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Vector簡介

Vector也是基于數組實現的，是一個動態數組，其容量能自動增長。

Vector是JDK1.0引入了，它的很多實現方法都加入了同步語句，因此是線程安全的(其實也只是相對安全，有些時候還是要加入同步語句來保證線程的安全)，可以用于多線程環境。

Vector沒有實現Serializable接口，因此它不支持序列化，實現了Cloneable接口，能被克隆，實現了RandomAccess接口，支持快速隨機訪問。

Vector源碼剖析

Vector的源碼如下(加入了比較詳細的注釋)：

package?java.util;????
???
public?class?Vector????
????extends?AbstractList????
????implements?List,?RandomAccess,?Cloneable,?java.io.Serializable????
{????
????//?保存Vector中數據的數組????
????protected?Object[]?elementData;????
????//?實際數據的數量????
????protected?int?elementCount;????
????//?容量增長系數????
????protected?int?capacityIncrement;????
????//?Vector的序列版本號????
????private?static?final?long?serialVersionUID?=?-2767605614048989439L;????
????// Vector構造函數。默認容量是10。????
????public?Vector()?{????
????????this(10);????
????}????
????//?指定Vector容量大小的構造函數????
????public?Vector(int?initialCapacity)?{????
????????this(initialCapacity,?0);????
????}????
????//?指定Vector"容量大小"和"增長系數"的構造函數????
????public?Vector(int?initialCapacity,?int?capacityIncrement)?{????
????????super();????if?(initialCapacity?????????????throw?new?IllegalArgumentException("Illegal?Capacity:?"+????
???????????????????????????????????????????????initialCapacity);????
????????//?新建一個數組，數組容量是initialCapacity????
????????this.elementData?=?new?Object[initialCapacity];????
????????//?設置容量增長系數????
????????this.capacityIncrement?=?capacityIncrement;????
????}????
????//?指定集合的Vector構造函數。????
????public?Vector(Collection?extends?E>?c)?{????
????????//?獲取“集合(c)”的數組，并將其賦值給elementData????
????????elementData?=?c.toArray();????
????????//?設置數組長度????
????????elementCount?=?elementData.length;????
????????//?c.toArray?might?(incorrectly)?not?return?Object[]?(see?6260652)????if?(elementData.getClass()?!=?Object[].class)????
????????????elementData?=?Arrays.copyOf(elementData,?elementCount,?Object[].class);????
????}????
????//?將數組Vector的全部元素都拷貝到數組anArray中????
????public?synchronized?void?copyInto(Object[]?anArray)?{????
????????System.arraycopy(elementData,?0,?anArray,?0,?elementCount);????
????}????
????//?將當前容量值設為?=實際元素個數????
????public?synchronized?void?trimToSize()?{????
????????modCount++;????
????????int?oldCapacity?=?elementData.length;????if?(elementCount?????????????elementData?=?Arrays.copyOf(elementData,?elementCount);????
????????}????
????}????
????//?確認“Vector容量”的幫助函數????
????private?void?ensureCapacityHelper(int?minCapacity)?{????
????????int?oldCapacity?=?elementData.length;????
????????//?當Vector的容量不足以容納當前的全部元素，增加容量大小。????
????????//?若?容量增量系數>0(即capacityIncrement>0)，則將容量增大當capacityIncrement????
????????//?否則，將容量增大一倍。????if?(minCapacity?>?oldCapacity)?{????
????????????Object[]?oldData?=?elementData;????
????????????int?newCapacity?=?(capacityIncrement?>?0)??????
????????????????(oldCapacity?+?capacityIncrement)?:?(oldCapacity?*?2);????if?(newCapacity?????????????????newCapacity?=?minCapacity;????
????????????}????
????????????elementData?=?Arrays.copyOf(elementData,?newCapacity);????
????????}????
????}????
????//?確定Vector的容量。????
????public?synchronized?void?ensureCapacity(int?minCapacity)?{????
????????//?將Vector的改變統計數+1????
????????modCount++;????
????????ensureCapacityHelper(minCapacity);????
????}????
????//?設置容量值為?newSize????
????public?synchronized?void?setSize(int?newSize)?{????
????????modCount++;????if?(newSize?>?elementCount)?{????
????????????//?若?"newSize?大于?Vector容量"，則調整Vector的大小。????
????????????ensureCapacityHelper(newSize);????
????????}?else?{????
????????????//?若?"newSize?小于/等于?Vector容量"，則將newSize位置開始的元素都設置為null????for?(int?i?=?newSize?;?i?????????????????elementData[i]?=?null;????
????????????}????
????????}????
????????elementCount?=?newSize;????
????}????
????//?返回“Vector的總的容量”????
????public?synchronized?int?capacity()?{????return?elementData.length;????
????}????
????//?返回“Vector的實際大小”，即Vector中元素個數????
????public?synchronized?int?size()?{????return?elementCount;????
????}????
????//?判斷Vector是否為空????
????public?synchronized?boolean?isEmpty()?{????return?elementCount?==?0;????
????}????
????//?返回“Vector中全部元素對應的Enumeration”????
????public?Enumeration?elements()?{????
????????//?通過匿名類實現Enumeration????return?new?Enumeration()?{????
????????????int?count?=?0;????
????????????//?是否存在下一個元素????
????????????public?boolean?hasMoreElements()?{????return?count?????????????}????
????????????//?獲取下一個元素????
????????????public?E?nextElement()?{????
????????????????synchronized?(Vector.this)?{????if?(count?????????????????????????return?(E)elementData[count++];????
????????????????????}????
????????????????}????
????????????????throw?new?NoSuchElementException("Vector?Enumeration");????
????????????}????
????????};????
????}????
????//?返回Vector中是否包含對象(o)????
????public?boolean?contains(Object?o)?{????return?indexOf(o,?0)?>=?0;????
????}????
????//?從index位置開始向后查找元素(o)。????
????//?若找到，則返回元素的索引值；否則，返回-1 ???
????public?synchronized?int?indexOf(Object?o,?int?index)?{????if?(o?==?null)?{????
