vector与ArrayList、hashmap与hashtable区别

一、vector与ArrayList区别

    首先要说明的是vector和arraylist都是list的实现类，都是代表链表的数据结构。

    java.util.Vector;  类中

1.   1 package java.util;
     2 publicclassVector<E>
     3 extendsAbstractList<E>
     4 implementsList<E>,RandomAccess,Cloneable, java.io.Serializable
     5 {
     6 protectedObject[] elementData;
     7 protectedint elementCount;
     8 protectedint capacityIncrement;
     9 privatestaticfinallong serialVersionUID =-2767605614048989439L;
    10 publicVector(int initialCapacity,int capacityIncrement){
    11 super();
    12 if(initialCapacity <0)
    13 thrownewIllegalArgumentException("Illegal Capacity: "+
    14 initialCapacity);
    15 this.elementData =newObject[initialCapacity];
    16 this.capacityIncrement = capacityIncrement;
    17 }
    18 publicVector(int initialCapacity){
    19 this(initialCapacity,0);
    20 }
    21 publicVector(){
    22 this(10);
    23 }
    24 publicVector(Collection<?extends E> c){
    25 elementData = c.toArray();
    26 elementCount = elementData.length;
    27 // c.toArray might (incorrectly) not return Object[] (see 6260652)
    28 if(elementData.getClass()!=Object[].class)
    29 elementData =Arrays.copyOf(elementData, elementCount,Object[].class);
    30 }
    31 publicsynchronizedvoid copyInto(Object[] anArray){
    32 System.arraycopy(elementData,0, anArray,0, elementCount);
    33 }
    34 /**
    35 * Trims the capacity of this vector to be the vector's current
    36 * size. If the capacity of this vector is larger than its current
    37 * size, then the capacity is changed to equal the size by replacing
    38 * its internal data array, kept in the field {@code elementData},
    39 * with a smaller one. An application can use this operation to
    40 * minimize the storage of a vector.
    41 */
    42 publicsynchronizedvoid trimToSize(){
    43 modCount++;
    44 int oldCapacity = elementData.length;
    45 if(elementCount < oldCapacity){
    46 elementData =Arrays.copyOf(elementData, elementCount);
    47 }
    48 }
    49 publicsynchronizedvoid ensureCapacity(int minCapacity){
    50 modCount++;
    51 ensureCapacityHelper(minCapacity);
    52 }
    53 /**
    54 * This implements the unsynchronized semantics of ensureCapacity.
    55 * Synchronized methods in this class can internally call this
    56 * method for ensuring capacity without incurring the cost of an
    57 * extra synchronization.
    58 *
    59 * @see #ensureCapacity(int)
    60 */
    61 privatevoid ensureCapacityHelper(int minCapacity){
    62 int oldCapacity = elementData.length;
    63 if(minCapacity > oldCapacity){
    64 Object[] oldData = elementData;
    65 int newCapacity =(capacityIncrement >0)?
    66 (oldCapacity + capacityIncrement):(oldCapacity *2);
    67 if(newCapacity < minCapacity){
    68 newCapacity = minCapacity;
    69 }
    70 elementData =Arrays.copyOf(elementData, newCapacity);
    71 }
    72 }
    73 /**
    74 * Sets the size of this vector. If the new size is greater than the
    75 * current size, new {@code null} items are added to the end of
    76 * the vector. If the new size is less than the current size, all
    77 * components at index {@code newSize} and greater are discarded.
    78 *
    79 * @param newSize the new size of this vector
    80 * @throws ArrayIndexOutOfBoundsException if the new size is negative
    81 */
    82 publicsynchronizedvoid setSize(int newSize){
    83 modCount++;
    84 if(newSize > elementCount){
    85 ensureCapacityHelper(newSize);
    86 }else{
    87 for(int i = newSize ; i < elementCount ; i++){
    88 elementData[i]=null;
    89 }
    90 }
    91 elementCount = newSize;
    92 }
    93 /**
    94 * Returns the current capacity of this vector.
    95 *
    96 * @return the current capacity (the length of its internal
    97 * data array, kept in the field {@code elementData}
    98 * of this vector)
    99 */
   100 publicsynchronizedint capacity(){
   101 return elementData.length;
   102 }
   103 /**
   104 * Returns the number of components in this vector.
   105 *
   106 * @return the number of components in this vector
   107 */
   108 publicsynchronizedint size(){
   109 return elementCount;
   110 }
   111 /**
   112 * Tests if this vector has no components.
   113 *
   114 * @return {@code true} if and only if this vector has
   115 * no components, that is, its size is zero;
   116 * {@code false} otherwise.
