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3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4    *
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13   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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25  
26  package java.util;
27  
28  import java.util.function.Consumer;
29  import java.util.function.Predicate;
30  import java.util.function.UnaryOperator;
31  
32  /**
33   * The {@code Vector} class implements a growable array of
34   * objects. Like an array, it contains components that can be
35   * accessed using an integer index. However, the size of a
36   * {@code Vector} can grow or shrink as needed to accommodate
37   * adding and removing items after the {@code Vector} has been created.
38   *
39   * <p>Each vector tries to optimize storage management by maintaining a
40   * {@code capacity} and a {@code capacityIncrement}. The
41   * {@code capacity} is always at least as large as the vector
42   * size; it is usually larger because as components are added to the
43   * vector, the vector's storage increases in chunks the size of
44   * {@code capacityIncrement}. An application can increase the
45   * capacity of a vector before inserting a large number of
46   * components; this reduces the amount of incremental reallocation.
47   *
48   * <p><a name="fail-fast">
49   * The iterators returned by this class's {@link #iterator() iterator} and
50   * {@link #listIterator(int) listIterator} methods are <em>fail-fast</em></a>:
51   * if the vector is structurally modified at any time after the iterator is
52   * created, in any way except through the iterator's own
53   * {@link ListIterator#remove() remove} or
54   * {@link ListIterator#add(Object) add} methods, the iterator will throw a
55   * {@link ConcurrentModificationException}.  Thus, in the face of
56   * concurrent modification, the iterator fails quickly and cleanly, rather
57   * than risking arbitrary, non-deterministic behavior at an undetermined
58   * time in the future.  The {@link Enumeration Enumerations} returned by
59   * the {@link #elements() elements} method are <em>not</em> fail-fast.
60   *
61   * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
62   * as it is, generally speaking, impossible to make any hard guarantees in the
63   * presence of unsynchronized concurrent modification.  Fail-fast iterators
64   * throw {@code ConcurrentModificationException} on a best-effort basis.
65   * Therefore, it would be wrong to write a program that depended on this
66   * exception for its correctness:  <i>the fail-fast behavior of iterators
67   * should be used only to detect bugs.</i>
68   *
69   * <p>As of the Java 2 platform v1.2, this class was retrofitted to
70   * implement the {@link List} interface, making it a member of the
71   * <a href="{@docRoot}/../technotes/guides/collections/index.html">
72   * Java Collections Framework</a>.  Unlike the new collection
73   * implementations, {@code Vector} is synchronized.  If a thread-safe
74   * implementation is not needed, it is recommended to use {@link
75   * ArrayList} in place of {@code Vector}.
76   *
77   * @author  Lee Boynton
78   * @author  Jonathan Payne
79   * @see Collection
80   * @see LinkedList
81   * @since   JDK1.0
82   */
83  public class Vector<E>
84      extends AbstractList<E>
85      implements List<E>, RandomAccess, Cloneable, java.io.Serializable
86  {
87      /**
88       * The array buffer into which the components of the vector are
89       * stored. The capacity of the vector is the length of this array buffer,
90       * and is at least large enough to contain all the vector's elements.
91       *
92       * <p>Any array elements following the last element in the Vector are null.
93       *
94       * @serial
95       */
96      protected Object[] elementData;
97  
98      /**
99       * The number of valid components in this {@code Vector} object.
100      * Components {@code elementData[0]} through
101      * {@code elementData[elementCount-1]} are the actual items.
102      *
103      * @serial
104      */
105     protected int elementCount;
106 
107     /**
108      * The amount by which the capacity of the vector is automatically
109      * incremented when its size becomes greater than its capacity.  If
110      * the capacity increment is less than or equal to zero, the capacity
111      * of the vector is doubled each time it needs to grow.
112      *
113      * @serial
114      */
115     protected int capacityIncrement;
116 
117     /** use serialVersionUID from JDK 1.0.2 for interoperability */
118     private static final long serialVersionUID = -2767605614048989439L;
119 
120     /**
121      * Constructs an empty vector with the specified initial capacity and
122      * capacity increment.
123      *
124      * @param   initialCapacity     the initial capacity of the vector
125      * @param   capacityIncrement   the amount by which the capacity is
126      *                              increased when the vector overflows
127      * @throws IllegalArgumentException if the specified initial capacity
128      *         is negative
129      */
130     public Vector(int initialCapacity, int capacityIncrement) {
131         super();
132         if (initialCapacity < 0)
133             throw new IllegalArgumentException("Illegal Capacity: "+
134                                                initialCapacity);
135         this.elementData = new Object[initialCapacity];
136         this.capacityIncrement = capacityIncrement;
137     }
138 
139     /**
140      * Constructs an empty vector with the specified initial capacity and
141      * with its capacity increment equal to zero.
142      *
143      * @param   initialCapacity   the initial capacity of the vector
144      * @throws IllegalArgumentException if the specified initial capacity
145      *         is negative
146      */
147     public Vector(int initialCapacity) {
148         this(initialCapacity, 0);
149     }
150 
151     /**
152      * Constructs an empty vector so that its internal data array
153      * has size {@code 10} and its standard capacity increment is
154      * zero.
155      */
156     public Vector() {
157         this(10);
158     }
159 
160     /**
161      * Constructs a vector containing the elements of the specified
162      * collection, in the order they are returned by the collection's
163      * iterator.
164      *
165      * @param c the collection whose elements are to be placed into this
166      *       vector
167      * @throws NullPointerException if the specified collection is null
168      * @since   1.2
169      */
170     public Vector(Collection<? extends E> c) {
171         elementData = c.toArray();
172         elementCount = elementData.length;
173         // c.toArray might (incorrectly) not return Object[] (see 6260652)
174         if (elementData.getClass() != Object[].class)
175             elementData = Arrays.copyOf(elementData, elementCount, Object[].class);
176     }
177 
178     /**
179      * Copies the components of this vector into the specified array.
180      * The item at index {@code k} in this vector is copied into
181      * component {@code k} of {@code anArray}.