????????????//?若查找元素為null，則正向找出null元素，并返回它對應的序號????for?(int?i?=?index?;?i?????????????if?(elementData[i]==null)????return?i;????
????????}?else?{????
????????????//?若查找元素不為null，則正向找出該元素，并返回它對應的序號????for?(int?i?=?index?;?i?????????????if?(o.equals(elementData[i]))????return?i;????
????????}????return?-1;????
????}????
????//?查找并返回元素(o)在Vector中的索引值????
????public?int?indexOf(Object?o)?{????return?indexOf(o,?0);????
????}????
????//?從后向前查找元素(o)。并返回元素的索引????
????public?synchronized?int?lastIndexOf(Object?o)?{????return?lastIndexOf(o,?elementCount-1);????
????}????
????//?從后向前查找元素(o)。開始位置是從前向后的第index個數；????
????//?若找到，則返回元素的“索引值”；否則，返回-1。????
????public?synchronized?int?lastIndexOf(Object?o,?int?index)?{????if?(index?>=?elementCount)????
????????????throw?new?IndexOutOfBoundsException(index?+?"?>=?"+?elementCount);????if?(o?==?null)?{????
????????????//?若查找元素為null，則反向找出null元素，并返回它對應的序號????for?(int?i?=?index;?i?>=?0;?i--)????if?(elementData[i]==null)????return?i;????
????????}?else?{????
????????????//?若查找元素不為null，則反向找出該元素，并返回它對應的序號????for?(int?i?=?index;?i?>=?0;?i--)????if?(o.equals(elementData[i]))????return?i;????
????????}????return?-1;????
????}????
????//?返回Vector中index位置的元素。????
????//?若index月結，則拋出異常????
????public?synchronized?E?elementAt(int?index)?{????if?(index?>=?elementCount)?{????
????????????throw?new?ArrayIndexOutOfBoundsException(index?+?"?>=?"?+?elementCount);????
????????}????return?(E)elementData[index];????
????}????
????//?獲取Vector中的第一個元素。????
????//?若失敗，則拋出異常！????
????public?synchronized?E?firstElement()?{????if?(elementCount?==?0)?{????
????????????throw?new?NoSuchElementException();????
????????}????return?(E)elementData[0];????
????}????
????//?獲取Vector中的最后一個元素。????
????//?若失敗，則拋出異常！????
????public?synchronized?E?lastElement()?{????if?(elementCount?==?0)?{????
????????????throw?new?NoSuchElementException();????
????????}????return?(E)elementData[elementCount?-?1];????
????}????
????//?設置index位置的元素值為obj????
????public?synchronized?void?setElementAt(E?obj,?int?index)?{????if?(index?>=?elementCount)?{????
????????????throw?new?ArrayIndexOutOfBoundsException(index?+?"?>=?"?+????
?????????????????????????????????elementCount);????
????????}????
????????elementData[index]?=?obj;????
????}????
????//?刪除index位置的元素????
????public?synchronized?void?removeElementAt(int?index)?{????
????????modCount++;????if?(index?>=?elementCount)?{????
????????????throw?new?ArrayIndexOutOfBoundsException(index?+?"?>=?"?+????
?????????????????????????????????elementCount);????
????????}?else?if?(index?????????????throw?new?ArrayIndexOutOfBoundsException(index);????
????????}????
????????int?j?=?elementCount?-?index?-?1;????if?(j?>?0)?{????
????????????System.arraycopy(elementData,?index?+?1,?elementData,?index,?j);????
????????}????
????????elementCount--;????
????????elementData[elementCount]?=?null;?/*?to?let?gc?do?its?work?*/???
????}????
????//?在index位置處插入元素(obj)????
????public?synchronized?void?insertElementAt(E?obj,?int?index)?{????
????????modCount++;????if?(index?>?elementCount)?{????
????????????throw?new?ArrayIndexOutOfBoundsException(index????
?????????????????????????????????+?"?>?"?+?elementCount);????
????????}????
????????ensureCapacityHelper(elementCount?+?1);????
????????System.arraycopy(elementData,?index,?elementData,?index?+?1,?elementCount?-?index);????
????????elementData[index]?=?obj;????
????????elementCount++;????
????}????
????//?將“元素obj”添加到Vector末尾????
????public?synchronized?void?addElement(E?obj)?{????
????????modCount++;????
????????ensureCapacityHelper(elementCount?+?1);????
????????elementData[elementCount++]?=?obj;????
????}????
????//?在Vector中查找并刪除元素obj。????
????//?成功的話，返回true；否則，返回false。????
????public?synchronized?boolean?removeElement(Object?obj)?{????
????????modCount++;????
????????int?i?=?indexOf(obj);????if?(i?>=?0)?{????
????????????removeElementAt(i);????return?true;????
????????}????return?false;????
????}????
????//?刪除Vector中的全部元素????
????public?synchronized?void?removeAllElements()?{????
????????modCount++;????
????????//?將Vector中的全部元素設為null????for?(int?i?=?0;?i?????????????elementData[i]?=?null;????
????????elementCount?=?0;????
????}????
????//?克隆函數????
????public?synchronized?Object?clone()?{????
????????try?{????
????????????Vector?v?=?(Vector)?super.clone();????
????????????//?將當前Vector的全部元素拷貝到v中????
????????????v.elementData?=?Arrays.copyOf(elementData,?elementCount);????
????????????v.modCount?=?0;????return?v;????
????????}?catch?(CloneNotSupportedException?e)?{????
????????????//?this?shouldn't?happen,?since?we?are?Cloneable????
????????????throw?new?InternalError();????
????????}????
????}????
????//?返回Object數組????
????public?synchronized?Object[]?toArray()?{????
????????return?Arrays.copyOf(elementData,?elementCount);????
????}????
????//?返回Vector的模板數組。所謂模板數組，即可以將T設為任意的數據類型????
????public?synchronized??T[]?toArray(T[]?a)?{????
????????//?若數組a的大小?< Vector的元素個數；????
????????//?則新建一個T[]數組，數組大小是“Vector的元素個數”，并將“Vector”全部拷貝到新數組中????
