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@ZeroGeek 2015-08-18T05:52:16.000000Z 字数 25339 阅读 530

ArrayList源码解析

Java 集合

transient 关键字

用来保护数据不被序列化（主要限于Serializable，其它方式无效），详情自行google。

jdk 版本：1.7.0_55

  1. public class ArrayList<E> extends AbstractList<E>
  2.         implements List<E>, RandomAccess, Cloneable, java.io.Serializable
  3. {
  4.     private static final long serialVersionUID = 8683452581122892189L;
  6.     /**
  7.      * 默认容量.
  8.      */
  9.     private static final int DEFAULT_CAPACITY = 10;
  11.     /**
  12.      * Shared empty array instance used for empty instances.
  13.      */
  14.     private static final Object[] EMPTY_ELEMENTDATA = {};
  16.     /**
  17.      * The array buffer into which the elements of the ArrayList are stored.
  18.      * The capacity of the ArrayList is the length of this array buffer. Any
  19.      * empty ArrayList with elementData == EMPTY_ELEMENTDATA will be expanded to
  20.      * DEFAULT_CAPACITY when the first element is added.
  21.      */
  22.     private transient Object[] elementData;
  24.     /**
  25.      * The size of the ArrayList (the number of elements it contains).
  26.      *
  27.      * @serial
  28.      */
  29.     private int size;
  31.     /**
  32.      * Constructs an empty list with the specified initial capacity.
  33.      *
  34.      * @param  initialCapacity  the initial capacity of the list
  35.      * @throws IllegalArgumentException if the specified initial capacity
  36.      *         is negative
  37.      */
  38.     public ArrayList(int initialCapacity) {
  39.         super();
  40.         if (initialCapacity < 0)
  41.             throw new IllegalArgumentException("Illegal Capacity: "+
  42.                                                initialCapacity);
  43.         this.elementData = new Object[initialCapacity];
  44.     }
  46.     /**
  47.      * Constructs an empty list with an initial capacity of ten.
  48.      */
  49.     public ArrayList() {
  50.         super();
  51.         this.elementData = EMPTY_ELEMENTDATA;
  52.     }
  54.     /**
  55.      * Constructs a list containing the elements of the specified
  56.      * collection, in the order they are returned by the collection's
  57.      * iterator.
  58.      *
  59.      * @param c the collection whose elements are to be placed into this list
  60.      * @throws NullPointerException if the specified collection is null
  61.      */
  62.     public ArrayList(Collection<? extends E> c) {
  63.         elementData = c.toArray();
  64.         size = elementData.length;
  65.         // c.toArray might (incorrectly) not return Object[] (see 6260652)
  66.         if (elementData.getClass() != Object[].class)
  67.             elementData = Arrays.copyOf(elementData, size, Object[].class);
  68.     }
  70.     /**
  71.      * Trims the capacity of this <tt>ArrayList</tt> instance to be the
  72.      * list's current size.  An application can use this operation to minimize
  73.      * the storage of an <tt>ArrayList</tt> instance.
  74.      */
  75.     public void trimToSize() {
  76.         modCount++;
  77.         if (size < elementData.length) {
  78.             elementData = Arrays.copyOf(elementData, size);
  79.         }
  80.     }
  82.     /**
  83.      * Increases the capacity of this <tt>ArrayList</tt> instance, if
  84.      * necessary, to ensure that it can hold at least the number of elements
  85.      * specified by the minimum capacity argument.
  86.      *
  87.      * @param   minCapacity   the desired minimum capacity
  88.      */
  89.     public void ensureCapacity(int minCapacity) {
  90.         int minExpand = (elementData != EMPTY_ELEMENTDATA)
  91.             // any size if real element table
  92.             ? 0
  93.             // larger than default for empty table. It's already supposed to be
  94.             // at default size.
  95.             : DEFAULT_CAPACITY;
  97.         if (minCapacity > minExpand) {
  98.             ensureExplicitCapacity(minCapacity);
  99.         }
  100.     }
  102.     private void ensureCapacityInternal(int minCapacity) {
  103.         if (elementData == EMPTY_ELEMENTDATA) {
  104.             minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
  105.         }
  107.         ensureExplicitCapacity(minCapacity);
  108.     }
  110.     private void ensureExplicitCapacity(int minCapacity) {
  111.         modCount++;
  113.         // overflow-conscious code
  114.         if (minCapacity - elementData.length > 0)
  115.             grow(minCapacity);
  116.     }
  118.     /**
  119.      * The maximum size of array to allocate.
  120.      * Some VMs reserve some header words in an array.
  121.      * Attempts to allocate larger arrays may result in
  122.      * OutOfMemoryError: Requested array size exceeds VM limit
  123.      */
  124.     private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
  126.     /**
  127.      * Increases the capacity to ensure that it can hold at least the
  128.      * number of elements specified by the minimum capacity argument.