182      *
183      * @param  anArray the array into which the components get copied
184      * @throws NullPointerException if the given array is null
185      * @throws IndexOutOfBoundsException if the specified array is not
186      *         large enough to hold all the components of this vector
187      * @throws ArrayStoreException if a component of this vector is not of
188      *         a runtime type that can be stored in the specified array
189      * @see #toArray(Object[])
190      */
191     public synchronized void copyInto(Object[] anArray) {
192         System.arraycopy(elementData, 0, anArray, 0, elementCount);
193     }
194 
195     /**
196      * Trims the capacity of this vector to be the vector's current
197      * size. If the capacity of this vector is larger than its current
198      * size, then the capacity is changed to equal the size by replacing
199      * its internal data array, kept in the field {@code elementData},
200      * with a smaller one. An application can use this operation to
201      * minimize the storage of a vector.
202      */
203     public synchronized void trimToSize() {
204         modCount++;
205         int oldCapacity = elementData.length;
206         if (elementCount < oldCapacity) {
207             elementData = Arrays.copyOf(elementData, elementCount);
208         }
209     }
210 
211     /**
212      * Increases the capacity of this vector, if necessary, to ensure
213      * that it can hold at least the number of components specified by
214      * the minimum capacity argument.
215      *
216      * <p>If the current capacity of this vector is less than
217      * {@code minCapacity}, then its capacity is increased by replacing its
218      * internal data array, kept in the field {@code elementData}, with a
219      * larger one.  The size of the new data array will be the old size plus
220      * {@code capacityIncrement}, unless the value of
221      * {@code capacityIncrement} is less than or equal to zero, in which case
222      * the new capacity will be twice the old capacity; but if this new size
223      * is still smaller than {@code minCapacity}, then the new capacity will
224      * be {@code minCapacity}.
225      *
226      * @param minCapacity the desired minimum capacity
227      */
228     public synchronized void ensureCapacity(int minCapacity) {
229         if (minCapacity > 0) {
230             modCount++;
231             ensureCapacityHelper(minCapacity);
232         }
233     }
234 
235     /**
236      * This implements the unsynchronized semantics of ensureCapacity.
237      * Synchronized methods in this class can internally call this
238      * method for ensuring capacity without incurring the cost of an
239      * extra synchronization.
240      *
241      * @see #ensureCapacity(int)
242      */
243     private void ensureCapacityHelper(int minCapacity) {
244         // overflow-conscious code
245         if (minCapacity - elementData.length > 0)
246             grow(minCapacity);
247     }
248 
249     /**
250      * The maximum size of array to allocate.
251      * Some VMs reserve some header words in an array.
252      * Attempts to allocate larger arrays may result in
253      * OutOfMemoryError: Requested array size exceeds VM limit
254      */
255     private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
256 
257     private void grow(int minCapacity) {
258         // overflow-conscious code
259         int oldCapacity = elementData.length;
260         int newCapacity = oldCapacity + ((capacityIncrement > 0) ?
261                                          capacityIncrement : oldCapacity);
262         if (newCapacity - minCapacity < 0)
263             newCapacity = minCapacity;
264         if (newCapacity - MAX_ARRAY_SIZE > 0)
265             newCapacity = hugeCapacity(minCapacity);
266         elementData = Arrays.copyOf(elementData, newCapacity);
267     }
268 
269     private static int hugeCapacity(int minCapacity) {
270         if (minCapacity < 0) // overflow
271             throw new OutOfMemoryError();
272         return (minCapacity > MAX_ARRAY_SIZE) ?
273             Integer.MAX_VALUE :
274             MAX_ARRAY_SIZE;
275     }
276 
277     /**
278      * Sets the size of this vector. If the new size is greater than the
279      * current size, new {@code null} items are added to the end of
280      * the vector. If the new size is less than the current size, all
281      * components at index {@code newSize} and greater are discarded.
282      *
283      * @param  newSize   the new size of this vector
284      * @throws ArrayIndexOutOfBoundsException if the new size is negative
285      */
286     public synchronized void setSize(int newSize) {
287         modCount++;
288         if (newSize > elementCount) {
289             ensureCapacityHelper(newSize);
290         } else {
291             for (int i = newSize ; i < elementCount ; i++) {
292                 elementData[i] = null;
293             }
294         }
295         elementCount = newSize;
296     }
297 
298     /**
299      * Returns the current capacity of this vector.
300      *
301      * @return  the current capacity (the length of its internal
302      *          data array, kept in the field {@code elementData}
303      *          of this vector)
304      */
305     public synchronized int capacity() {
306         return elementData.length;
307     }
308 
309     /**
310      * Returns the number of components in this vector.
311      *
312      * @return  the number of components in this vector
313      */
314     public synchronized int size() {
315         return elementCount;
316     }
317 
318     /**
319      * Tests if this vector has no components.
320      *
321      * @return  {@code true} if and only if this vector has
322      *          no components, that is, its size is zero;
323      *          {@code false} otherwise.
324      */
325     public synchronized boolean isEmpty() {
326         return elementCount == 0;
327     }
328 
329     /**
330      * Returns an enumeration of the components of this vector. The
331      * returned {@code Enumeration} object will generate all items in
332      * this vector. The first item generated is the item at index {@code 0},
333      * then the item at index {@code 1}, and so on.
334      *
335      * @return  an enumeration of the components of this vector
336      * @see     Iterator
337      */
338     public Enumeration<E> elements() {
339         return new Enumeration<E>() {
340             int count = 0;
341 
342             public boolean hasMoreElements() {
343                 return count < elementCount;
344             }
345 
346             public E nextElement() {
347                 synchronized (Vector.this) {
348                     if (count < elementCount) {
349                         return elementData(count++);
350                     }
351                 }
352                 throw new NoSuchElementException("Vector Enumeration");
353             }
354         };
355     }
356 
357     /**
358      * Returns {@code true} if this vector contains the specified element.
359      * More formally, returns {@code true} if and only if this vector
360      * contains at least one element {@code e} such that
361      * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
362      *
363      * @param o element whose presence in this vector is to be tested
364      * @return {@code true} if this vector contains the specified element
365      */
366     public boolean contains(Object o) {
367         return indexOf(o, 0) >= 0;
368     }
369 
370     /**
371      * Returns the index of the first occurrence of the specified element
372      * in this vector, or -1 if this vector does not contain the element.
