Java中ArrayList源码

/* * @(#)ArrayList.java1.56 06/04/21 * * Copyright 2006 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */package java.util;/** * Resizable-array implementation of the <tt>List</tt> interface.  Implements * all optional list operations, and permits all elements, including * <tt>null</tt>.  In addition to implementing the <tt>List</tt> interface, * this class provides methods to manipulate the size of the array that is * used internally to store the list.  (This class is roughly equivalent to * <tt>Vector</tt>, except that it is unsynchronized.)<p> * * The <tt>size</tt>, <tt>isEmpty</tt>, <tt>get</tt>, <tt>set</tt>, * <tt>iterator</tt>, and <tt>listIterator</tt> operations run in constant * time.  The <tt>add</tt> operation runs in <i>amortized constant time</i>, * that is, adding n elements requires O(n) time.  All of the other operations * run in linear time (roughly speaking).  The constant factor is low compared * to that for the <tt>LinkedList</tt> implementation.<p> * * Each <tt>ArrayList</tt> instance has a <i>capacity</i>.  The capacity is * the size of the array used to store the elements in the list.  It is always * at least as large as the list size.  As elements are added to an ArrayList, * its capacity grows automatically.  The details of the growth policy are not * specified beyond the fact that adding an element has constant amortized * time cost.<p> * * An application can increase the capacity of an <tt>ArrayList</tt> instance * before adding a large number of elements using the <tt>ensureCapacity</tt> * operation.  This may reduce the amount of incremental reallocation. * * <p><strong>Note that this implementation is not synchronized.</strong> * If multiple threads access an <tt>ArrayList</tt> instance concurrently, * and at least one of the threads modifies the list structurally, it * <i>must</i> be synchronized externally.  (A structural modification is * any operation that adds or deletes one or more elements, or explicitly * resizes the backing array; merely setting the value of an element is not * a structural modification.)  This is typically accomplished by * synchronizing on some object that naturally encapsulates the list. * * If no such object exists, the list should be "wrapped" using the * {@link Collections#synchronizedList Collections.synchronizedList} * method.  This is best done at creation time, to prevent accidental * unsynchronized access to the list:<pre> *   List list = Collections.synchronizedList(new ArrayList(...));</pre> * * <p>The iterators returned by this class's <tt>iterator</tt> and * <tt>listIterator</tt> methods are <i>fail-fast</i>: if the list is * structurally modified at any time after the iterator is created, in any way * except through the iterator's own <tt>remove</tt> or <tt>add</tt> methods, * the iterator will throw a {@link ConcurrentModificationException}.  Thus, in * the face of concurrent modification, the iterator fails quickly and cleanly, * rather than risking arbitrary, non-deterministic behavior at an undetermined * time in the future.<p> * * Note that the fail-fast behavior of an iterator cannot be guaranteed * as it is, generally speaking, impossible to make any hard guarantees in the * presence of unsynchronized concurrent modification.  Fail-fast iterators * throw <tt>ConcurrentModificationException</tt> on a best-effort basis. * Therefore, it would be wrong to write a program that depended on this * exception for its correctness: <i>the fail-fast behavior of iterators * should be used only to detect bugs.</i><p> * * This class is a member of the * <a href="{@docRoot}/../technotes/guides/collections/index.html"> * Java Collections Framework</a>. * * @author  Josh Bloch * @author  Neal Gafter * @version 1.56, 04/21/06 * @see    Collection * @see    List * @see    LinkedList * @see    Vector * @since   1.2 */public class ArrayList<E> extends AbstractList<E>        implements List<E>, RandomAccess, Cloneable, java.io.Serializable{    private static final long serialVersionUID = 8683452581122892189L;    /**     * The array buffer into which the elements of the ArrayList are stored.     * The capacity of the ArrayList is the length of this array buffer.     */    private transient Object[] elementData;    /**     * The size of the ArrayList (the number of elements it contains).     *     * @serial     */    private int size;    /**     * Constructs an empty list with the specified initial capacity.     *     * @param   initialCapacity   the initial capacity of the list     * @exception IllegalArgumentException if the specified initial capacity     *            is negative     */    public ArrayList(int initialCapacity) {super();        if (initialCapacity < 0)            throw new IllegalArgumentException("Illegal Capacity: "+                                               initialCapacity);this.elementData = new Object[initialCapacity];    }    /**     * Constructs an empty list with an initial capacity of ten.     */    public ArrayList() {this(10);    }    /**     * Constructs a list containing the elements of the specified     * collection, in the order they are returned by the collection's     * iterator.     *     * @param c the collection whose elements are to be placed into this list     * @throws NullPointerException if the specified collection is null     */    public ArrayList(Collection<? extends E> c) {elementData = c.toArray();size = elementData.length;// c.toArray might (incorrectly) not return Object[] (see 6260652)if (elementData.getClass() != Object[].class)    elementData = Arrays.copyOf(elementData, size, Object[].class);    }    /**     * Trims the capacity of this <tt>ArrayList</tt> instance to be the     * list's current size.  