   117 */
   118 publicsynchronizedboolean isEmpty(){
   119 return elementCount ==0;
   120 }
   121 /**
   122 * Returns an enumeration of the components of this vector. The
   123 * returned {@code Enumeration} object will generate all items in
   124 * this vector. The first item generated is the item at index {@code 0},
   125 * then the item at index {@code 1}, and so on.
   126 *
   127 * @return an enumeration of the components of this vector
   128 * @see Iterator
   129 */
   130 publicEnumeration<E> elements(){
   131 returnnewEnumeration<E>(){
   132 int count =0;
   133 publicboolean hasMoreElements(){
   134 return count < elementCount;
   135 }
   136 public E nextElement(){
   137 synchronized(Vector.this){
   138 if(count < elementCount){
   139 return(E)elementData[count++];
   140 }
   141 }
   142 thrownewNoSuchElementException("Vector Enumeration");
   143 }
   144 };
   145 }
   146 /**
   147 * Returns {@code true} if this vector contains the specified element.
   148 * More formally, returns {@code true} if and only if this vector
   149 * contains at least one element {@code e} such that
   150 * <tt>(o==null ? e==null : o.equals(e))</tt>.
   151 *
   152 * @param o element whose presence in this vector is to be tested
   153 * @return {@code true} if this vector contains the specified element
   154 */
   155 publicboolean contains(Object o){
   156 return indexOf(o,0)>=0;
   157 }
   158 /**
   159 * Returns the index of the first occurrence of the specified element
   160 * in this vector, or -1 if this vector does not contain the element.
   161 * More formally, returns the lowest index {@code i} such that
   162 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
   163 * or -1 if there is no such index.
   164 *
   165 * @param o element to search for
   166 * @return the index of the first occurrence of the specified element in
   167 * this vector, or -1 if this vector does not contain the element
   168 */
   169 publicint indexOf(Object o){
   170 return indexOf(o,0);
   171 }
   172 /**
   173 * Returns the index of the first occurrence of the specified element in
   174 * this vector, searching forwards from {@code index}, or returns -1 if
   175 * the element is not found.
   176 * More formally, returns the lowest index {@code i} such that
   177 * <tt>(i >= index && (o==null ? get(i)==null : o.equals(get(i))))</tt>,
   178 * or -1 if there is no such index.
   179 *
   180 * @param o element to search for
   181 * @param index index to start searching from
   182 * @return the index of the first occurrence of the element in
   183 * this vector at position {@code index} or later in the vector;
   184 * {@code -1} if the element is not found.
   185 * @throws IndexOutOfBoundsException if the specified index is negative
   186 * @see Object#equals(Object)
   187 */
   188 publicsynchronizedint indexOf(Object o,int index){
   189 if(o ==null){
   190 for(int i = index ; i < elementCount ; i++)
   191 if(elementData[i]==null)
   192 return i;
   193 }else{
   194 for(int i = index ; i < elementCount ; i++)
   195 if(o.equals(elementData[i]))
   196 return i;
   197 }
   198 return-1;
   199 }
   200 /**
   201 * Returns the index of the last occurrence of the specified element
   202 * in this vector, or -1 if this vector does not contain the element.
   203 * More formally, returns the highest index {@code i} such that
   204 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
   205 * or -1 if there is no such index.
   206 *
   207 * @param o element to search for
   208 * @return the index of the last occurrence of the specified element in
   209 * this vector, or -1 if this vector does not contain the element
   210 */
   211 publicsynchronizedint lastIndexOf(Object o){
   212 return lastIndexOf(o, elementCount-1);
   213 }
   214 /**
   215 * Returns the index of the last occurrence of the specified element in
   216 * this vector, searching backwards from {@code index}, or returns -1 if
   217 * the element is not found.
   218 * More formally, returns the highest index {@code i} such that
   219 * <tt>(i <= index && (o==null ? get(i)==null : o.equals(get(i))))</tt>,
   220 * or -1 if there is no such index.
   221 *
   222 * @param o element to search for
   223 * @param index index to start searching backwards from
   224 * @return the index of the last occurrence of the element at position
   225 * less than or equal to {@code index} in this vector;
   226 * -1 if the element is not found.
   227 * @throws IndexOutOfBoundsException if the specified index is greater
   228 * than or equal to the current size of this vector
   229 */
   230 publicsynchronizedint lastIndexOf(Object o,int index){
   231 if(index >= elementCount)
   232 thrownewIndexOutOfBoundsException(index +" >= "+ elementCount);
   233 if(o ==null){
   234 for(int i = index; i >=0; i--)
   235 if(elementData[i]==null)
   236 return i;
   237 }else{
   238 for(int i = index; i >=0; i--)
   239 if(o.equals(elementData[i]))
   240 return i;
   241 }
   242 return-1;
   243 }
   244 /**
   245 * Returns the component at the specified index.