????????if?(a.length?????????????return?(T[])?Arrays.copyOf(elementData,?elementCount,?a.getClass());????
????????//?若數組a的大小?>= Vector的元素個數；????
????????//?則將Vector的全部元素都拷貝到數組a中。????
????System.arraycopy(elementData,?0,?a,?0,?elementCount);????
????????if?(a.length?>?elementCount)????
????????????a[elementCount]?=?null;????
????????return?a;????
????}????
????//?獲取index位置的元素????
????public?synchronized?E?get(int?index)?{????
????????if?(index?>=?elementCount)????
????????????throw?new?ArrayIndexOutOfBoundsException(index);????
????????return?(E)elementData[index];????
????}????
????//?設置index位置的值為element。并返回index位置的原始值????
????public?synchronized?E?set(int?index,?E?element)?{????
????????if?(index?>=?elementCount)????
????????????throw?new?ArrayIndexOutOfBoundsException(index);????
????????Object?oldValue?=?elementData[index];????
????????elementData[index]?=?element;????
????????return?(E)oldValue;????
????}????
????//?將“元素e”添加到Vector最后。????
????public?synchronized?boolean?add(E?e)?{????
????????modCount++;????
????????ensureCapacityHelper(elementCount?+?1);????
????????elementData[elementCount++]?=?e;????
????????return?true;????
????}????
????//?刪除Vector中的元素o????
????public?boolean?remove(Object?o)?{????
????????return?removeElement(o);????
????}????
????//?在index位置添加元素element????
????public?void?add(int?index,?E?element)?{????
????????insertElementAt(element,?index);????
????}????
????//?刪除index位置的元素，并返回index位置的原始值????
????public?synchronized?E?remove(int?index)?{????
????????modCount++;????
????????if?(index?>=?elementCount)????
????????????throw?new?ArrayIndexOutOfBoundsException(index);????
????????Object?oldValue?=?elementData[index];????
????????int?numMoved?=?elementCount?-?index?-?1;????
????????if?(numMoved?>?0)????
????????????System.arraycopy(elementData,?index+1,?elementData,?index,????
?????????????????????numMoved);????
????????elementData[--elementCount]?=?null;?//?Let?gc?do?its?work????
????????return?(E)oldValue;????
????}????
????//?清空Vector????
????public?void?clear()?{????
????????removeAllElements();????
????}????
????//?返回Vector是否包含集合c????
????public?synchronized?boolean?containsAll(Collection>?c)?{????
????????return?super.containsAll(c);????
????}????
????//?將集合c添加到Vector中????
????public?synchronized?boolean?addAll(Collection?extends?E>?c)?{????
????????modCount++;????
????????Object[]?a?=?c.toArray();????
????????int?numNew?=?a.length;????
????????ensureCapacityHelper(elementCount?+?numNew);????
????????//?將集合c的全部元素拷貝到數組elementData中????
????????System.arraycopy(a,?0,?elementData,?elementCount,?numNew);????
????????elementCount?+=?numNew;????
????????return?numNew?!=?0;????
????}????
????//?刪除集合c的全部元素????
????public?synchronized?boolean?removeAll(Collection>?c)?{????
????????return?super.removeAll(c);????
????}????
????//?刪除“非集合c中的元素”????
????public?synchronized?boolean?retainAll(Collection>?c)??{????
????????return?super.retainAll(c);????
????}????
????//?從index位置開始，將集合c添加到Vector中????
????public?synchronized?boolean?addAll(int?index,?Collection?extends?E>?c)?{????
????????modCount++;????
????????if?(index??elementCount)????
????????????throw?new?ArrayIndexOutOfBoundsException(index);????
????????Object[]?a?=?c.toArray();????
????????int?numNew?=?a.length;????
????????ensureCapacityHelper(elementCount?+?numNew);????
????????int?numMoved?=?elementCount?-?index;????
????????if?(numMoved?>?0)????
????????System.arraycopy(elementData,?index,?elementData,?index?+?numNew,?numMoved);????
????????System.arraycopy(a,?0,?elementData,?index,?numNew);????
????????elementCount?+=?numNew;????
????????return?numNew?!=?0;????
????}????
????//?返回兩個對象是否相等????
????public?synchronized?boolean?equals(Object?o)?{????
????????return?super.equals(o);????
????}????
????//?計算哈希值????
????public?synchronized?int?hashCode()?{????
????????return?super.hashCode();????
????}????
????//?調用父類的toString()????
????public?synchronized?String?toString()?{????
????????return?super.toString();????
????}????
????//?獲取Vector中fromIndex(包括)到toIndex(不包括)的子集????
????public?synchronized?List?subList(int?fromIndex,?int?toIndex)?{????
????????return?Collections.synchronizedList(super.subList(fromIndex,?toIndex),?this);????
????}????
????//?刪除Vector中fromIndex到toIndex的元素????
????protected?synchronized?void?removeRange(int?fromIndex,?int?toIndex)?{????
????????modCount++;????
????????int?numMoved?=?elementCount?-?toIndex;????
????????System.arraycopy(elementData,?toIndex,?elementData,?fromIndex,????
?????????????????????????numMoved);????
????????//?Let?gc?do?its?work????
????????int?newElementCount?=?elementCount?-?(toIndex-fromIndex);????
????????while?(elementCount?!=?newElementCount)????
????????????elementData[--elementCount]?=?null;????
????}????
????//?java.io.Serializable的寫入函數????
????private?synchronized?void?writeObject(java.io.ObjectOutputStream?s)????
????????throws?java.io.IOException?{????
????????s.defaultWriteObject();????
????}????
}???