  129.      *
  130.      * @param minCapacity the desired minimum capacity
  131.      */
  132.     private void grow(int minCapacity) {
  133.         // overflow-conscious code
  134.         int oldCapacity = elementData.length;
  135.         int newCapacity = oldCapacity + (oldCapacity >> 1);
  136.         if (newCapacity - minCapacity < 0)
  137.             newCapacity = minCapacity;
  138.         if (newCapacity - MAX_ARRAY_SIZE > 0)
  139.             newCapacity = hugeCapacity(minCapacity);
  140.         // minCapacity is usually close to size, so this is a win:
  141.         elementData = Arrays.copyOf(elementData, newCapacity);
  142.     }
  144.     private static int hugeCapacity(int minCapacity) {
  145.         if (minCapacity < 0) // overflow
  146.             throw new OutOfMemoryError();
  147.         return (minCapacity > MAX_ARRAY_SIZE) ?
  148.             Integer.MAX_VALUE :
  149.             MAX_ARRAY_SIZE;
  150.     }
  152.     /**
  153.      * Returns the number of elements in this list.
  154.      *
  155.      * @return the number of elements in this list
  156.      */
  157.     public int size() {
  158.         return size;
  159.     }
  161.     /**
  162.      * Returns <tt>true</tt> if this list contains no elements.
  163.      *
  164.      * @return <tt>true</tt> if this list contains no elements
  165.      */
  166.     public boolean isEmpty() {
  167.         return size == 0;
  168.     }
  170.     /**
  171.      * Returns <tt>true</tt> if this list contains the specified element.
  172.      * More formally, returns <tt>true</tt> if and only if this list contains
  173.      * at least one element <tt>e</tt> such that
  174.      * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
  175.      *
  176.      * @param o element whose presence in this list is to be tested
  177.      * @return <tt>true</tt> if this list contains the specified element
  178.      */
  179.     public boolean contains(Object o) {
  180.         return indexOf(o) >= 0;
  181.     }
  183.     /**
  184.      * Returns the index of the first occurrence of the specified element
  185.      * in this list, or -1 if this list does not contain the element.
  186.      * More formally, returns the lowest index <tt>i</tt> such that
  187.      * <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>,
  188.      * or -1 if there is no such index.
  189.      */
  190.     public int indexOf(Object o) {
  191.         if (o == null) {
  192.             for (int i = 0; i < size; i++)
  193.                 if (elementData[i]==null)
  194.                     return i;
  195.         } else {
  196.             for (int i = 0; i < size; i++)
  197.                 if (o.equals(elementData[i]))
  198.                     return i;
  199.         }
  200.         return -1;
  201.     }
  203.     /**
  204.      * Returns the index of the last occurrence of the specified element
  205.      * in this list, or -1 if this list does not contain the element.
  206.      * More formally, returns the highest index <tt>i</tt> such that
  207.      * <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>,
  208.      * or -1 if there is no such index.
  209.      */
  210.     public int lastIndexOf(Object o) {
  211.         if (o == null) {
  212.             for (int i = size-1; i >= 0; i--)
  213.                 if (elementData[i]==null)
  214.                     return i;
  215.         } else {
  216.             for (int i = size-1; i >= 0; i--)
  217.                 if (o.equals(elementData[i]))
  218.                     return i;
  219.         }
  220.         return -1;
  221.     }
  223.     /**
  224.      * Returns a shallow copy of this <tt>ArrayList</tt> instance.  (The
  225.      * elements themselves are not copied.)
  226.      *
  227.      * @return a clone of this <tt>ArrayList</tt> instance
  228.      */
  229.     public Object clone() {
  230.         try {
  231.             @SuppressWarnings("unchecked")
  232.                 ArrayList<E> v = (ArrayList<E>) super.clone();
  233.             v.elementData = Arrays.copyOf(elementData, size);
  234.             v.modCount = 0;
  235.             return v;
  236.         } catch (CloneNotSupportedException e) {
  237.             // this shouldn't happen, since we are Cloneable
  238.             throw new InternalError();
  239.         }
  240.     }
  242.     /**
  243.      * Returns an array containing all of the elements in this list
  244.      * in proper sequence (from first to last element).
  245.      *
  246.      * <p>The returned array will be "safe" in that no references to it are
  247.      * maintained by this list.  (In other words, this method must allocate
  248.      * a new array).  The caller is thus free to modify the returned array.
  249.      *
  250.      * <p>This method acts as bridge between array-based and collection-based
  251.      * APIs.