   246 *
   247 * <p>This method is identical in functionality to the {@link #get(int)}
   248 * method (which is part of the {@link List} interface).
   249 *
   250 * @param index an index into this vector
   251 * @return the component at the specified index
   252 * @throws ArrayIndexOutOfBoundsException if the index is out of range
   253 * ({@code index < 0 || index >= size()})
   254 */
   255 publicsynchronized E elementAt(int index){
   256 if(index >= elementCount){
   257 thrownewArrayIndexOutOfBoundsException(index +" >= "+ elementCount);
   258 }
   259 return(E)elementData[index];
   260 }
   261 /**
   262 * Returns the first component (the item at index {@code 0}) of
   263 * this vector.
   264 *
   265 * @return the first component of this vector
   266 * @throws NoSuchElementException if this vector has no components
   267 */
   268 publicsynchronized E firstElement(){
   269 if(elementCount ==0){
   270 thrownewNoSuchElementException();
   271 }
   272 return(E)elementData[0];
   273 }
   274 /**
   275 * Returns the last component of the vector.
   276 *
   277 * @return the last component of the vector, i.e., the component at index
   278 * <code>size() - 1</code>.
   279 * @throws NoSuchElementException if this vector is empty
   280 */
   281 publicsynchronized E lastElement(){
   282 if(elementCount ==0){
   283 thrownewNoSuchElementException();
   284 }
   285 return(E)elementData[elementCount -1];
   286 }
   287 /**
   288 * Sets the component at the specified {@code index} of this
   289 * vector to be the specified object. The previous component at that
   290 * position is discarded.
   291 *
   292 * <p>The index must be a value greater than or equal to {@code 0}
   293 * and less than the current size of the vector.
   294 *
   295 * <p>This method is identical in functionality to the
   296 * {@link #set(int, Object) set(int, E)}
   297 * method (which is part of the {@link List} interface). Note that the
   298 * {@code set} method reverses the order of the parameters, to more closely
   299 * match array usage. Note also that the {@code set} method returns the
   300 * old value that was stored at the specified position.
   301 *
   302 * @param obj what the component is to be set to
   303 * @param index the specified index
   304 * @throws ArrayIndexOutOfBoundsException if the index is out of range
   305 * ({@code index < 0 || index >= size()})
   306 */
   307 publicsynchronizedvoid setElementAt(E obj,int index){
   308 if(index >= elementCount){
   309 thrownewArrayIndexOutOfBoundsException(index +" >= "+
   310 elementCount);
   311 }
   312 elementData[index]= obj;
   313 }
   314 publicsynchronizedvoid removeElementAt(int index){
   315 modCount++;
   316 if(index >= elementCount){
   317 thrownewArrayIndexOutOfBoundsException(index +" >= "+
   318 elementCount);
   319 }
   320 elseif(index <0){
   321 thrownewArrayIndexOutOfBoundsException(index);
   322 }
   323 int j = elementCount - index -1;
   324 if(j >0){
   325 System.arraycopy(elementData, index +1, elementData, index, j);
   326 }
   327 elementCount--;
   328 elementData[elementCount]=null;/* to let gc do its work */
   329 }
   330 /**
   331 * Inserts the specified object as a component in this vector at the
   332 * specified {@code index}. Each component in this vector with
   333 * an index greater or equal to the specified {@code index} is
   334 * shifted upward to have an index one greater than the value it had
   335 * previously.
   336 *
   337 * <p>The index must be a value greater than or equal to {@code 0}
   338 * and less than or equal to the current size of the vector. (If the
   339 * index is equal to the current size of the vector, the new element
   340 * is appended to the Vector.)
   341 *
   342 * <p>This method is identical in functionality to the
   343 * {@link #add(int, Object) add(int, E)}
   344 * method (which is part of the {@link List} interface). Note that the
   345 * {@code add} method reverses the order of the parameters, to more closely
   346 * match array usage.
   347 *
   348 * @param obj the component to insert
   349 * @param index where to insert the new component
   350 * @throws ArrayIndexOutOfBoundsException if the index is out of range
   351 * ({@code index < 0 || index > size()})
   352 */
   353 publicsynchronizedvoid insertElementAt(E obj,int index){
   354 modCount++;
   355 if(index > elementCount){
   356 thrownewArrayIndexOutOfBoundsException(index
   357 +" > "+ elementCount);
   358 }
   359 ensureCapacityHelper(elementCount +1);
   360 System.arraycopy(elementData, index, elementData, index +1, elementCount - index);
   361 elementData[index]= obj;
   362 elementCount++;
   363 }
   364 /**
   365 * Adds the specified component to the end of this vector,
   366 * increasing its size by one. The capacity of this vector is
   367 * increased if its size becomes greater than its capacity.
