vector与ArrayList、hashmap与hashtable区别

一、vector与ArrayList区别

1.   1 package java.util;
     2 publicclassVector
     3 extendsAbstractList
     4 implementsList,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 elements(){
   131 returnnewEnumeration(){
   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 * (o==null ? e==null : o.equals(e)).
   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 * (o==null ? get(i)==null : o.equals(get(i))),
   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 * (i >= index && (o==null ? get(i)==null : o.equals(get(i)))),
   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 * (o==null ? get(i)==null : o.equals(get(i))),
   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 * (i <= index && (o==null ? get(i)==null : o.equals(get(i)))),
   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 * 
   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 * size() - 1.
   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 * 
   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 * 
   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 * 
   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 * 
   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 * 
   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 * 
   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 * 
   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 v =(Vector)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[] 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 equal. (Two elements {@code e1} and
   558 * {@code e2} are equal 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 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 }

  1     package java.util;
  2     import java.io.*;
  3     publicclassHashMap
  4     extendsAbstractMap
  5     implementsMap,Cloneable,Serializable
  6     {
  7     /**
  8     * The default initial capacity - MUST be a power of two.
  9     */
 10     staticfinalint DEFAULT_INITIAL_CAPACITY =16;
 11     /**
 12     * The maximum capacity, used if a higher value is implicitly specified
 13     * by either of the constructors with arguments.
 14     * MUST be a power of two <= 1<<30.
 15     */
 16     staticfinalint MAXIMUM_CAPACITY =1<<30;
 17     /**
 18     * The load factor used when none specified in constructor.
 19     */
 20     staticfinalfloat DEFAULT_LOAD_FACTOR =0.75f;
 21     /**
 22     * The table, resized as necessary. Length MUST Always be a power of two.
 23     */
 24     transientEntry[] table;
 25     /**
 26     * The number of key-value mappings contained in this map.
 27     */
 28     transientint size;
 29     /**
 30     * The next size value at which to resize (capacity * load factor).
 31     * @serial
 32     */
 33     int threshold;
 34     /**
 35     * The load factor for the hash table.
 36     *
 37     * @serial
 38     */
 39     finalfloat loadFactor;
 40     /**
 41     * The number of times this HashMap has been structurally modified
 42     * Structural modifications are those that change the number of mappings in
 43     * the HashMap or otherwise modify its internal structure (e.g.,
 44     * rehash). This field is used to make iterators on Collection-views of
 45     * the HashMap fail-fast. (See ConcurrentModificationException).
 46     */
 47     transientvolatileint modCount;
 48     /**
 49     * Constructs an empty HashMap with the specified initial
 50     * capacity and load factor.
 51     *
 52     * @param initialCapacity the initial capacity
 53     * @param loadFactor the load factor
 54     * @throws IllegalArgumentException if the initial capacity is negative
 55     * or the load factor is nonpositive
 56     */
 57     publicHashMap(int initialCapacity,float loadFactor){
 58     if(initialCapacity <0)
 59     thrownewIllegalArgumentException("Illegal initial capacity: "+
 60     initialCapacity);
 61     if(initialCapacity > MAXIMUM_CAPACITY)
 62     initialCapacity = MAXIMUM_CAPACITY;
 63     if(loadFactor <=0||Float.isNaN(loadFactor))
 64     thrownewIllegalArgumentException("Illegal load factor: "+
 65     loadFactor);
 66     // Find a power of 2 >= initialCapacity
 67     int capacity =1;
 68     while(capacity < initialCapacity)
 69     capacity <<=1;
 70     this.loadFactor = loadFactor;
 71     threshold =(int)(capacity * loadFactor);
 72     table =newEntry[capacity];
 73     init();
 74     }
 75     /**
 76     * Constructs an empty HashMap with the specified initial
 77     * capacity and the default load factor (0.75).
 78     *
 79     * @param initialCapacity the initial capacity.
 80     * @throws IllegalArgumentException if the initial capacity is negative.
 81     */
 82     publicHashMap(int initialCapacity){
 83     this(initialCapacity, DEFAULT_LOAD_FACTOR);
 84     }
 85     /**
 86     * Constructs an empty HashMap with the default initial capacity
 87     * (16) and the default load factor (0.75).
 88     */
 89     publicHashMap(){
 90     this.loadFactor = DEFAULT_LOAD_FACTOR;
 91     threshold =(int)(DEFAULT_INITIAL_CAPACITY * DEFAULT_LOAD_FACTOR);
 92     table =newEntry[DEFAULT_INITIAL_CAPACITY];
 93     init();
 94     }
 95     /**
 96     * Constructs a new HashMap with the same mappings as the
 97     * specified Map. The HashMap is created with
 98     * default load factor (0.75) and an initial capacity sufficient to
 99     * hold the mappings in the specified Map.
100     *