  252.      *
  253.      * @return an array containing all of the elements in this list in
  254.      *         proper sequence
  255.      */
  256.     public Object[] toArray() {
  257.         return Arrays.copyOf(elementData, size);
  258.     }
  260.     /**
  261.      * Returns an array containing all of the elements in this list in proper
  262.      * sequence (from first to last element); the runtime type of the returned
  263.      * array is that of the specified array.  If the list fits in the
  264.      * specified array, it is returned therein.  Otherwise, a new array is
  265.      * allocated with the runtime type of the specified array and the size of
  266.      * this list.
  267.      *
  268.      * <p>If the list fits in the specified array with room to spare
  269.      * (i.e., the array has more elements than the list), the element in
  270.      * the array immediately following the end of the collection is set to
  271.      * <tt>null</tt>.  (This is useful in determining the length of the
  272.      * list <i>only</i> if the caller knows that the list does not contain
  273.      * any null elements.)
  274.      *
  275.      * @param a the array into which the elements of the list are to
  276.      *          be stored, if it is big enough; otherwise, a new array of the
  277.      *          same runtime type is allocated for this purpose.
  278.      * @return an array containing the elements of the list
  279.      * @throws ArrayStoreException if the runtime type of the specified array
  280.      *         is not a supertype of the runtime type of every element in
  281.      *         this list
  282.      * @throws NullPointerException if the specified array is null
  283.      */
  284.     @SuppressWarnings("unchecked")
  285.     public <T> T[] toArray(T[] a) {
  286.         if (a.length < size)
  287.             // Make a new array of a's runtime type, but my contents:
  288.             return (T[]) Arrays.copyOf(elementData, size, a.getClass());
  289.         System.arraycopy(elementData, 0, a, 0, size);
  290.         if (a.length > size)
  291.             a[size] = null;
  292.         return a;
  293.     }
  295.     // Positional Access Operations
  297.     @SuppressWarnings("unchecked")
  298.     E elementData(int index) {
  299.         return (E) elementData[index];
  300.     }
  302.     /**
  303.      * Returns the element at the specified position in this list.
  304.      *
  305.      * @param  index index of the element to return
  306.      * @return the element at the specified position in this list
  307.      * @throws IndexOutOfBoundsException {@inheritDoc}
  308.      */
  309.     public E get(int index) {
  310.         rangeCheck(index);
  312.         return elementData(index);
  313.     }
  315.     /**
  316.      * Replaces the element at the specified position in this list with
  317.      * the specified element.
  318.      *
  319.      * @param index index of the element to replace
  320.      * @param element element to be stored at the specified position
  321.      * @return the element previously at the specified position
  322.      * @throws IndexOutOfBoundsException {@inheritDoc}
  323.      */
  324.     public E set(int index, E element) {
  325.         rangeCheck(index);
  327.         E oldValue = elementData(index);
  328.         elementData[index] = element;
  329.         return oldValue;
  330.     }
  332.     /**
  333.      * Appends the specified element to the end of this list.
  334.      *
  335.      * @param e element to be appended to this list
  336.      * @return <tt>true</tt> (as specified by {@link Collection#add})
  337.      */
  338.     public boolean add(E e) {
  339.         ensureCapacityInternal(size + 1);  // Increments modCount!!
  340.         elementData[size++] = e;
  341.         return true;
  342.     }
  344.     /**
  345.      * Inserts the specified element at the specified position in this
  346.      * list. Shifts the element currently at that position (if any) and
  347.      * any subsequent elements to the right (adds one to their indices).
  348.      *
  349.      * @param index index at which the specified element is to be inserted
  350.      * @param element element to be inserted
  351.      * @throws IndexOutOfBoundsException {@inheritDoc}
  352.      */
  353.     public void add(int index, E element) {
  354.         rangeCheckForAdd(index);
  356.         ensureCapacityInternal(size + 1);  // Increments modCount!!
  357.         System.arraycopy(elementData, index, elementData, index + 1,
  358.                          size - index);
  359.         elementData[index] = element;
  360.         size++;
  361.     }
  363.     /**
  364.      * Removes the element at the specified position in this list.
  365.      * Shifts any subsequent elements to the left (subtracts one from their
  366.      * indices).
  367.      *
  368.      * @param index the index of the element to be removed
  369.      * @return the element that was removed from the list
  370.      * @throws IndexOutOfBoundsException {@inheritDoc}
  371.      */
  372.     public E remove(int index) {
  373.         rangeCheck(index);
  375.         modCount++;
  376.         E oldValue = elementData(index);
  378.         int numMoved = size - index - 1;
  379.         if (numMoved > 0)
  380.             System.arraycopy(elementData, index+1, elementData, index,
  381.                              numMoved);
  382.         elementData[--size] = null; // clear to let GC do its work
  384.         return oldValue;
  385.     }
  387.     /**
  388.      * Removes the first occurrence of the specified element from this list,
  389.      * if it is present.  If the list does not contain the element, it is
  390.      * unchanged.  More formally, removes the element with the lowest index
  391.      * <tt>i</tt> such that
  392.      * <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>
  393.      * (if such an element exists).  Returns <tt>true</tt> if this list
  394.      * contained the specified element (or equivalently, if this list
  395.      * changed as a result of the call).