373      * More formally, returns the lowest index {@code i} such that
374      * <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>,
375      * or -1 if there is no such index.
376      *
377      * @param o element to search for
378      * @return the index of the first occurrence of the specified element in
379      *         this vector, or -1 if this vector does not contain the element
380      */
381     public int indexOf(Object o) {
382         return indexOf(o, 0);
383     }
384 
385     /**
386      * Returns the index of the first occurrence of the specified element in
387      * this vector, searching forwards from {@code index}, or returns -1 if
388      * the element is not found.
389      * More formally, returns the lowest index {@code i} such that
390      * <tt>(i&nbsp;&gt;=&nbsp;index&nbsp;&amp;&amp;&nbsp;(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i))))</tt>,
391      * or -1 if there is no such index.
392      *
393      * @param o element to search for
394      * @param index index to start searching from
395      * @return the index of the first occurrence of the element in
396      *         this vector at position {@code index} or later in the vector;
397      *         {@code -1} if the element is not found.
398      * @throws IndexOutOfBoundsException if the specified index is negative
399      * @see     Object#equals(Object)
400      */
401     public synchronized int indexOf(Object o, int index) {
402         if (o == null) {
403             for (int i = index ; i < elementCount ; i++)
404                 if (elementData[i]==null)
405                     return i;
406         } else {
407             for (int i = index ; i < elementCount ; i++)
408                 if (o.equals(elementData[i]))
409                     return i;
410         }
411         return -1;
412     }
413 
414     /**
415      * Returns the index of the last occurrence of the specified element
416      * in this vector, or -1 if this vector does not contain the element.
417      * More formally, returns the highest index {@code i} such that
418      * <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>,
419      * or -1 if there is no such index.
420      *
421      * @param o element to search for
422      * @return the index of the last occurrence of the specified element in
423      *         this vector, or -1 if this vector does not contain the element
424      */
425     public synchronized int lastIndexOf(Object o) {
426         return lastIndexOf(o, elementCount-1);
427     }
428 
429     /**
430      * Returns the index of the last occurrence of the specified element in
431      * this vector, searching backwards from {@code index}, or returns -1 if
432      * the element is not found.
433      * More formally, returns the highest index {@code i} such that
434      * <tt>(i&nbsp;&lt;=&nbsp;index&nbsp;&amp;&amp;&nbsp;(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i))))</tt>,
435      * or -1 if there is no such index.
436      *
437      * @param o element to search for
438      * @param index index to start searching backwards from
439      * @return the index of the last occurrence of the element at position
440      *         less than or equal to {@code index} in this vector;
441      *         -1 if the element is not found.
442      * @throws IndexOutOfBoundsException if the specified index is greater
443      *         than or equal to the current size of this vector
444      */
445     public synchronized int lastIndexOf(Object o, int index) {
446         if (index >= elementCount)
447             throw new IndexOutOfBoundsException(index + " >= "+ elementCount);
448 
449         if (o == null) {
450             for (int i = index; i >= 0; i--)
451                 if (elementData[i]==null)
452                     return i;
453         } else {
454             for (int i = index; i >= 0; i--)
455                 if (o.equals(elementData[i]))
456                     return i;
457         }
458         return -1;
459     }
460 
461     /**
462      * Returns the component at the specified index.
463      *
464      * <p>This method is identical in functionality to the {@link #get(int)}
465      * method (which is part of the {@link List} interface).
466      *
467      * @param      index   an index into this vector
468      * @return     the component at the specified index
469      * @throws ArrayIndexOutOfBoundsException if the index is out of range
470      *         ({@code index < 0 || index >= size()})
471      */
472     public synchronized E elementAt(int index) {
473         if (index >= elementCount) {
474             throw new ArrayIndexOutOfBoundsException(index + " >= " + elementCount);
475         }
476 
477         return elementData(index);
478     }
479 
480     /**
481      * Returns the first component (the item at index {@code 0}) of
482      * this vector.
483      *
484      * @return     the first component of this vector
485      * @throws NoSuchElementException if this vector has no components
486      */
487     public synchronized E firstElement() {
488         if (elementCount == 0) {
489             throw new NoSuchElementException();
490         }
491         return elementData(0);
492     }
493 
494     /**
495      * Returns the last component of the vector.
496      *
497      * @return  the last component of the vector, i.e., the component at index
498      *          <code>size()&nbsp;-&nbsp;1</code>.
499      * @throws NoSuchElementException if this vector is empty
500      */
501     public synchronized E lastElement() {
502         if (elementCount == 0) {
503             throw new NoSuchElementException();
504         }
505         return elementData(elementCount - 1);
506     }
507 
508     /**
509      * Sets the component at the specified {@code index} of this
510      * vector to be the specified object. The previous component at that
511      * position is discarded.
512      *
513      * <p>The index must be a value greater than or equal to {@code 0}
514      * and less than the current size of the vector.
515      *
516      * <p>This method is identical in functionality to the
517      * {@link #set(int, Object) set(int, E)}
518      * method (which is part of the {@link List} interface). Note that the
519      * {@code set} method reverses the order of the parameters, to more closely
520      * match array usage.  Note also that the {@code set} method returns the
521      * old value that was stored at the specified position.
522      *
523      * @param      obj     what the component is to be set to
524      * @param      index   the specified index
525      * @throws ArrayIndexOutOfBoundsException if the index is out of range
526      *         ({@code index < 0 || index >= size()})
527      */
528     public synchronized void setElementAt(E obj, int index) {
529         if (index >= elementCount) {
530             throw new ArrayIndexOutOfBoundsException(index + " >= " +
531                                                      elementCount);
532         }
533         elementData[index] = obj;
534     }
535 
536     /**
537      * Deletes the component at the specified index. Each component in
538      * this vector with an index greater or equal to the specified
539      * {@code index} is shifted downward to have an index one
540      * smaller than the value it had previously. The size of this vector
541      * is decreased by {@code 1}.
542      *
543      * <p>The index must be a value greater than or equal to {@code 0}
544      * and less than the current size of the vector.
