一、Vector簡介：

（1）Vector可以實現可增長的對象數組。與數組一樣，可以使用整數索引進行訪問的組件。不過，Vector的大小是可以增加或者減小的，以便適應創建Vector后進行添加或者刪除操作。

（2）同時Vector是線程安全的！底層使用的是synchronized進行加鎖。

public class Vector<E>extends AbstractList<E>implements List<E>, RandomAccess, Cloneable, java.io.Serializable

1、Vector實現List接口，繼承AbstractList類，所以我們可以將其看做隊列，支持相關的添加、刪除、修改、遍歷等功能。

Vector實現RandmoAccess接口，即提供了隨機訪問功能，提供提供快速訪問功能。在Vector我們可以直接訪問元素。

Vector 實現了Cloneable接口，支持clone()方法，可以被克隆。

Vector實現了Serializable接口，因此可以進行序列化。

2、成員變量方面，Vector提供了elementData , elementCount， capacityIncrement三個成員變量。其中

（1）elementData ："Object[]類型的數組"，它保存了Vector中的元素，是一個動態數組，可以隨著元素的增加而動態的增長，（具體增長方式在ensureCapacity方法中）。如果在初始化Vector時沒有指定容器大小，則使用默認大小為10。

（2）elementCount：Vector 對象中的元素個數。

（3）capacityIncrement：向量的大小大于其容量時，容量自動增加的量。如果在創建Vector時，指定了capacityIncrement的大小，則每次當Vector中動態數組容量增加時，增加的大小都是capacityIncrement。如果容量的增量小于等于零，則每次需要增大容量時，向量的容量將增大一倍。

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二、Vector遍歷：

//第一種：通過下標進行隨機訪問 for(int i = 0 ; i < vec.size() ; i++){value = vec.get(i);}//第二種：迭代器： Iterator it = vec.iterator();while(it.hasNext()){value = it.next();//do something}//第三種：for循環 for(Integer value:vec){//do something}//第四種：Enumeration循環: Vector vec = new Vector<>();Enumeration enu = vec.elements();while (enu.hasMoreElements()) {value = (Integer)enu.nextElement();}

Vector示例代碼：

public class Hello {public static void main(String[] args) {Vector vec = new Vector();// 添加vec.add("1");vec.add("2");vec.add("3");vec.add("4");vec.add("5");// 替換vec.set(0, "100");vec.add(2, "300");System.out.println("vec:" + vec);System.out.println("vec.indexOf(100):" + vec.indexOf("100"));System.out.println("vec.lastIndexOf(100):" + vec.lastIndexOf("100"));System.out.println("vec.firstElement():" + vec.firstElement());System.out.println("vec.elementAt(2):" + vec.elementAt(2));System.out.println("vec.lastElement():" + vec.lastElement());System.out.println("size:" + vec.size());System.out.println("capacity:" + vec.capacity());System.out.println("vec 2 to 4:" + vec.subList(1, 4));Enumeration enu = vec.elements();while (enu.hasMoreElements()) {System.out.println("nextElement():" + enu.nextElement());Vector retainVec = new Vector();retainVec.add("100");retainVec.add("300");System.out.println("vec.retain():" + vec.retainAll(retainVec));System.out.println("vec:" + vec);String[] arr = (String[]) vec.toArray(new String[0]);for (String str : arr)System.out.println("str:" + str);vec.clear();vec.removeAllElements();System.out.println("vec.isEmpty():" + vec.isEmpty());}} }

輸出結果：

vec:[100, 2, 300, 3, 4, 5] vec.indexOf(100):0 vec.lastIndexOf(100):0 vec.firstElement():100 vec.elementAt(2):300 vec.lastElement():5 size:6 capacity:10 vec 2 to 4:[2, 300, 3] nextElement():100 vec.retain():true vec:[100, 300] str:100 str:300 vec.isEmpty():true

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三、源碼解析：

1、add（E e）：添加元素

add(E e)：將指定元素添加到此向量的末尾。

public synchronized boolean add(E e) {modCount++; ensureCapacityHelper(elementCount + 1); //確認容器大小，如果超過容量則擴容操作elementData[elementCount++] = e; //將e元素添加至末尾return true;}

