */    //列表中移除所有在容器c中的元素    boolean removeAll(Collection<?> c);    /**     * Retains only the elements in this list that are contained in the     * specified collection (optional operation).  In other words, removes     * from this list all of its elements that are not contained in the     * specified collection.     *     * @param c collection containing elements to be retained in this list     * @return <tt>true</tt> if this list changed as a result of the call     * @throws UnsupportedOperationException if the <tt>retainAll</tt> operation     *         is not supported by this list     * @throws ClassCastException if the class of an element of this list     *         is incompatible with the specified collection     * (<a href="Collection.html#optional-restrictions">optional</a>)     * @throws NullPointerException if this list 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)     */    //调用此方法，移除所有不存在容器c中的元素，也就是求列表和c的交集    boolean retainAll(Collection<?> c);    /**     * Replaces each element of this list with the result of applying the     * operator to that element.  Errors or runtime exceptions thrown by     * the operator are relayed to the caller.     *     * @implSpec     * The default implementation is equivalent to, for this {@code list}:     * <pre>{@code     *     final ListIterator<E> li = list.listIterator();     *     while (li.hasNext()) {     *         li.set(operator.apply(li.next()));     *     }     * }</pre>     *     * If the list's list-iterator does not support the {@code set} operation     * then an {@code UnsupportedOperationException} will be thrown when     * replacing the first element.     *     * @param operator the operator to apply to each element     * @throws UnsupportedOperationException if this list is unmodifiable.     *         Implementations may throw this exception if an element     *         cannot be replaced or if, in general, modification is not     *         supported     * @throws NullPointerException if the specified operator is null or     *         if the operator result is a null value and this list does     *         not permit null elements     *         (<a href="Collection.html#optional-restrictions">optional</a>)     * @since 1.8     */    default void replaceAll(UnaryOperator<E> operator) {        Objects.requireNonNull(operator);        final ListIterator<E> li = this.listIterator();        while (li.hasNext()) {            li.set(operator.apply(li.next()));        }    }    /**     * Sorts this list using the supplied {@code Comparator} to compare elements.     *     * @implSpec     * The default implementation is equivalent to, for this {@code list}:     * <pre>Collections.sort(list, c)</pre>     *     * @param c the {@code Comparator} used to compare list elements.     *          A {@code null} value indicates that the elements'     *          {@linkplain Comparable natural ordering} should be used     * @throws ClassCastException if the list contains elements that are not     *         <i>mutually comparable</i> using the specified comparator     * @throws UnsupportedOperationException if the list's list-iterator does     *         not support the {@code set} operation     * @throws IllegalArgumentException     *         (<a href="Collection.html#optional-restrictions">optional</a>)     *         if the comparator is found to violate the {@link Comparator}     *         contract     * @since 1.8     */    //通过参数传入比较器，根据比较器来为列表排序    default void sort(Comparator<? super E> c) {        Collections.sort(this, c);    }    /**     * Removes all of the elements from this list (optional operation).     * The list will be empty after this call returns.     *     * @throws UnsupportedOperationException if the <tt>clear</tt> operation     *         is not supported by this list     */    //清除所有元素    void clear();    // Comparison and hashing    /**     * Compares the specified object with this list for equality.  Returns     * <tt>true</tt> if and only if the specified object is also a list, both     * lists have the same size, and all corresponding pairs of elements in     * the two lists are <i>equal</i>.  (Two elements <tt>e1</tt> and     * <tt>e2</tt> are <i>equal</i> if <tt>(e1==null ? e2==null :     * e1.equals(e2))</tt>.)  In other words, two lists are defined to be     * equal if they contain the same elements in the same order.  This     * definition ensures that the equals method works properly across     * different implementations of the <tt>List</tt> interface.     *     * @param o the object to be compared for equality with this list     * @return <tt>true</tt> if the specified object is equal to this list     */    boolean equals(Object o);    /**     * Returns the hash code value for this list.  