545      *
546      * <p>This method is identical in functionality to the {@link #remove(int)}
547      * method (which is part of the {@link List} interface).  Note that the
548      * {@code remove} method returns the old value that was stored at the
549      * specified position.
550      *
551      * @param      index   the index of the object to remove
552      * @throws ArrayIndexOutOfBoundsException if the index is out of range
553      *         ({@code index < 0 || index >= size()})
554      */
555     public synchronized void removeElementAt(int index) {
556         modCount++;
557         if (index >= elementCount) {
558             throw new ArrayIndexOutOfBoundsException(index + " >= " +
559                                                      elementCount);
560         }
561         else if (index < 0) {
562             throw new ArrayIndexOutOfBoundsException(index);
563         }
564         int j = elementCount - index - 1;
565         if (j > 0) {
566             System.arraycopy(elementData, index + 1, elementData, index, j);
567         }
568         elementCount--;
569         elementData[elementCount] = null; /* to let gc do its work */
570     }
571 
572     /**
573      * Inserts the specified object as a component in this vector at the
574      * specified {@code index}. Each component in this vector with
575      * an index greater or equal to the specified {@code index} is
576      * shifted upward to have an index one greater than the value it had
577      * previously.
578      *
579      * <p>The index must be a value greater than or equal to {@code 0}
580      * and less than or equal to the current size of the vector. (If the
581      * index is equal to the current size of the vector, the new element
582      * is appended to the Vector.)
583      *
584      * <p>This method is identical in functionality to the
585      * {@link #add(int, Object) add(int, E)}
586      * method (which is part of the {@link List} interface).  Note that the
587      * {@code add} method reverses the order of the parameters, to more closely
588      * match array usage.
589      *
590      * @param      obj     the component to insert
591      * @param      index   where to insert the new component
592      * @throws ArrayIndexOutOfBoundsException if the index is out of range
593      *         ({@code index < 0 || index > size()})
594      */
595     public synchronized void insertElementAt(E obj, int index) {
596         modCount++;
597         if (index > elementCount) {
598             throw new ArrayIndexOutOfBoundsException(index
599                                                      + " > " + elementCount);
600         }
601         ensureCapacityHelper(elementCount + 1);
602         System.arraycopy(elementData, index, elementData, index + 1, elementCount - index);
603         elementData[index] = obj;
604         elementCount++;
605     }
606 
607     /**
608      * Adds the specified component to the end of this vector,
609      * increasing its size by one. The capacity of this vector is
610      * increased if its size becomes greater than its capacity.
611      *
612      * <p>This method is identical in functionality to the
613      * {@link #add(Object) add(E)}
614      * method (which is part of the {@link List} interface).
615      *
616      * @param   obj   the component to be added
617      */
618     public synchronized void addElement(E obj) {
619         modCount++;
620         ensureCapacityHelper(elementCount + 1);
621         elementData[elementCount++] = obj;
622     }
623 
624     /**
625      * Removes the first (lowest-indexed) occurrence of the argument
626      * from this vector. If the object is found in this vector, each
627      * component in the vector with an index greater or equal to the
628      * object's index is shifted downward to have an index one smaller
629      * than the value it had previously.
630      *
631      * <p>This method is identical in functionality to the
632      * {@link #remove(Object)} method (which is part of the
633      * {@link List} interface).
634      *
635      * @param   obj   the component to be removed
636      * @return  {@code true} if the argument was a component of this
637      *          vector; {@code false} otherwise.
638      */
639     public synchronized boolean removeElement(Object obj) {
640         modCount++;
641         int i = indexOf(obj);
642         if (i >= 0) {
643             removeElementAt(i);
644             return true;
645         }
646         return false;
647     }
648 
649     /**
650      * Removes all components from this vector and sets its size to zero.
651      *
652      * <p>This method is identical in functionality to the {@link #clear}
653      * method (which is part of the {@link List} interface).
654      */
655     public synchronized void removeAllElements() {
656         modCount++;
657         // Let gc do its work
658         for (int i = 0; i < elementCount; i++)
659             elementData[i] = null;
660 
661         elementCount = 0;
662     }
663 
664     /**
665      * Returns a clone of this vector. The copy will contain a
666      * reference to a clone of the internal data array, not a reference
667      * to the original internal data array of this {@code Vector} object.
668      *
669      * @return  a clone of this vector
670      */
671     public synchronized Object clone() {
672         try {
673             @SuppressWarnings("unchecked")
674                 Vector<E> v = (Vector<E>) super.clone();
675             v.elementData = Arrays.copyOf(elementData, elementCount);
676             v.modCount = 0;
677             return v;
678         } catch (CloneNotSupportedException e) {
679             // this shouldn't happen, since we are Cloneable
680             throw new InternalError(e);
681         }
682     }
683 
684     /**
685      * Returns an array containing all of the elements in this Vector
686      * in the correct order.
687      *
688      * @since 1.2
689      */
690     public synchronized Object[] toArray() {
691         return Arrays.copyOf(elementData, elementCount);
692     }
693 
694     /**
695      * Returns an array containing all of the elements in this Vector in the
696      * correct order; the runtime type of the returned array is that of the
697      * specified array.  If the Vector fits in the specified array, it is
698      * returned therein.  Otherwise, a new array is allocated with the runtime
699      * type of the specified array and the size of this Vector.
700      *
701      * <p>If the Vector fits in the specified array with room to spare
702      * (i.e., the array has more elements than the Vector),
703      * the element in the array immediately following the end of the
704      * Vector is set to null.  (This is useful in determining the length
705      * of the Vector <em>only</em> if the caller knows that the Vector
706      * does not contain any null elements.)
707      *
708      * @param a the array into which the elements of the Vector are to
709      *          be stored, if it is big enough; otherwise, a new array of the
710      *          same runtime type is allocated for this purpose.