An application can use this operation to minimize     * the storage of an <tt>ArrayList</tt> instance.     */    public void trimToSize() {modCount++;int oldCapacity = elementData.length;if (size < oldCapacity) {            elementData = Arrays.copyOf(elementData, size);}    }    /**     * Increases the capacity of this <tt>ArrayList</tt> instance, if     * necessary, to ensure that it can hold at least the number of elements     * specified by the minimum capacity argument.     *     * @param   minCapacity   the desired minimum capacity     */    public void ensureCapacity(int minCapacity) {modCount++;int oldCapacity = elementData.length;if (minCapacity > oldCapacity) {    Object oldData[] = elementData;    int newCapacity = (oldCapacity * 3)/2 + 1;        if (newCapacity < minCapacity)newCapacity = minCapacity;            // minCapacity is usually close to size, so this is a win:            elementData = Arrays.copyOf(elementData, newCapacity);}    }    /**     * Returns the number of elements in this list.     *     * @return the number of elements in this list     */    public int size() {return size;    }    /**     * Returns <tt>true</tt> if this list contains no elements.     *     * @return <tt>true</tt> if this list contains no elements     */    public boolean isEmpty() {return size == 0;    }    /**     * 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     */    public boolean contains(Object o) {return indexOf(o) >= 0;    }    /**     * 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.     */    public int indexOf(Object o) {if (o == null) {    for (int i = 0; i < size; i++)if (elementData[i]==null)    return i;} else {    for (int i = 0; i < size; i++)if (o.equals(elementData[i]))    return i;}return -1;    }    /**     * 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.     */    public int lastIndexOf(Object o) {if (o == null) {    for (int i = size-1; i >= 0; i--)if (elementData[i]==null)    return i;} else {    for (int i = size-1; i >= 0; i--)if (o.equals(elementData[i]))    return i;}return -1;    }    /**     * Returns a shallow copy of this <tt>ArrayList</tt> instance.  (The     * elements themselves are not copied.)     *     * @return a clone of this <tt>ArrayList</tt> instance     */    public Object clone() {try {    ArrayList<E> v = (ArrayList<E>) super.clone();    v.elementData = Arrays.copyOf(elementData, size);    v.modCount = 0;    return v;} catch (CloneNotSupportedException e) {    // this shouldn't happen, since we are Cloneable    throw new InternalError();}    }    /**     * 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).  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     */    public Object[] toArray() {        return Arrays.copyOf(elementData, size);    }    /**     * 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 collection 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.)     *     * @param a the array into which the elements of the 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 the 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     */    public <T> T[] toArray(T[] a) {        if (a.length < size)            // Make a new array of a's runtime type, but my contents:            return (T[]) Arrays.copyOf(elementData, size, a.getClass());System.arraycopy(elementData, 0, a, 0, size);        if (a.length > size)            a[size] = null;        return a;    }    // 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 {@inheritDoc}     */    public E get(int index) {RangeCheck(index);return (E) elementData[index];    }    /**     * Replaces the element at the specified position in this list with     * the specified element.     *     * @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 IndexOutOfBoundsException {@inheritDoc}     */    public E set(int index, E element) {RangeCheck(index);E oldValue = (E) elementData[index];elementData[index] = element;return oldValue;    }    /**     * Appends the specified element to the end of this list.     *     * @param e element to be appended to this list     * @return <tt>true</tt> (as specified by {@link Collection#add})     */    public boolean add(E e) {ensureCapacity(size + 1);  // Increments modCount!!elementData[size++] = e;return true;    }    /**     * Inserts the specified element at the specified position in this     * list. 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 IndexOutOfBoundsException {@inheritDoc}     */    public void add(int index, E element) {if (index > size || index < 0)    throw new IndexOutOfBoundsException("Index: "+index+", Size: "+size);ensureCapacity(size+1);  // Increments modCount!!System.arraycopy(elementData, index, elementData, index + 1, size - index);elementData[index] = element;size++;    }    /**     * Removes the element at the specified position in this list.     * Shifts any subsequent elements to the left (subtracts one from their     * indices).     *     * @param index the index of the element to be removed     * @return the element that was removed from the list     * @throws IndexOutOfBoundsException {@inheritDoc}     */    public E remove(int index) {RangeCheck(index);modCount++;E oldValue = (E) elementData[index];int numMoved = size - index - 1;if (numMoved > 0)    System.arraycopy(elementData, index+1, elementData, index,     numMoved);elementData[--size] = null; // Let gc do its workreturn oldValue;    }    /**     * Removes the first occurrence of the specified element from this list,     * if it is present.  