  396.      *
  397.      * @param o element to be removed from this list, if present
  398.      * @return <tt>true</tt> if this list contained the specified element
  399.      */
  400.     public boolean remove(Object o) {
  401.         if (o == null) {
  402.             for (int index = 0; index < size; index++)
  403.                 if (elementData[index] == null) {
  404.                     fastRemove(index);
  405.                     return true;
  406.                 }
  407.         } else {
  408.             for (int index = 0; index < size; index++)
  409.                 if (o.equals(elementData[index])) {
  410.                     fastRemove(index);
  411.                     return true;
  412.                 }
  413.         }
  414.         return false;
  415.     }
  417.     /*
  418.      * Private remove method that skips bounds checking and does not
  419.      * return the value removed.
  420.      */
  421.     private void fastRemove(int index) {
  422.         modCount++;
  423.         int numMoved = size - index - 1;
  424.         if (numMoved > 0)
  425.             System.arraycopy(elementData, index+1, elementData, index,
  426.                              numMoved);
  427.         elementData[--size] = null; // clear to let GC do its work
  428.     }
  430.     /**
  431.      * Removes all of the elements from this list.  The list will
  432.      * be empty after this call returns.
  433.      */
  434.     public void clear() {
  435.         modCount++;
  437.         // clear to let GC do its work
  438.         for (int i = 0; i < size; i++)
  439.             elementData[i] = null;
  441.         size = 0;
  442.     }
  444.     /**
  445.      * Appends all of the elements in the specified collection to the end of
  446.      * this list, in the order that they are returned by the
  447.      * specified collection's Iterator.  The behavior of this operation is
  448.      * undefined if the specified collection is modified while the operation
  449.      * is in progress.  (This implies that the behavior of this call is
  450.      * undefined if the specified collection is this list, and this
  451.      * list is nonempty.)
  452.      *
  453.      * @param c collection containing elements to be added to this list
  454.      * @return <tt>true</tt> if this list changed as a result of the call
  455.      * @throws NullPointerException if the specified collection is null
  456.      */
  457.     public boolean addAll(Collection<? extends E> c) {
  458.         Object[] a = c.toArray();
  459.         int numNew = a.length;
  460.         ensureCapacityInternal(size + numNew);  // Increments modCount
  461.         System.arraycopy(a, 0, elementData, size, numNew);
  462.         size += numNew;
  463.         return numNew != 0;
  464.     }
  466.     /**
  467.      * Inserts all of the elements in the specified collection into this
  468.      * list, starting at the specified position.  Shifts the element
  469.      * currently at that position (if any) and any subsequent elements to
  470.      * the right (increases their indices).  The new elements will appear
  471.      * in the list in the order that they are returned by the
  472.      * specified collection's iterator.
  473.      *
  474.      * @param index index at which to insert the first element from the
  475.      *              specified collection
  476.      * @param c collection containing elements to be added to this list
  477.      * @return <tt>true</tt> if this list changed as a result of the call
  478.      * @throws IndexOutOfBoundsException {@inheritDoc}
  479.      * @throws NullPointerException if the specified collection is null
  480.      */
  481.     public boolean addAll(int index, Collection<? extends E> c) {
  482.         rangeCheckForAdd(index);
  484.         Object[] a = c.toArray();
  485.         int numNew = a.length;
  486.         ensureCapacityInternal(size + numNew);  // Increments modCount
  488.         int numMoved = size - index;
  489.         if (numMoved > 0)
  490.             System.arraycopy(elementData, index, elementData, index + numNew,
  491.                              numMoved);
  493.         System.arraycopy(a, 0, elementData, index, numNew);
  494.         size += numNew;
  495.         return numNew != 0;
  496.     }
  498.     /**
  499.      * Removes from this list all of the elements whose index is between
  500.      * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
  501.      * Shifts any succeeding elements to the left (reduces their index).
  502.      * This call shortens the list by {@code (toIndex - fromIndex)} elements.
  503.      * (If {@code toIndex==fromIndex}, this operation has no effect.)
  504.      *
  505.      * @throws IndexOutOfBoundsException if {@code fromIndex} or
  506.      *         {@code toIndex} is out of range
  507.      *         ({@code fromIndex < 0 ||
  508.      *          fromIndex >= size() ||
  509.      *          toIndex > size() ||
  510.      *          toIndex < fromIndex})
  511.      */
  512.     protected void removeRange(int fromIndex, int toIndex) {
  513.         modCount++;
  514.         int numMoved = size - toIndex;
  515.         System.arraycopy(elementData, toIndex, elementData, fromIndex,
  516.                          numMoved);
  518.         // clear to let GC do its work
  519.         int newSize = size - (toIndex-fromIndex);
  520.         for (int i = newSize; i < size; i++) {
  521.             elementData[i] = null;
  522.         }
  523.         size = newSize;
  524.     }
  526.     /**
  527.      * Checks if the given index is in range.  If not, throws an appropriate
  528.      * runtime exception.  This method does *not* check if the index is
  529.      * negative: It is always used immediately prior to an array access,
  530.      * which throws an ArrayIndexOutOfBoundsException if index is negative.