711      * @return an array containing the elements of the Vector
712      * @throws ArrayStoreException if the runtime type of a is not a supertype
713      * of the runtime type of every element in this Vector
714      * @throws NullPointerException if the given array is null
715      * @since 1.2
716      */
717     @SuppressWarnings("unchecked")
718     public synchronized <T> T[] toArray(T[] a) {
719         if (a.length < elementCount)
720             return (T[]) Arrays.copyOf(elementData, elementCount, a.getClass());
721 
722         System.arraycopy(elementData, 0, a, 0, elementCount);
723 
724         if (a.length > elementCount)
725             a[elementCount] = null;
726 
727         return a;
728     }
729 
730     // Positional Access Operations
731 
732     @SuppressWarnings("unchecked")
733     E elementData(int index) {
734         return (E) elementData[index];
735     }
736 
737     /**
738      * Returns the element at the specified position in this Vector.
739      *
740      * @param index index of the element to return
741      * @return object at the specified index
742      * @throws ArrayIndexOutOfBoundsException if the index is out of range
743      *            ({@code index < 0 || index >= size()})
744      * @since 1.2
745      */
746     public synchronized E get(int index) {
747         if (index >= elementCount)
748             throw new ArrayIndexOutOfBoundsException(index);
749 
750         return elementData(index);
751     }
752 
753     /**
754      * Replaces the element at the specified position in this Vector with the
755      * specified element.
756      *
757      * @param index index of the element to replace
758      * @param element element to be stored at the specified position
759      * @return the element previously at the specified position
760      * @throws ArrayIndexOutOfBoundsException if the index is out of range
761      *         ({@code index < 0 || index >= size()})
762      * @since 1.2
763      */
764     public synchronized E set(int index, E element) {
765         if (index >= elementCount)
766             throw new ArrayIndexOutOfBoundsException(index);
767 
768         E oldValue = elementData(index);
769         elementData[index] = element;
770         return oldValue;
771     }
772 
773     /**
774      * Appends the specified element to the end of this Vector.
775      *
776      * @param e element to be appended to this Vector
777      * @return {@code true} (as specified by {@link Collection#add})
778      * @since 1.2
779      */
780     public synchronized boolean add(E e) {
781         modCount++;
782         ensureCapacityHelper(elementCount + 1);
783         elementData[elementCount++] = e;
784         return true;
785     }
786 
787     /**
788      * Removes the first occurrence of the specified element in this Vector
789      * If the Vector does not contain the element, it is unchanged.  More
790      * formally, removes the element with the lowest index i such that
791      * {@code (o==null ? get(i)==null : o.equals(get(i)))} (if such
792      * an element exists).
793      *
794      * @param o element to be removed from this Vector, if present
795      * @return true if the Vector contained the specified element
796      * @since 1.2
797      */
798     public boolean remove(Object o) {
799         return removeElement(o);
800     }
801 
802     /**
803      * Inserts the specified element at the specified position in this Vector.
804      * Shifts the element currently at that position (if any) and any
805      * subsequent elements to the right (adds one to their indices).
806      *
807      * @param index index at which the specified element is to be inserted
808      * @param element element to be inserted
809      * @throws ArrayIndexOutOfBoundsException if the index is out of range
810      *         ({@code index < 0 || index > size()})
811      * @since 1.2
812      */
813     public void add(int index, E element) {
814         insertElementAt(element, index);
815     }
816 
817     /**
818      * Removes the element at the specified position in this Vector.
819      * Shifts any subsequent elements to the left (subtracts one from their
820      * indices).  Returns the element that was removed from the Vector.
821      *
822      * @throws ArrayIndexOutOfBoundsException if the index is out of range
823      *         ({@code index < 0 || index >= size()})
824      * @param index the index of the element to be removed
825      * @return element that was removed
826      * @since 1.2
827      */
828     public synchronized E remove(int index) {
829         modCount++;
830         if (index >= elementCount)
831             throw new ArrayIndexOutOfBoundsException(index);
832         E oldValue = elementData(index);
833 
834         int numMoved = elementCount - index - 1;
835         if (numMoved > 0)
836             System.arraycopy(elementData, index+1, elementData, index,
837                              numMoved);
838         elementData[--elementCount] = null; // Let gc do its work
839 
840         return oldValue;
841     }
842 
843     /**
844      * Removes all of the elements from this Vector.  The Vector will
845      * be empty after this call returns (unless it throws an exception).
846      *
847      * @since 1.2
848      */
849     public void clear() {
850         removeAllElements();
851     }
852 
853     // Bulk Operations
854 
855     /**
856      * Returns true if this Vector contains all of the elements in the
857      * specified Collection.
858      *
859      * @param   c a collection whose elements will be tested for containment
860      *          in this Vector
861      * @return true if this Vector contains all of the elements in the
862      *         specified collection
863      * @throws NullPointerException if the specified collection is null
864      */
865     public synchronized boolean containsAll(Collection<?> c) {
866         return super.containsAll(c);
867     }
868 
869     /**
870      * Appends all of the elements in the specified Collection to the end of
871      * this Vector, in the order that they are returned by the specified
872      * Collection's Iterator.  The behavior of this operation is undefined if
873      * the specified Collection is modified while the operation is in progress.
874      * (This implies that the behavior of this call is undefined if the
875      * specified Collection is this Vector, and this Vector is nonempty.)
876      *
877      * @param c elements to be inserted into this Vector
878      * @return {@code true} if this Vector changed as a result of the call
879      * @throws NullPointerException if the specified collection is null
880      * @since 1.2
881      */
882     public synchronized boolean addAll(Collection<? extends E> c) {
883         modCount++;
884         Object[] a = c.toArray();
885         int numNew = a.length;
886         ensureCapacityHelper(elementCount + numNew);
887         System.arraycopy(a, 0, elementData, elementCount, numNew);
888         elementCount += numNew;
889         return numNew != 0;
890     }
891 
892     /**
893      * Removes from this Vector all of its elements that are contained in the
894      * specified Collection.