101     * @param m the map whose mappings are to be placed in this map
102     * @throws NullPointerException if the specified map is null
103     */
104     publicHashMap(Map<?extends K,?extends V> m){
105     this(Math.max((int)(m.size()/ DEFAULT_LOAD_FACTOR)+1,
106     DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR);
107     putAllForCreate(m);
108     }
109     // internal utilities
110     /**
111     * Initialization hook for subclasses. This method is called
112     * in all constructors and pseudo-constructors (clone, readObject)
113     * after HashMap has been initialized but before any entries have
114     * been inserted. (In the absence of this method, readObject would
115     * require explicit knowledge of subclasses.)
116     */
117     void init(){
118     }
119     /**
120     * Applies a supplemental hash function to a given hashCode, which
121     * defends against poor quality hash functions. This is critical
122     * because HashMap uses power-of-two length hash tables, that
123     * otherwise encounter collisions for hashCodes that do not differ
124     * in lower bits. Note: Null keys always map to hash 0, thus index 0.
125     */
126     staticint hash(int h){
127     // This function ensures that hashCodes that differ only by
128     // constant multiples at each bit position have a bounded
129     // number of collisions (approximately 8 at default load factor).
130     h ^=(h >>>20)^(h >>>12);
131     return h ^(h >>>7)^(h >>>4);
132     }
133     /**
134     * Returns index for hash code h.
135     */
136     staticint indexFor(int h,int length){
137     return h &(length-1);
138     }
139     /**
140     * Returns the number of key-value mappings in this map.
141     *
142     * @return the number of key-value mappings in this map
143     */
144     publicint size(){
145     return size;
146     }
147     /**
148     * Returns true if this map contains no key-value mappings.
149     *
150     * @return true if this map contains no key-value mappings
151     */
152     publicboolean isEmpty(){
153     return size ==0;
154     }
155     /**
156     * Returns the value to which the specified key is mapped,
157     * or {@code null} if this map contains no mapping for the key.
158     *
159     * 
More formally, if this map contains a mapping from a key
160     * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
161     * key.equals(k))}, then this method returns {@code v}; otherwise
162     * it returns {@code null}. (There can be at most one such mapping.)
163     *
164     * 
A return value of {@code null} does not necessarily
165     * indicate that the map contains no mapping for the key; it's also
166     * possible that the map explicitly maps the key to {@code null}.
167     * The {@link #containsKey containsKey} operation may be used to
168     * distinguish these two cases.
169     *
170     * @see #put(Object, Object)
171     */
172     public V get(Object key){
173     if(key ==null)
174     return getForNullKey();
175     int hash = hash(key.hashCode());
176     for(Entry e = table[indexFor(hash, table.length)];
177     e !=null;
178     e = e.next){
179     Object k;
180     if(e.hash == hash &&((k = e.key)== key || key.equals(k)))
181     return e.value;
182     }
183     returnnull;
184     }
185     /**
186     * Offloaded version of get() to look up null keys. Null keys map
187     * to index 0. This null case is split out into separate methods
188     * for the sake of performance in the two most commonly used
189     * operations (get and put), but incorporated with conditionals in
190     * others.
191     */
192     private V getForNullKey(){
193     for(Entry e = table[0]; e !=null; e = e.next){
194     if(e.key ==null)
195     return e.value;
196     }
197     returnnull;
198     }
199     /**
200     * Returns true if this map contains a mapping for the
201     * specified key.
202     *
203     * @param key The key whose presence in this map is to be tested
204     * @return true if this map contains a mapping for the specified
205     * key.
206     */
207     publicboolean containsKey(Object key){
208     return getEntry(key)!=null;
209     }
210     /**
211     * Returns the entry associated with the specified key in the
212     * HashMap. Returns null if the HashMap contains no mapping
213     * for the key.
214     */
215     finalEntry getEntry(Object key){
216     int hash =(key ==null)?0: hash(key.hashCode());
217     for(Entry e = table[indexFor(hash, table.length)];
218     e !=null;
219     e = e.next){
220     Object k;
221     if(e.hash == hash &&
222     ((k = e.key)== key ||(key !=null&& key.equals(k))))
223     return e;
224     }
225     returnnull;
226     }
227     /**
228     * Associates the specified value with the specified key in this map.
229     * If the map previously contained a mapping for the key, the old
230     * value is replaced.
231     *
232     * @param key key with which the specified value is to be associated
233     * @param value value to be associated with the specified key
234     * @return the previous value associated with key, or
235     * null if there was no mapping for key.
236     * (A null return can also indicate that the map
237     * previously associated null with key.)
238     */
239     public V put(K key, V value){
240     if(key ==null)
241     return putForNullKey(value);
242     int hash = hash(key.hashCode());
243     int i = indexFor(hash, table.length);