  531.      */
  532.     private void rangeCheck(int index) {
  533.         if (index >= size)
  534.             throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
  535.     }
  537.     /**
  538.      * A version of rangeCheck used by add and addAll.
  539.      */
  540.     private void rangeCheckForAdd(int index) {
  541.         if (index > size || index < 0)
  542.             throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
  543.     }
  545.     /**
  546.      * Constructs an IndexOutOfBoundsException detail message.
  547.      * Of the many possible refactorings of the error handling code,
  548.      * this "outlining" performs best with both server and client VMs.
  549.      */
  550.     private String outOfBoundsMsg(int index) {
  551.         return "Index: "+index+", Size: "+size;
  552.     }
  554.     /**
  555.      * Removes from this list all of its elements that are contained in the
  556.      * specified collection.
  557.      *
  558.      * @param c collection containing elements to be removed from this list
  559.      * @return {@code true} if this list changed as a result of the call
  560.      * @throws ClassCastException if the class of an element of this list
  561.      *         is incompatible with the specified collection
  562.      * (<a href="Collection.html#optional-restrictions">optional</a>)
  563.      * @throws NullPointerException if this list contains a null element and the
  564.      *         specified collection does not permit null elements
  565.      * (<a href="Collection.html#optional-restrictions">optional</a>),
  566.      *         or if the specified collection is null
  567.      * @see Collection#contains(Object)
  568.      */
  569.     public boolean removeAll(Collection<?> c) {
  570.         return batchRemove(c, false);
  571.     }
  573.     /**
  574.      * Retains only the elements in this list that are contained in the
  575.      * specified collection.  In other words, removes from this list all
  576.      * of its elements that are not contained in the specified collection.
  577.      *
  578.      * @param c collection containing elements to be retained in this list
  579.      * @return {@code true} if this list changed as a result of the call
  580.      * @throws ClassCastException if the class of an element of this list
  581.      *         is incompatible with the specified collection
  582.      * (<a href="Collection.html#optional-restrictions">optional</a>)
  583.      * @throws NullPointerException if this list contains a null element and the
  584.      *         specified collection does not permit null elements
  585.      * (<a href="Collection.html#optional-restrictions">optional</a>),
  586.      *         or if the specified collection is null
  587.      * @see Collection#contains(Object)
  588.      */
  589.     public boolean retainAll(Collection<?> c) {
  590.         return batchRemove(c, true);
  591.     }
  593.     private boolean batchRemove(Collection<?> c, boolean complement) {
  594.         final Object[] elementData = this.elementData;
  595.         int r = 0, w = 0;
  596.         boolean modified = false;
  597.         try {
  598.             for (; r < size; r++)
  599.                 if (c.contains(elementData[r]) == complement)
  600.                     elementData[w++] = elementData[r];
  601.         } finally {
  602.             // Preserve behavioral compatibility with AbstractCollection,
  603.             // even if c.contains() throws.
  604.             if (r != size) {
  605.                 System.arraycopy(elementData, r,
  606.                                  elementData, w,
  607.                                  size - r);
  608.                 w += size - r;
  609.             }
  610.             if (w != size) {
  611.                 // clear to let GC do its work
  612.                 for (int i = w; i < size; i++)
  613.                     elementData[i] = null;
  614.                 modCount += size - w;
  615.                 size = w;
  616.                 modified = true;
  617.             }
  618.         }
  619.         return modified;
  620.     }
  622.     /**
  623.      * Save the state of the <tt>ArrayList</tt> instance to a stream (that
  624.      * is, serialize it).
  625.      *
  626.      * @serialData The length of the array backing the <tt>ArrayList</tt>
  627.      *             instance is emitted (int), followed by all of its elements
  628.      *             (each an <tt>Object</tt>) in the proper order.
  629.      */
  630.     private void writeObject(java.io.ObjectOutputStream s)
  631.         throws java.io.IOException{
  632.         // Write out element count, and any hidden stuff
  633.         int expectedModCount = modCount;
  634.         s.defaultWriteObject();
  636.         // Write out size as capacity for behavioural compatibility with clone()
  637.         s.writeInt(size);
  639.         // Write out all elements in the proper order.
  640.         for (int i=0; i<size; i++) {
  641.             s.writeObject(elementData[i]);
  642.         }
  644.         if (modCount != expectedModCount) {
  645.             throw new ConcurrentModificationException();
  646.         }
  647.     }
  649.     /**
  650.      * Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
  651.      * deserialize it).