895      *
896      * @param c a collection of elements to be removed from the Vector
897      * @return true if this Vector changed as a result of the call
898      * @throws ClassCastException if the types of one or more elements
899      *         in this vector are incompatible with the specified
900      *         collection
901      * (<a href="Collection.html#optional-restrictions">optional</a>)
902      * @throws NullPointerException if this vector contains one or more null
903      *         elements and the specified collection does not support null
904      *         elements
905      * (<a href="Collection.html#optional-restrictions">optional</a>),
906      *         or if the specified collection is null
907      * @since 1.2
908      */
909     public synchronized boolean removeAll(Collection<?> c) {
910         return super.removeAll(c);
911     }
912 
913     /**
914      * Retains only the elements in this Vector that are contained in the
915      * specified Collection.  In other words, removes from this Vector all
916      * of its elements that are not contained in the specified Collection.
917      *
918      * @param c a collection of elements to be retained in this Vector
919      *          (all other elements are removed)
920      * @return true if this Vector changed as a result of the call
921      * @throws ClassCastException if the types of one or more elements
922      *         in this vector are incompatible with the specified
923      *         collection
924      * (<a href="Collection.html#optional-restrictions">optional</a>)
925      * @throws NullPointerException if this vector contains one or more null
926      *         elements and the specified collection does not support null
927      *         elements
928      *         (<a href="Collection.html#optional-restrictions">optional</a>),
929      *         or if the specified collection is null
930      * @since 1.2
931      */
932     public synchronized boolean retainAll(Collection<?> c) {
933         return super.retainAll(c);
934     }
935 
936     /**
937      * Inserts all of the elements in the specified Collection into this
938      * Vector at the specified position.  Shifts the element currently at
939      * that position (if any) and any subsequent elements to the right
940      * (increases their indices).  The new elements will appear in the Vector
941      * in the order that they are returned by the specified Collection's
942      * iterator.
943      *
944      * @param index index at which to insert the first element from the
945      *              specified collection
946      * @param c elements to be inserted into this Vector
947      * @return {@code true} if this Vector changed as a result of the call
948      * @throws ArrayIndexOutOfBoundsException if the index is out of range
949      *         ({@code index < 0 || index > size()})
950      * @throws NullPointerException if the specified collection is null
951      * @since 1.2
952      */
953     public synchronized boolean addAll(int index, Collection<? extends E> c) {
954         modCount++;
955         if (index < 0 || index > elementCount)
956             throw new ArrayIndexOutOfBoundsException(index);
957 
958         Object[] a = c.toArray();
959         int numNew = a.length;
960         ensureCapacityHelper(elementCount + numNew);
961 
962         int numMoved = elementCount - index;
963         if (numMoved > 0)
964             System.arraycopy(elementData, index, elementData, index + numNew,
965                              numMoved);
966 
967         System.arraycopy(a, 0, elementData, index, numNew);
968         elementCount += numNew;
969         return numNew != 0;
970     }
971 
972     /**
973      * Compares the specified Object with this Vector for equality.  Returns
974      * true if and only if the specified Object is also a List, both Lists
975      * have the same size, and all corresponding pairs of elements in the two
976      * Lists are <em>equal</em>.  (Two elements {@code e1} and
977      * {@code e2} are <em>equal</em> if {@code (e1==null ? e2==null :
978      * e1.equals(e2))}.)  In other words, two Lists are defined to be
979      * equal if they contain the same elements in the same order.
980      *
981      * @param o the Object to be compared for equality with this Vector
982      * @return true if the specified Object is equal to this Vector
983      */
984     public synchronized boolean equals(Object o) {
985         return super.equals(o);
986     }
987 
988     /**
989      * Returns the hash code value for this Vector.
990      */
991     public synchronized int hashCode() {
992         return super.hashCode();
993     }
994 
995     /**
996      * Returns a string representation of this Vector, containing
997      * the String representation of each element.
998      */
999     public synchronized String toString() {
1000         return super.toString();
1001     }
1002 
1003     /**
1004      * Returns a view of the portion of this List between fromIndex,
1005      * inclusive, and toIndex, exclusive.  (If fromIndex and toIndex are
1006      * equal, the returned List is empty.)  The returned List is backed by this
1007      * List, so changes in the returned List are reflected in this List, and
1008      * vice-versa.  The returned List supports all of the optional List
1009      * operations supported by this List.
1010      *
1011      * <p>This method eliminates the need for explicit range operations (of
1012      * the sort that commonly exist for arrays).  Any operation that expects
1013      * a List can be used as a range operation by operating on a subList view
1014      * instead of a whole List.  For example, the following idiom
1015      * removes a range of elements from a List:
1016      * <pre>
1017      *      list.subList(from, to).clear();
1018      * </pre>
1019      * Similar idioms may be constructed for indexOf and lastIndexOf,
1020      * and all of the algorithms in the Collections class can be applied to
1021      * a subList.
1022      *
1023      * <p>The semantics of the List returned by this method become undefined if
1024      * the backing list (i.e., this List) is <i>structurally modified</i> in
1025      * any way other than via the returned List.  (Structural modifications are
1026      * those that change the size of the List, or otherwise perturb it in such
1027      * a fashion that iterations in progress may yield incorrect results.)
1028      *
1029      * @param fromIndex low endpoint (inclusive) of the subList
1030      * @param toIndex high endpoint (exclusive) of the subList
1031      * @return a view of the specified range within this List
1032      * @throws IndexOutOfBoundsException if an endpoint index value is out of range
1033      *         {@code (fromIndex < 0 || toIndex > size)}
1034      * @throws IllegalArgumentException if the endpoint indices are out of order
1035      *         {@code (fromIndex > toIndex)}
1036      */
1037     public synchronized List<E> subList(int fromIndex, int toIndex) {
1038         return Collections.synchronizedList(super.subList(fromIndex, toIndex),
1039                                             this);
1040     }
1041 
1042     /**
1043      * Removes from this list all of the elements whose index is between
1044      * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
1045      * Shifts any succeeding elements to the left (reduces their index).
1046      * This call shortens the list by {@code (toIndex - fromIndex)} elements.
1047      * (If {@code toIndex==fromIndex}, this operation has no effect.)
1048      */
1049     protected synchronized void removeRange(int fromIndex, int toIndex) {
1050         modCount++;
1051         int numMoved = elementCount - toIndex;
1052         System.arraycopy(elementData, toIndex, elementData, fromIndex,
1053                          numMoved);
1054 
1055         // Let gc do its work
1056         int newElementCount = elementCount - (toIndex-fromIndex);
1057         while (elementCount != newElementCount)
1058             elementData[--elementCount] = null;
1059     }
1060 
1061     /**
1062      * Save the state of the {@code Vector} instance to a stream (that
1063      * is, serialize it).