The hash code of a list     * is defined to be the result of the following calculation:     * <pre>{@code     *     int hashCode = 1;     *     for (E e : list)     *         hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());     * }</pre>     * This ensures that <tt>list1.equals(list2)</tt> implies that     * <tt>list1.hashCode()==list2.hashCode()</tt> for any two lists,     * <tt>list1</tt> and <tt>list2</tt>, as required by the general     * contract of {@link Object#hashCode}.     *     * @return the hash code value for this list     * @see Object#equals(Object)     * @see #equals(Object)     */    int hashCode();    // Positional Access Operations    /**     * Returns the element at the specified position in this list.     *     * @param index index of the element to return     * @return the element at the specified position in this list     * @throws IndexOutOfBoundsException if the index is out of range     *         (<tt>index < 0 || index >= size()</tt>)     */    E get(int index);    /**     * Replaces the element at the specified position in this list with the     * specified element (optional operation).     *     * @param index index of the element to replace     * @param element element to be stored at the specified position     * @return the element previously at the specified position     * @throws UnsupportedOperationException if the <tt>set</tt> operation     *         is not supported by this list     * @throws ClassCastException if the class of the specified element     *         prevents it from being added to this list     * @throws NullPointerException if the specified element is null and     *         this list does not permit null elements     * @throws IllegalArgumentException if some property of the specified     *         element prevents it from being added to this list     * @throws IndexOutOfBoundsException if the index is out of range     *         (<tt>index < 0 || index >= size()</tt>)     */    //在列表下标为index的元素替换为element    E set(int index, E element);    /**     * Inserts the specified element at the specified position in this list     * (optional operation).  Shifts the element currently at that position     * (if any) and any subsequent elements to the right (adds one to their     * indices).     *     * @param index index at which the specified element is to be inserted     * @param element element to be inserted     * @throws UnsupportedOperationException if the <tt>add</tt> operation     *         is not supported by this list     * @throws ClassCastException if the class of the specified element     *         prevents it from being added to this list     * @throws NullPointerException if the specified element is null and     *         this list does not permit null elements     * @throws IllegalArgumentException if some property of the specified     *         element prevents it from being added to this list     * @throws IndexOutOfBoundsException if the index is out of range     *         (<tt>index < 0 || index > size()</tt>)     */    //将element插入到列表下标index的位置，后面如果有元素则往后移    void add(int index, E element);    /**     * Removes the element at the specified position in this list (optional     * operation).  Shifts any subsequent elements to the left (subtracts one     * from their indices).  Returns the element that was removed from the     * list.     *     * @param index the index of the element to be removed     * @return the element previously at the specified position     * @throws UnsupportedOperationException if the <tt>remove</tt> operation     *         is not supported by this list     * @throws IndexOutOfBoundsException if the index is out of range     *         (<tt>index < 0 || index >= size()</tt>)     */    //移除掉下标为index的元素，后面有元素的话往前移    E remove(int index);    // Search Operations    /**     * Returns the index of the first occurrence of the specified element     * in this list, or -1 if this list does not contain the element.     * More formally, returns the lowest index <tt>i</tt> such that     * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,     * or -1 if there is no such index.     *     * @param o element to search for     * @return the index of the first occurrence of the specified element in     *         this list, or -1 if this list does not contain the element     * @throws ClassCastException if the type of the specified element     *         is incompatible with this list     *         (<a href="Collection.html#optional-restrictions">optional</a>)     * @throws NullPointerException if the specified element is null and this     *         list does not permit null elements     *         (<a href="Collection.html#optional-restrictions">optional</a>)     */    //返回o出现在列表中的第一个位置的下标 返回-1表示列表没有o元素    int indexOf(Object o);    /**     * Returns the index of the last occurrence of the specified element     * in this list, or -1 if this list does not contain the element.     * More formally, returns the highest index <tt>i</tt> such that     * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,     * or -1 if there is no such index.     *     * @param o element to search for     * @return the index of the last occurrence of the specified element in     *         this list, or -1 if this list does not contain the element     * @throws ClassCastException if the type of the specified element     *         is incompatible with this list     *         (<a href="Collection.html#optional-restrictions">optional</a>)     * @throws NullPointerException if the specified element is null and this     *         list does not permit null elements     *         (<a href="Collection.html#optional-restrictions">optional</a>)     */    //返回o出现在列表中的最后一个位置的下标 返回-1表示列表没有o元素    int lastIndexOf(Object o);    // List Iterators    /**     * Returns a list iterator over the elements in this list (in proper     * sequence).     *     * @return a list iterator over the elements in this list (in proper     *         sequence)     */    //返回列表迭代器    ListIterator<E> listIterator();    /**     * Returns a list iterator over the elements in this list (in proper     * sequence), starting at the specified position in the list.     * The specified index indicates the first element that would be     * returned by an initial call to {@link ListIterator#next next}.     * An initial call to {@link ListIterator#previous previous} would     * return the element with the specified index minus one.     *     * @param index index of the first element to be returned from the     *        list iterator (by a call to {@link ListIterator#next next})     * @return a list iterator over the elements in this list (in proper     *         sequence), starting at the specified position in the list     * @throws IndexOutOfBoundsException if the index is out of range     *         ({@code index < 0 || index > size()})     */    //返回列表中元素的列表迭代器（按适当顺序），从列表的指定位置开始。指定的索引表示 next 的    // 初始调用所返回的第一个元素。previous 方法的初始调用将返回索引比指定索引少 1 的元素    ListIterator<E> listIterator(int index);    // View    /**     * Returns a view of the portion of this list between the specified     * <tt>fromIndex</tt>, inclusive, and <tt>toIndex</tt>, exclusive.  (If     * <tt>fromIndex</tt> and <tt>toIndex</tt> are equal, the returned list is     * empty.)  The returned list is backed by this list, so non-structural     * changes in the returned list are reflected in this list, and vice-versa.     * The returned list supports all of the optional list operations supported     * by this list.<p>     *     * This method eliminates the need for explicit range operations (of     * the sort that commonly exist for arrays).  Any operation that expects     * a list can be used as a range operation by passing a subList view     * instead of a whole list.  For example, the following idiom     * removes a range of elements from a list:     * <pre>{@code     *      list.subList(from, to).clear();     * }</pre>     * Similar idioms may be constructed for <tt>indexOf</tt> and     * <tt>lastIndexOf</tt>, and all of the algorithms in the     * <tt>Collections</tt> class can be applied to a subList.<p>     *     * The semantics of the list returned by this method become undefined if     * the backing list (i.e., this list) is <i>structurally modified</i> in     * any way other than via the returned list.  (Structural modifications are     * those that change the size of this list, or otherwise perturb it in such     * a fashion that iterations in progress may yield incorrect results.)     *     * @param fromIndex low endpoint (inclusive) of the subList     * @param toIndex high endpoint (exclusive) of the subList     * @return a view of the specified range within this list     * @throws IndexOutOfBoundsException for an illegal endpoint index value     *         (<tt>fromIndex < 0 || toIndex > size ||     *         fromIndex > toIndex</tt>)     */    //返回子列表 下标范围：[fromIndex, toIndex)    List<E> subList(int fromIndex, int toIndex);    /**     * Creates a {@link Spliterator} over the elements in this list.     *     * <p>The {@code Spliterator} reports {@link Spliterator#SIZED} and     * {@link Spliterator#ORDERED}.  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 list's {@code Iterator}.  The spliterator inherits the     * <em>fail-fast</em> properties of the list's iterator.     *     * @implNote     * The created {@code Spliterator} additionally reports     * {@link Spliterator#SUBSIZED}.     *     * @return a {@code Spliterator} over the elements in this list     * @since 1.8     */    @Override    default Spliterator<E> spliterator() {        return Spliterators.spliterator(this, Spliterator.ORDERED);    }}