  652.      */
  653.     private void readObject(java.io.ObjectInputStream s)
  654.         throws java.io.IOException, ClassNotFoundException {
  655.         elementData = EMPTY_ELEMENTDATA;
  657.         // Read in size, and any hidden stuff
  658.         s.defaultReadObject();
  660.         // Read in capacity
  661.         s.readInt(); // ignored
  663.         if (size > 0) {
  664.             // be like clone(), allocate array based upon size not capacity
  665.             ensureCapacityInternal(size);
  667.             Object[] a = elementData;
  668.             // Read in all elements in the proper order.
  669.             for (int i=0; i<size; i++) {
  670.                 a[i] = s.readObject();
  671.             }
  672.         }
  673.     }
  675.     /**
  676.      * Returns a list iterator over the elements in this list (in proper
  677.      * sequence), starting at the specified position in the list.
  678.      * The specified index indicates the first element that would be
  679.      * returned by an initial call to {@link ListIterator#next next}.
  680.      * An initial call to {@link ListIterator#previous previous} would
  681.      * return the element with the specified index minus one.
  682.      *
  683.      * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
  684.      *
  685.      * @throws IndexOutOfBoundsException {@inheritDoc}
  686.      */
  687.     public ListIterator<E> listIterator(int index) {
  688.         if (index < 0 || index > size)
  689.             throw new IndexOutOfBoundsException("Index: "+index);
  690.         return new ListItr(index);
  691.     }
  693.     /**
  694.      * Returns a list iterator over the elements in this list (in proper
  695.      * sequence).
  696.      *
  697.      * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
  698.      *
  699.      * @see #listIterator(int)
  700.      */
  701.     public ListIterator<E> listIterator() {
  702.         return new ListItr(0);
  703.     }
  705.     /**
  706.      * Returns an iterator over the elements in this list in proper sequence.
  707.      *
  708.      * <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
  709.      *
  710.      * @return an iterator over the elements in this list in proper sequence
  711.      */
  712.     public Iterator<E> iterator() {
  713.         return new Itr();
  714.     }
  716.     /**
  717.      * An optimized version of AbstractList.Itr
  718.      */
  719.     private class Itr implements Iterator<E> {
  720.         int cursor;       // index of next element to return
  721.         int lastRet = -1; // index of last element returned; -1 if no such
  722.         int expectedModCount = modCount;
  724.         public boolean hasNext() {
  725.             return cursor != size;
  726.         }
  728.         @SuppressWarnings("unchecked")
  729.         public E next() {
  730.             checkForComodification();
  731.             int i = cursor;
  732.             if (i >= size)
  733.                 throw new NoSuchElementException();
  734.             Object[] elementData = ArrayList.this.elementData;
  735.             if (i >= elementData.length)
  736.                 throw new ConcurrentModificationException();
  737.             cursor = i + 1;
  738.             return (E) elementData[lastRet = i];
  739.         }
  741.         public void remove() {
  742.             if (lastRet < 0)
  743.                 throw new IllegalStateException();
  744.             checkForComodification();
  746.             try {
  747.                 ArrayList.this.remove(lastRet);
  748.                 cursor = lastRet;
  749.                 lastRet = -1;
  750.                 expectedModCount = modCount;
  751.             } catch (IndexOutOfBoundsException ex) {
  752.                 throw new ConcurrentModificationException();
  753.             }
  754.         }
  756.         final void checkForComodification() {
  757.             if (modCount != expectedModCount)
  758.                 throw new ConcurrentModificationException();
  759.         }
  760.     }
  762.     /**
  763.      * An optimized version of AbstractList.ListItr
  764.      */
  765.     private class ListItr extends Itr implements ListIterator<E> {
  766.         ListItr(int index) {
  767.             super();
  768.             cursor = index;
  769.         }
  771.         public boolean hasPrevious() {
  772.             return cursor != 0;
  773.         }
  775.         public int nextIndex() {
  776.             return cursor;
  777.         }
  779.         public int previousIndex() {
  780.             return cursor - 1;
  781.         }
  783.         @SuppressWarnings("unchecked")
  784.         public E previous() {
  785.             checkForComodification();
  786.             int i = cursor - 1;
  787.             if (i < 0)
  788.                 throw new NoSuchElementException();
  789.             Object[] elementData = ArrayList.this.elementData;
  790.             if (i >= elementData.length)
  791.                 throw new ConcurrentModificationException();
  792.             cursor = i;
  793.             return (E) elementData[lastRet = i];
  794.         }
  796.         public void set(E e) {
  797.             if (lastRet < 0)
  798.                 throw new IllegalStateException();
  799.             checkForComodification();
  801.             try {
  802.                 ArrayList.this.set(lastRet, e);
  803.             } catch (IndexOutOfBoundsException ex) {
  804.                 throw new ConcurrentModificationException();
  805.             }
  806.         }
  808.         public void add(E e) {
  809.             checkForComodification();
  811.             try {
  812.                 int i = cursor;
  813.                 ArrayList.this.add(i, e);
  814.                 cursor = i + 1;
  815.                 lastRet = -1;
  816.                 expectedModCount = modCount;
  817.             } catch (IndexOutOfBoundsException ex) {
  818.                 throw new ConcurrentModificationException();
  819.             }
  820.         }
  821.     }
  823.     /**
  824.      * Returns a view of the portion of this list between the specified
  825.      * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.  (If
  826.      * {@code fromIndex} and {@code toIndex} are equal, the returned list is
  827.      * empty.)  The returned list is backed by this list, so non-structural
  828.      * changes in the returned list are reflected in this list, and vice-versa.