1064      * This method performs synchronization to ensure the consistency
1065      * of the serialized data.
1066      */
1067     private void writeObject(java.io.ObjectOutputStream s)
1068             throws java.io.IOException {
1069         final java.io.ObjectOutputStream.PutField fields = s.putFields();
1070         final Object[] data;
1071         synchronized (this) {
1072             fields.put("capacityIncrement", capacityIncrement);
1073             fields.put("elementCount", elementCount);
1074             data = elementData.clone();
1075         }
1076         fields.put("elementData", data);
1077         s.writeFields();
1078     }
1079 
1080     /**
1081      * Returns a list iterator over the elements in this list (in proper
1082      * sequence), starting at the specified position in the list.
1083      * The specified index indicates the first element that would be
1084      * returned by an initial call to {@link ListIterator#next next}.
1085      * An initial call to {@link ListIterator#previous previous} would
1086      * return the element with the specified index minus one.
1087      *
1088      * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
1089      *
1090      * @throws IndexOutOfBoundsException {@inheritDoc}
1091      */
1092     public synchronized ListIterator<E> listIterator(int index) {
1093         if (index < 0 || index > elementCount)
1094             throw new IndexOutOfBoundsException("Index: "+index);
1095         return new ListItr(index);
1096     }
1097 
1098     /**
1099      * Returns a list iterator over the elements in this list (in proper
1100      * sequence).
1101      *
1102      * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
1103      *
1104      * @see #listIterator(int)
1105      */
1106     public synchronized ListIterator<E> listIterator() {
1107         return new ListItr(0);
1108     }
1109 
1110     /**
1111      * Returns an iterator over the elements in this list in proper sequence.
1112      *
1113      * <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
1114      *
1115      * @return an iterator over the elements in this list in proper sequence
1116      */
1117     public synchronized Iterator<E> iterator() {
1118         return new Itr();
1119     }
1120 
1121     /**
1122      * An optimized version of AbstractList.Itr
1123      */
1124     private class Itr implements Iterator<E> {
1125         int cursor;       // index of next element to return
1126         int lastRet = -1; // index of last element returned; -1 if no such
1127         int expectedModCount = modCount;
1128 
1129         public boolean hasNext() {
1130             // Racy but within spec, since modifications are checked
1131             // within or after synchronization in next/previous
1132             return cursor != elementCount;
1133         }
1134 
1135         public E next() {
1136             synchronized (Vector.this) {
1137                 checkForComodification();
1138                 int i = cursor;
1139                 if (i >= elementCount)
1140                     throw new NoSuchElementException();
1141                 cursor = i + 1;
1142                 return elementData(lastRet = i);
1143             }
1144         }
1145 
1146         public void remove() {
1147             if (lastRet == -1)
1148                 throw new IllegalStateException();
1149             synchronized (Vector.this) {
1150                 checkForComodification();
1151                 Vector.this.remove(lastRet);
1152                 expectedModCount = modCount;
1153             }
1154             cursor = lastRet;
1155             lastRet = -1;
1156         }
1157 
1158         @Override
1159         public void forEachRemaining(Consumer<? super E> action) {
1160             Objects.requireNonNull(action);
1161             synchronized (Vector.this) {
1162                 final int size = elementCount;
1163                 int i = cursor;
1164                 if (i >= size) {
1165                     return;
1166                 }
1167         @SuppressWarnings("unchecked")
1168                 final E[] elementData = (E[]) Vector.this.elementData;
1169                 if (i >= elementData.length) {
1170                     throw new ConcurrentModificationException();
1171                 }
1172                 while (i != size && modCount == expectedModCount) {
1173                     action.accept(elementData[i++]);
1174                 }
1175                 // update once at end of iteration to reduce heap write traffic
1176                 cursor = i;
1177                 lastRet = i - 1;
1178                 checkForComodification();
1179             }
1180         }
1181 
1182         final void checkForComodification() {
1183             if (modCount != expectedModCount)
1184                 throw new ConcurrentModificationException();
1185         }
1186     }
1187 
1188     /**
1189      * An optimized version of AbstractList.ListItr
1190      */
1191     final class ListItr extends Itr implements ListIterator<E> {
1192         ListItr(int index) {
1193             super();
1194             cursor = index;
1195         }
1196 
1197         public boolean hasPrevious() {
1198             return cursor != 0;
1199         }
1200 
1201         public int nextIndex() {
1202             return cursor;
1203         }
1204 
1205         public int previousIndex() {
1206             return cursor - 1;
1207         }
1208 
1209         public E previous() {
1210             synchronized (Vector.this) {
1211                 checkForComodification();
1212                 int i = cursor - 1;
1213                 if (i < 0)
1214                     throw new NoSuchElementException();
1215                 cursor = i;
1216                 return elementData(lastRet = i);
1217             }
1218         }
1219 
1220         public void set(E e) {
1221             if (lastRet == -1)
1222                 throw new IllegalStateException();
1223             synchronized (Vector.this) {
1224                 checkForComodification();
1225                 Vector.this.set(lastRet, e);
1226             }
1227         }
1228 
1229         public void add(E e) {
1230             int i = cursor;
1231             synchronized (Vector.this) {
1232                 checkForComodification();
1233                 Vector.this.add(i, e);
1234                 expectedModCount = modCount;
1235             }
1236             cursor = i + 1;
1237             lastRet = -1;
1238         }
1239     }
1240 
1241     @Override
1242     public synchronized void forEach(Consumer<? super E> action) {
1243         Objects.requireNonNull(action);
1244         final int expectedModCount = modCount;
1245         @SuppressWarnings("unchecked")
1246         final E[] elementData = (E[]) this.elementData;
1247         final int elementCount = this.elementCount;
1248         for (int i=0; modCount == expectedModCount && i < elementCount; i++) {
1249             action.accept(elementData[i]);
1250         }
1251         if (modCount != expectedModCount) {
1252             throw new ConcurrentModificationException();
1253         }
1254     }
1255 
1256     @Override