   368 *
   369 * <p>This method is identical in functionality to the
   370 * {@link #add(Object) add(E)}
   371 * method (which is part of the {@link List} interface).
   372 *
   373 * @param obj the component to be added
   374 */
   375 publicsynchronizedvoid addElement(E obj){
   376 modCount++;
   377 ensureCapacityHelper(elementCount +1);
   378 elementData[elementCount++]= obj;
   379 }
   380 /**
   381 * Removes the first (lowest-indexed) occurrence of the argument
   382 * from this vector. If the object is found in this vector, each
   383 * component in the vector with an index greater or equal to the
   384 * object's index is shifted downward to have an index one smaller
   385 * than the value it had previously.
   386 *
   387 * <p>This method is identical in functionality to the
   388 * {@link #remove(Object)} method (which is part of the
   389 * {@link List} interface).
   390 *
   391 * @param obj the component to be removed
   392 * @return {@code true} if the argument was a component of this
   393 * vector; {@code false} otherwise.
   394 */
   395 publicsynchronizedboolean removeElement(Object obj){
   396 modCount++;
   397 int i = indexOf(obj);
   398 if(i >=0){
   399 removeElementAt(i);
   400 returntrue;
   401 }
   402 returnfalse;
   403 }
   404 /**
   405 * Removes all components from this vector and sets its size to zero.
   406 *
   407 * <p>This method is identical in functionality to the {@link #clear}
   408 * method (which is part of the {@link List} interface).
   409 */
   410 publicsynchronizedvoid removeAllElements(){
   411 modCount++;
   412 // Let gc do its work
   413 for(int i =0; i < elementCount; i++)
   414 elementData[i]=null;
   415 elementCount =0;
   416 }
   417 /**
   418 * Returns a clone of this vector. The copy will contain a
   419 * reference to a clone of the internal data array, not a reference
   420 * to the original internal data array of this {@code Vector} object.
   421 *
   422 * @return a clone of this vector
   423 */
   424 publicsynchronizedObject clone(){
   425 try{
   426 Vector<E> v =(Vector<E>)super.clone();
   427 v.elementData =Arrays.copyOf(elementData, elementCount);
   428 v.modCount =0;
   429 return v;
   430 }catch(CloneNotSupportedException e){
   431 // this shouldn't happen, since we are Cloneable
   432 thrownewInternalError();
   433 }
   434 }
   435 /**
   436 * Returns an array containing all of the elements in this Vector
   437 * in the correct order.
   438 *
   439 * @since 1.2
   440 */
   441 publicsynchronizedObject[] toArray(){
   442 returnArrays.copyOf(elementData, elementCount);
   443 }
   444 publicsynchronized<T> T[] toArray(T[] a){
   445 if(a.length < elementCount)
   446 return(T[])Arrays.copyOf(elementData, elementCount, a.getClass());
   447 System.arraycopy(elementData,0, a,0, elementCount);
   448 if(a.length > elementCount)
   449 a[elementCount]=null;
   450 return a;
   451 }
   452 // Positional Access Operations
   453 /**
   454 * Returns the element at the specified position in this Vector.
   455 *
   456 * @param index index of the element to return
   457 * @return object at the specified index
   458 * @throws ArrayIndexOutOfBoundsException if the index is out of range
   459 * ({@code index < 0 || index >= size()})
   460 * @since 1.2
   461 */
   462 publicsynchronized E get(int index){
   463 if(index >= elementCount)
   464 thrownewArrayIndexOutOfBoundsException(index);
   465 return(E)elementData[index];
   466 }
   467 /**
   468 * Replaces the element at the specified position in this Vector with the
   469 * specified element.
   470 *
   471 * @param index index of the element to replace
   472 * @param element element to be stored at the specified position
   473 * @return the element previously at the specified position
   474 * @throws ArrayIndexOutOfBoundsException if the index is out of range
   475 * ({@code index < 0 || index >= size()})
   476 * @since 1.2
   477 */
   478 publicsynchronized E set(int index, E element){
   479 if(index >= elementCount)
   480 thrownewArrayIndexOutOfBoundsException(index);
   481 Object oldValue = elementData[index];
   482 elementData[index]= element;
   483 return(E)oldValue;
   484 }
   485 /**
   486 * Appends the specified element to the end of this Vector.