  829.      * The returned list supports all of the optional list operations.
  830.      *
  831.      * <p>This method eliminates the need for explicit range operations (of
  832.      * the sort that commonly exist for arrays).  Any operation that expects
  833.      * a list can be used as a range operation by passing a subList view
  834.      * instead of a whole list.  For example, the following idiom
  835.      * removes a range of elements from a list:
  836.      * <pre>
  837.      *      list.subList(from, to).clear();
  838.      * </pre>
  839.      * Similar idioms may be constructed for {@link #indexOf(Object)} and
  840.      * {@link #lastIndexOf(Object)}, and all of the algorithms in the
  841.      * {@link Collections} class can be applied to a subList.
  842.      *
  843.      * <p>The semantics of the list returned by this method become undefined if
  844.      * the backing list (i.e., this list) is <i>structurally modified</i> in
  845.      * any way other than via the returned list.  (Structural modifications are
  846.      * those that change the size of this list, or otherwise perturb it in such
  847.      * a fashion that iterations in progress may yield incorrect results.)
  848.      *
  849.      * @throws IndexOutOfBoundsException {@inheritDoc}
  850.      * @throws IllegalArgumentException {@inheritDoc}
  851.      */
  852.     public List<E> subList(int fromIndex, int toIndex) {
  853.         subListRangeCheck(fromIndex, toIndex, size);
  854.         return new SubList(this, 0, fromIndex, toIndex);
  855.     }
  857.     static void subListRangeCheck(int fromIndex, int toIndex, int size) {
  858.         if (fromIndex < 0)
  859.             throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
  860.         if (toIndex > size)
  861.             throw new IndexOutOfBoundsException("toIndex = " + toIndex);
  862.         if (fromIndex > toIndex)
  863.             throw new IllegalArgumentException("fromIndex(" + fromIndex +
  864.                                                ") > toIndex(" + toIndex + ")");
  865.     }
  867.     private class SubList extends AbstractList<E> implements RandomAccess {
  868.         private final AbstractList<E> parent;
  869.         private final int parentOffset;
  870.         private final int offset;
  871.         int size;
  873.         SubList(AbstractList<E> parent,
  874.                 int offset, int fromIndex, int toIndex) {
  875.             this.parent = parent;
  876.             this.parentOffset = fromIndex;
  877.             this.offset = offset + fromIndex;
  878.             this.size = toIndex - fromIndex;
  879.             this.modCount = ArrayList.this.modCount;
  880.         }
  882.         public E set(int index, E e) {
  883.             rangeCheck(index);
  884.             checkForComodification();
  885.             E oldValue = ArrayList.this.elementData(offset + index);
  886.             ArrayList.this.elementData[offset + index] = e;
  887.             return oldValue;
  888.         }
  890.         public E get(int index) {
  891.             rangeCheck(index);
  892.             checkForComodification();
  893.             return ArrayList.this.elementData(offset + index);
  894.         }
  896.         public int size() {
  897.             checkForComodification();
  898.             return this.size;
  899.         }
  901.         public void add(int index, E e) {
  902.             rangeCheckForAdd(index);
  903.             checkForComodification();
  904.             parent.add(parentOffset + index, e);
  905.             this.modCount = parent.modCount;
  906.             this.size++;
  907.         }
  909.         public E remove(int index) {
  910.             rangeCheck(index);
  911.             checkForComodification();
  912.             E result = parent.remove(parentOffset + index);
  913.             this.modCount = parent.modCount;
  914.             this.size--;
  915.             return result;
  916.         }
  918.         protected void removeRange(int fromIndex, int toIndex) {
  919.             checkForComodification();
  920.             parent.removeRange(parentOffset + fromIndex,
  921.                                parentOffset + toIndex);
  922.             this.modCount = parent.modCount;
  923.             this.size -= toIndex - fromIndex;
  924.         }
  926.         public boolean addAll(Collection<? extends E> c) {
  927.             return addAll(this.size, c);
  928.         }
  930.         public boolean addAll(int index, Collection<? extends E> c) {
  931.             rangeCheckForAdd(index);
  932.             int cSize = c.size();
  933.             if (cSize==0)
  934.                 return false;
  936.             checkForComodification();
  937.             parent.addAll(parentOffset + index, c);
  938.             this.modCount = parent.modCount;
  939.             this.size += cSize;
  940.             return true;
  941.         }
  943.         public Iterator<E> iterator() {
  944.             return listIterator();
  945.         }
  947.         public ListIterator<E> listIterator(final int index) {
  948.             checkForComodification();
  949.             rangeCheckForAdd(index);