1257     @SuppressWarnings("unchecked")
1258     public synchronized boolean removeIf(Predicate<? super E> filter) {
1259         Objects.requireNonNull(filter);
1260         // figure out which elements are to be removed
1261         // any exception thrown from the filter predicate at this stage
1262         // will leave the collection unmodified
1263         int removeCount = 0;
1264         final int size = elementCount;
1265         final BitSet removeSet = new BitSet(size);
1266         final int expectedModCount = modCount;
1267         for (int i=0; modCount == expectedModCount && i < size; i++) {
1268             @SuppressWarnings("unchecked")
1269             final E element = (E) elementData[i];
1270             if (filter.test(element)) {
1271                 removeSet.set(i);
1272                 removeCount++;
1273             }
1274         }
1275         if (modCount != expectedModCount) {
1276             throw new ConcurrentModificationException();
1277         }
1278 
1279         // shift surviving elements left over the spaces left by removed elements
1280         final boolean anyToRemove = removeCount > 0;
1281         if (anyToRemove) {
1282             final int newSize = size - removeCount;
1283             for (int i=0, j=0; (i < size) && (j < newSize); i++, j++) {
1284                 i = removeSet.nextClearBit(i);
1285                 elementData[j] = elementData[i];
1286             }
1287             for (int k=newSize; k < size; k++) {
1288                 elementData[k] = null;  // Let gc do its work
1289             }
1290             elementCount = newSize;
1291             if (modCount != expectedModCount) {
1292                 throw new ConcurrentModificationException();
1293             }
1294             modCount++;
1295         }
1296 
1297         return anyToRemove;
1298     }
1299 
1300     @Override
1301     @SuppressWarnings("unchecked")
1302     public synchronized void replaceAll(UnaryOperator<E> operator) {
1303         Objects.requireNonNull(operator);
1304         final int expectedModCount = modCount;
1305         final int size = elementCount;
1306         for (int i=0; modCount == expectedModCount && i < size; i++) {
1307             elementData[i] = operator.apply((E) elementData[i]);
1308         }
1309         if (modCount != expectedModCount) {
1310             throw new ConcurrentModificationException();
1311         }
1312         modCount++;
1313     }
1314 
1315     @SuppressWarnings("unchecked")
1316     @Override
1317     public synchronized void sort(Comparator<? super E> c) {
1318         final int expectedModCount = modCount;
1319         Arrays.sort((E[]) elementData, 0, elementCount, c);
1320         if (modCount != expectedModCount) {
1321             throw new ConcurrentModificationException();
1322         }
1323         modCount++;
1324     }
1325 
1326     /**
1327      * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
1328      * and <em>fail-fast</em> {@link Spliterator} over the elements in this
1329      * list.
1330      *
1331      * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
1332      * {@link Spliterator#SUBSIZED}, and {@link Spliterator#ORDERED}.
1333      * Overriding implementations should document the reporting of additional
1334      * characteristic values.
1335      *
1336      * @return a {@code Spliterator} over the elements in this list
1337      * @since 1.8
1338      */
1339     @Override
1340     public Spliterator<E> spliterator() {
1341         return new VectorSpliterator<>(this, null, 0, -1, 0);
1342     }
1343 
1344     /** Similar to ArrayList Spliterator */
1345     static final class VectorSpliterator<E> implements Spliterator<E> {
1346         private final Vector<E> list;
1347         private Object[] array;
1348         private int index; // current index, modified on advance/split
1349         private int fence; // -1 until used; then one past last index
1350         private int expectedModCount; // initialized when fence set
1351 
1352         /** Create new spliterator covering the given  range */
1353         VectorSpliterator(Vector<E> list, Object[] array, int origin, int fence,
1354                           int expectedModCount) {
1355             this.list = list;
1356             this.array = array;
1357             this.index = origin;
1358             this.fence = fence;
1359             this.expectedModCount = expectedModCount;
1360         }
1361 
1362         private int getFence() { // initialize on first use
1363             int hi;
1364             if ((hi = fence) < 0) {
1365                 synchronized(list) {
1366                     array = list.elementData;
1367                     expectedModCount = list.modCount;
1368                     hi = fence = list.elementCount;
1369                 }
1370             }
1371             return hi;
1372         }
1373 
1374         public Spliterator<E> trySplit() {
1375             int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
1376             return (lo >= mid) ? null :
1377                 new VectorSpliterator<E>(list, array, lo, index = mid,
1378                                          expectedModCount);
1379         }
1380 
1381         @SuppressWarnings("unchecked")
1382         public boolean tryAdvance(Consumer<? super E> action) {
1383             int i;
1384             if (action == null)
1385                 throw new NullPointerException();
1386             if (getFence() > (i = index)) {
1387                 index = i + 1;
1388                 action.accept((E)array[i]);
1389                 if (list.modCount != expectedModCount)
1390                     throw new ConcurrentModificationException();
1391                 return true;
1392             }
1393             return false;
1394         }
1395 
1396         @SuppressWarnings("unchecked")
1397         public void forEachRemaining(Consumer<? super E> action) {
1398             int i, hi; // hoist accesses and checks from loop
1399             Vector<E> lst; Object[] a;
1400             if (action == null)
1401                 throw new NullPointerException();
1402             if ((lst = list) != null) {
1403                 if ((hi = fence) < 0) {
1404                     synchronized(lst) {
1405                         expectedModCount = lst.modCount;
1406                         a = array = lst.elementData;
1407                         hi = fence = lst.elementCount;
1408                     }
1409                 }
1410                 else
1411                     a = array;
1412                 if (a != null && (i = index) >= 0 && (index = hi) <= a.length) {
1413                     while (i < hi)
1414                         action.accept((E) a[i++]);
1415                     if (lst.modCount == expectedModCount)
1416                         return;
1417                 }
1418             }
1419             throw new ConcurrentModificationException();
1420         }
1421 
1422         public long estimateSize() {
1423             return (long) (getFence() - index);
1424         }
1425 
1426         public int characteristics() {
1427             return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
1428         }
1429     }
1430 }