幾點總結

Vector的源碼實現總體與ArrayList類似，關于Vector的源碼，給出如下幾點總結：

1、Vector有四個不同的構造方法。無參構造方法的容量為默認值10，僅包含容量的構造方法則將容量增長量(從源碼中可以看出容量增長量的作用，第二點也會對容量增長量詳細說)明置為0。

2、注意擴充容量的方法ensureCapacityHelper。與ArrayList相同，Vector在每次增加元素(可能是1個，也可能是一組)時，都要調用該方法來確保足夠的容量。當容量不足以容納當前的元素個數時，就先看構造方法中傳入的容量增長量參數CapacityIncrement是否為0，如果不為0，就設置新的容量為就容量加上容量增長量，如果為0，就設置新的容量為舊的容量的2倍，如果設置后的新容量還不夠，則直接新容量設置為傳入的參數(也就是所需的容量)，而后同樣用Arrays.copyof()方法將元素拷貝到新的數組。

3、很多方法都加入了synchronized同步語句，來保證線程安全。

4、同樣在查找給定元素索引值等的方法中，源碼都將該元素的值分為null和不為null兩種情況處理，Vector中也允許元素為null。

5、其他很多地方都與ArrayList實現大同小異，Vector現在已經基本不再使用。

戳這兒

總結

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