  950.             final int offset = this.offset;
  952.             return new ListIterator<E>() {
  953.                 int cursor = index;
  954.                 int lastRet = -1;
  955.                 int expectedModCount = ArrayList.this.modCount;
  957.                 public boolean hasNext() {
  958.                     return cursor != SubList.this.size;
  959.                 }
  961.                 @SuppressWarnings("unchecked")
  962.                 public E next() {
  963.                     checkForComodification();
  964.                     int i = cursor;
  965.                     if (i >= SubList.this.size)
  966.                         throw new NoSuchElementException();
  967.                     Object[] elementData = ArrayList.this.elementData;
  968.                     if (offset + i >= elementData.length)
  969.                         throw new ConcurrentModificationException();
  970.                     cursor = i + 1;
  971.                     return (E) elementData[offset + (lastRet = i)];
  972.                 }
  974.                 public boolean hasPrevious() {
  975.                     return cursor != 0;
  976.                 }
  978.                 @SuppressWarnings("unchecked")
  979.                 public E previous() {
  980.                     checkForComodification();
  981.                     int i = cursor - 1;
  982.                     if (i < 0)
  983.                         throw new NoSuchElementException();
  984.                     Object[] elementData = ArrayList.this.elementData;
  985.                     if (offset + i >= elementData.length)
  986.                         throw new ConcurrentModificationException();
  987.                     cursor = i;
  988.                     return (E) elementData[offset + (lastRet = i)];
  989.                 }
  991.                 public int nextIndex() {
  992.                     return cursor;
  993.                 }
  995.                 public int previousIndex() {
  996.                     return cursor - 1;
  997.                 }
  999.                 public void remove() {
  1000.                     if (lastRet < 0)
  1001.                         throw new IllegalStateException();
  1002.                     checkForComodification();
  1004.                     try {
  1005.                         SubList.this.remove(lastRet);
  1006.                         cursor = lastRet;
  1007.                         lastRet = -1;
  1008.                         expectedModCount = ArrayList.this.modCount;
  1009.                     } catch (IndexOutOfBoundsException ex) {
  1010.                         throw new ConcurrentModificationException();
  1011.                     }
  1012.                 }
  1014.                 public void set(E e) {
  1015.                     if (lastRet < 0)
  1016.                         throw new IllegalStateException();
  1017.                     checkForComodification();
  1019.                     try {
  1020.                         ArrayList.this.set(offset + lastRet, e);
  1021.                     } catch (IndexOutOfBoundsException ex) {
  1022.                         throw new ConcurrentModificationException();
  1023.                     }
  1024.                 }
  1026.                 public void add(E e) {
  1027.                     checkForComodification();
  1029.                     try {
  1030.                         int i = cursor;
  1031.                         SubList.this.add(i, e);
  1032.                         cursor = i + 1;
  1033.                         lastRet = -1;
  1034.                         expectedModCount = ArrayList.this.modCount;
  1035.                     } catch (IndexOutOfBoundsException ex) {
  1036.                         throw new ConcurrentModificationException();
  1037.                     }
  1038.                 }
  1040.                 final void checkForComodification() {
  1041.                     if (expectedModCount != ArrayList.this.modCount)
  1042.                         throw new ConcurrentModificationException();
  1043.                 }
  1044.             };
  1045.         }
  1047.         public List<E> subList(int fromIndex, int toIndex) {
  1048.             subListRangeCheck(fromIndex, toIndex, size);
  1049.             return new SubList(this, offset, fromIndex, toIndex);
  1050.         }
  1052.         private void rangeCheck(int index) {
  1053.             if (index < 0 || index >= this.size)
  1054.                 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
  1055.         }
  1057.         private void rangeCheckForAdd(int index) {
  1058.             if (index < 0 || index > this.size)
  1059.                 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
  1060.         }
  1062.         private String outOfBoundsMsg(int index) {
  1063.             return "Index: "+index+", Size: "+this.size;
  1064.         }
  1066.         private void checkForComodification() {
  1067.             if (ArrayList.this.modCount != this.modCount)
  1068.                 throw new ConcurrentModificationException();
  1069.         }
  1070.     }
  1071. }
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