244     for(Entry e = table[i]; e !=null; e = e.next){
245     Object k;
246     if(e.hash == hash &&((k = e.key)== key || key.equals(k))){
247     V oldValue = e.value;
248     e.value = value;
249     e.recordAccess(this);
250     return oldValue;
251     }
252     }
253     modCount++;
254     addEntry(hash, key, value, i);
255     returnnull;
256     }
257     /**
258     * Offloaded version of put for null keys
259     */
260     private V putForNullKey(V value){
261     for(Entry e = table[0]; e !=null; e = e.next){
262     if(e.key ==null){
263     V oldValue = e.value;
264     e.value = value;
265     e.recordAccess(this);
266     return oldValue;
267     }
268     }
269     modCount++;
270     addEntry(0,null, value,0);
271     returnnull;
272     }
273     // These methods are used when serializing HashSets
274     int capacity(){return table.length;}
275     float loadFactor(){return loadFactor;}
276     }
277 
278 HashTable类
279 
280     publicclassHashtable
281     extendsDictionary
282     implementsMap,Cloneable, java.io.Serializable{
283     /**
284     * The hash table data.
285     */
286     privatetransientEntry[] table;
287     /**
288     * The total number of entries in the hash table.
289     */
290     privatetransientint count;
291     /**
292     * The table is rehashed when its size exceeds this threshold. (The
293     * value of this field is (int)(capacity * loadFactor).)
294     *
295     * @serial
296     */
297     privateint threshold;
298     /**
299     * The load factor for the hashtable.
300     *
301     * @serial
302     */
303     privatefloat loadFactor;
304     /**
305     * The number of times this Hashtable has been structurally modified
306     * Structural modifications are those that change the number of entries in
307     * the Hashtable or otherwise modify its internal structure (e.g.,
308     * rehash). This field is used to make iterators on Collection-views of
309     * the Hashtable fail-fast. (See ConcurrentModificationException).
310     */
311     privatetransientint modCount =0;
312     /** use serialVersionUID from JDK 1.0.2 for interoperability */
313     privatestaticfinallong serialVersionUID =1421746759512286392L;
314     /**
315     * Constructs a new, empty hashtable with the specified initial
316     * capacity and the specified load factor.
317     *
318     * @param initialCapacity the initial capacity of the hashtable.
319     * @param loadFactor the load factor of the hashtable.
320     * @exception IllegalArgumentException if the initial capacity is less
321     * than zero, or if the load factor is nonpositive.
322     */
323     publicHashtable(int initialCapacity,float loadFactor){
324     if(initialCapacity <0)
325     thrownewIllegalArgumentException("Illegal Capacity: "+
326     initialCapacity);
327     if(loadFactor <=0||Float.isNaN(loadFactor))
328     thrownewIllegalArgumentException("Illegal Load: "+loadFactor);
329     if(initialCapacity==0)
330     initialCapacity =1;
331     this.loadFactor = loadFactor;
332     table =newEntry[initialCapacity];
333     threshold =(int)(initialCapacity * loadFactor);
334     }
335     /**
336     * Constructs a new, empty hashtable with the specified initial capacity
337     * and default load factor (0.75).
338     *
339     * @param initialCapacity the initial capacity of the hashtable.
340     * @exception IllegalArgumentException if the initial capacity is less
341     * than zero.
342     */
343     publicHashtable(int initialCapacity){
344     this(initialCapacity,0.75f);
345     }
346     /**
347     * Constructs a new, empty hashtable with a default initial capacity (11)
348     * and load factor (0.75).
349     */
350     publicHashtable(){
351     this(11,0.75f);
352     }
353     /**
354     * Constructs a new hashtable with the same mappings as the given
355     * Map. The hashtable is created with an initial capacity sufficient to
356     * hold the mappings in the given Map and a default load factor (0.75).
357     *
358     * @param t the map whose mappings are to be placed in this map.
359     * @throws NullPointerException if the specified map is null.
360     * @since 1.2
361     */
362     publicHashtable(Map<?extends K,?extends V> t){
363     this(Math.max(2*t.size(),11),0.75f);
364     putAll(t);
365     }
366     /**
367     * Returns the number of keys in this hashtable.
368     *
369     * @return the number of keys in this hashtable.
370     */
371     publicsynchronizedint size(){
372     return count;
373     }
374     /**
375     * Tests if this hashtable maps no keys to values.
376     *
377     * @return true if this hashtable maps no keys to values;
378     * false otherwise.
379     */
380     publicsynchronizedboolean isEmpty(){
381     return count ==0;
382     }
383     /**
384     * Returns an enumeration of the keys in this hashtable.
385     *
386     * @return an enumeration of the keys in this hashtable.
387     * @see Enumeration
388     * @see #elements()
389     * @see #keySet()
390     * @see Map
391     */
392     publicsynchronizedEnumeration keys(){
393     returnthis.getEnumeration(KEYS);
394     }

1.     HashTable的方法是同步的，HashMap不能同步，所以在线程多的场合要使用HashTable；
   
2. HashTable不允许空值（key和value都不可以为null），hashmap则可以为null
3. HashTable有一个contains()的方法，功能和containsValue()一样
4. HashTable使用Enumeration，而HashMap使用Iterator
5. HashTabe中的hash数组默认大小为11，增长方式为old*2+1，hashmap的hash为16，是2的指数倍
6. 哈希值的使用不同，HashTable直接使用对象hashcode，而HashMap会重新计算hash值