If the 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     */    public boolean remove(Object o) {if (o == null) {            for (int index = 0; index < size; index++)if (elementData[index] == null) {    fastRemove(index);    return true;}} else {    for (int index = 0; index < size; index++)if (o.equals(elementData[index])) {    fastRemove(index);    return true;}        }return false;    }    /*     * Private remove method that skips bounds checking and does not     * return the value removed.     */    private void fastRemove(int index) {        modCount++;        int numMoved = size - index - 1;        if (numMoved > 0)            System.arraycopy(elementData, index+1, elementData, index,                             numMoved);        elementData[--size] = null; // Let gc do its work    }    /**     * Removes all of the elements from this list.  The list will     * be empty after this call returns.     */    public void clear() {modCount++;// Let gc do its workfor (int i = 0; i < size; i++)    elementData[i] = null;size = 0;    }    /**     * 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.  The behavior of this operation is     * undefined if the specified collection is modified while the operation     * is in progress.  (This implies that the behavior of this call is     * undefined if the specified collection is this list, and this     * list is 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 NullPointerException if the specified collection is null     */    public boolean addAll(Collection<? extends E> c) {Object[] a = c.toArray();        int numNew = a.length;ensureCapacity(size + numNew);  // Increments modCount        System.arraycopy(a, 0, elementData, size, numNew);        size += numNew;return numNew != 0;    }    /**     * Inserts all of the elements in the specified collection into this     * list, starting at the specified position.  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 the list in the order that they are returned by the     * specified collection's iterator.     *     * @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 IndexOutOfBoundsException {@inheritDoc}     * @throws NullPointerException if the specified collection is null     */    public boolean addAll(int index, Collection<? extends E> c) {if (index > size || index < 0)    throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size);Object[] a = c.toArray();int numNew = a.length;ensureCapacity(size + numNew);  // Increments modCountint numMoved = size - index;if (numMoved > 0)    System.arraycopy(elementData, index, elementData, index + numNew,     numMoved);        System.arraycopy(a, 0, elementData, index, numNew);size += numNew;return numNew != 0;    }    /**     * Removes from this list all of the elements whose index is between     * <tt>fromIndex</tt>, inclusive, and <tt>toIndex</tt>, exclusive.     * Shifts any succeeding elements to the left (reduces their index).     * This call shortens the list by <tt>(toIndex - fromIndex)</tt> elements.     * (If <tt>toIndex==fromIndex</tt>, this operation has no effect.)     *     * @param fromIndex index of first element to be removed     * @param toIndex index after last element to be removed     * @throws IndexOutOfBoundsException if fromIndex or toIndex out of     *              range (fromIndex < 0 || fromIndex >= size() || toIndex     *              > size() || toIndex < fromIndex)     */    protected void removeRange(int fromIndex, int toIndex) {modCount++;int numMoved = size - toIndex;        System.arraycopy(elementData, toIndex, elementData, fromIndex,                         numMoved);// Let gc do its workint newSize = size - (toIndex-fromIndex);while (size != newSize)    elementData[--size] = null;    }    /**     * Checks if the given index is in range.  If not, throws an appropriate     * runtime exception.  This method does *not* check if the index is     * negative: It is always used immediately prior to an array access,     * which throws an ArrayIndexOutOfBoundsException if index is negative.     */    private void RangeCheck(int index) {if (index >= size)    throw new IndexOutOfBoundsException("Index: "+index+", Size: "+size);    }    /**     * Save the state of the <tt>ArrayList</tt> instance to a stream (that     * is, serialize it).     *     * @serialData The length of the array backing the <tt>ArrayList</tt>     *             instance is emitted (int), followed by all of its elements     *             (each an <tt>Object</tt>) in the proper order.     */    private void writeObject(java.io.ObjectOutputStream s)        throws java.io.IOException{// Write out element count, and any hidden stuffint expectedModCount = modCount;s.defaultWriteObject();        // Write out array length        s.writeInt(elementData.length);// Write out all elements in the proper order.for (int i=0; i<size; i++)            s.writeObject(elementData[i]);if (modCount != expectedModCount) {            throw new ConcurrentModificationException();        }    }    /**     * Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,     * deserialize it).     */    private void readObject(java.io.ObjectInputStream s)        throws java.io.IOException, ClassNotFoundException {// Read in size, and any hidden stuffs.defaultReadObject();        // Read in array length and allocate array        int arrayLength = s.readInt();        Object[] a = elementData = new Object[arrayLength];// Read in all elements in the proper order.for (int i=0; i<size; i++)            a[i] = s.readObject();    }}