   487 *
   488 * @param e element to be appended to this Vector
   489 * @return {@code true} (as specified by {@link Collection#add})
   490 * @since 1.2
   491 */
   492 publicsynchronizedboolean add(E e){
   493 modCount++;
   494 ensureCapacityHelper(elementCount +1);
   495 elementData[elementCount++]= e;
   496 returntrue;
   497 }
   498 publicboolean remove(Object o){
   499 return removeElement(o);
   500 }
   501 publicvoid add(int index, E element){
   502 insertElementAt(element, index);
   503 }
   504 publicsynchronized E remove(int index){
   505 modCount++;
   506 if(index >= elementCount)
   507 thrownewArrayIndexOutOfBoundsException(index);
   508 Object oldValue = elementData[index];
   509 int numMoved = elementCount - index -1;
   510 if(numMoved >0)
   511 System.arraycopy(elementData, index+1, elementData, index,
   512 numMoved);
   513 elementData[--elementCount]=null;// Let gc do its work
   514 return(E)oldValue;
   515 }
   516 publicvoid clear(){
   517 removeAllElements();
   518 }
   519 // Bulk Operations
   520 publicsynchronizedboolean containsAll(Collection<?> c){
   521 returnsuper.containsAll(c);
   522 }
   523 publicsynchronizedboolean addAll(Collection<?extends E> c){
   524 modCount++;
   525 Object[] a = c.toArray();
   526 int numNew = a.length;
   527 ensureCapacityHelper(elementCount + numNew);
   528 System.arraycopy(a,0, elementData, elementCount, numNew);
   529 elementCount += numNew;
   530 return numNew !=0;
   531 }
   532 publicsynchronizedboolean removeAll(Collection<?> c){
   533 returnsuper.removeAll(c);
   534 }
   535 publicsynchronizedboolean retainAll(Collection<?> c){
   536 returnsuper.retainAll(c);
   537 }
   538 publicsynchronizedboolean addAll(int index,Collection<?extends E> c){
   539 modCount++;
   540 if(index <0|| index > elementCount)
   541 thrownewArrayIndexOutOfBoundsException(index);
   542 Object[] a = c.toArray();
   543 int numNew = a.length;
   544 ensureCapacityHelper(elementCount + numNew);
   545 int numMoved = elementCount - index;
   546 if(numMoved >0)
   547 System.arraycopy(elementData, index, elementData, index + numNew,
   548 numMoved);
   549 System.arraycopy(a,0, elementData, index, numNew);
   550 elementCount += numNew;
   551 return numNew !=0;
   552 }
   553 /**
   554 * Compares the specified Object with this Vector for equality. Returns
   555 * true if and only if the specified Object is also a List, both Lists
   556 * have the same size, and all corresponding pairs of elements in the two
   557 * Lists are <em>equal</em>. (Two elements {@code e1} and
   558 * {@code e2} are <em>equal</em> if {@code (e1==null ? e2==null :
   559 * e1.equals(e2))}.) In other words, two Lists are defined to be
   560 * equal if they contain the same elements in the same order.
   561 *
   562 * @param o the Object to be compared for equality with this Vector
   563 * @return true if the specified Object is equal to this Vector
   564 */
   565 publicsynchronizedboolean equals(Object o){
   566 returnsuper.equals(o);
   567 }
   568 /**
   569 * Returns the hash code value for this Vector.
   570 */
   571 publicsynchronizedint hashCode(){
   572 returnsuper.hashCode();
   573 }
   574 /**
   575 * Returns a string representation of this Vector, containing
   576 * the String representation of each element.
   577 */
   578 publicsynchronizedString toString(){
   579 returnsuper.toString();
   580 }
   581 publicsynchronizedList<E> subList(int fromIndex,int toIndex){
   582 returnCollections.synchronizedList(super.subList(fromIndex, toIndex),
   583 this);
   584 }
   585 protectedsynchronizedvoid removeRange(int fromIndex,int toIndex){
   586 modCount++;
   587 int numMoved = elementCount - toIndex;
   588 System.arraycopy(elementData, toIndex, elementData, fromIndex,
   589 numMoved);
   590 // Let gc do its work
   591 int newElementCount = elementCount -(toIndex-fromIndex);
   592 while(elementCount != newElementCount)
   593 elementData[--elementCount]=null;
   594 }
   595 privatesynchronizedvoid writeObject(java.io.ObjectOutputStream s)
   596 throws java.io.IOException
   597 {
   598 s.defaultWriteObject();
   599 }
   600 }

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    说明：vector中使用到了synchronized关键字，也就是说vector是线程安全的！同理可知ArrayList是线程不安全的；