?這個方法相對而言比較簡單，具體過程就是先確認容器的大小，看是否需要進行擴容操作，然后將E元素添加到此向量的末尾。

private void ensureCapacityHelper(int minCapacity) {if (minCapacity - elementData.length > 0)grow(minCapacity);}/*** 進行擴容操作* 如果此向量的當前容量小于minCapacity，則通過將其內部數組替換為一個較大的數組倆增加其容量。* 新數據數組的大小姜維原來的大小 + capacityIncrement，* 除非 capacityIncrement 的值小于等于零，在后一種情況下，新的容量將為原來容量的兩倍，不過，如果此大小仍然小于 minCapacity，則新容量將為 minCapacity。*/private void grow(int minCapacity) {int oldCapacity = elementData.length; //當前容器大小/** 新容器大小* 若容量增量系數(capacityIncrement) > 0，則將容器大小增加到capacityIncrement* 否則將容量增加一倍*/int newCapacity = oldCapacity + ((capacityIncrement > 0) ?capacityIncrement : oldCapacity);if (newCapacity - minCapacity < 0)newCapacity = minCapacity;if (newCapacity - MAX_ARRAY_SIZE > 0)newCapacity = hugeCapacity(minCapacity);elementData = Arrays.copyOf(elementData, newCapacity);}/*** 判斷是否超出最大范圍* MAX_ARRAY_SIZE：private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;*/private static int hugeCapacity(int minCapacity) {if (minCapacity < 0)throw new OutOfMemoryError();return (minCapacity > MAX_ARRAY_SIZE) ? Integer.MAX_VALUE : MAX_ARRAY_SIZE;}

對于Vector整個的擴容過程，就是根據capacityIncrement確認擴容大小的，若capacityIncrement <= 0 則擴大一倍，否則擴大至capacityIncrement 。當然這個容量的最大范圍為Integer.MAX_VALUE即，2^32 - 1，所以Vector并不是可以無限擴充的。

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2、remove(Object o)：

/*** 從Vector容器中移除指定元素E*/public boolean remove(Object o) {return removeElement(o);}public synchronized boolean removeElement(Object obj) {modCount++;int i = indexOf(obj); //計算obj在Vector容器中位置if (i >= 0) {removeElementAt(i); //移除return true;}return false;}public synchronized void removeElementAt(int index) {modCount++; //修改次數+1if (index >= elementCount) { //刪除位置大于容器有效大小throw new ArrayIndexOutOfBoundsException(index + " >= " + elementCount);}else if (index < 0) { //位置小于 < 0throw new ArrayIndexOutOfBoundsException(index);}int j = elementCount - index - 1;if (j > 0) { //從指定源數組中復制一個數組，復制從指定的位置開始，到目標數組的指定位置結束。//也就是數組元素從j位置往前移System.arraycopy(elementData, index + 1, elementData, index, j);}elementCount--; //容器中有效組件個數 - 1elementData[elementCount] = null; //將向量的末尾位置設置為null}

?因為Vector底層是使用數組實現的，所以它的操作都是對數組進行操作，只不過其是可以隨著元素的增加而動態的改變容量大小，其實現方法是是使用Arrays.copyOf方法將舊數據拷貝到一個新的大容量數組中。Vector的整個內部實現都比較簡單，這里就不在重述了。

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3、Vector 其他方法源代碼：

public class Vector<E> extends AbstractList<E>implements List<E>, RandomAccess, Cloneable, java.io.Serializable {protected Object[] elementData;//對象數組，來存放數據protected int elementCount; //當前的數據數目protected int capacityIncrement; //容量增長private static final long serialVersionUID = -2767605614048989439L; //序列號//構造函數矢量隊列初始化大小和增長大小public Vector(int initialCapacity, int capacityIncrement) {super();if (initialCapacity < 0)throw new IllegalArgumentException("Illegal Capacity: "+initialCapacity);this.elementData = new Object[initialCapacity];this.capacityIncrement = capacityIncrement;}//構造函數初始化大小public Vector(int initialCapacity) {this(initialCapacity, 0);}//構造函數默認初始化大小10public Vector() {this(10);}//帶有集合參數的構造函數public Vector(Collection<? extends E> c) {elementData = c.toArray();elementCount = elementData.length; // c.toArray might (incorrectly) not return Object[] (see 6260652)if (elementData.getClass() != Object[].class)elementData = Arrays.copyOf(elementData, elementCount, Object[].class);}//線程安全的對象數組拷貝public synchronized void copyInto(Object[] anArray) {System.arraycopy(elementData, 0, anArray, 0, elementCount);}//調整容量大小適合當前矢量隊列的大小public synchronized void trimToSize() {modCount++;int oldCapacity = elementData.length;if (elementCount < oldCapacity) {elementData = Arrays.copyOf(elementData, elementCount);}}//增加矢量隊列的容量大小public synchronized void ensureCapacity(int minCapacity) {if (minCapacity > 0) {modCount++;ensureCapacityHelper(minCapacity);}}private void ensureCapacityHelper(int minCapacity) { // overflow-conscious codeif (minCapacity - elementData.length > 0)grow(minCapacity);}private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;private void grow(int minCapacity) { // overflow-conscious codeint oldCapacity = elementData.length;int newCapacity = oldCapacity + ((capacityIncrement > 0) ?capacityIncrement : oldCapacity);if (newCapacity - minCapacity < 0)newCapacity = minCapacity;if (newCapacity - MAX_ARRAY_SIZE > 0)newCapacity = hugeCapacity(minCapacity);elementData = Arrays.copyOf(elementData, newCapacity);}private static int hugeCapacity(int minCapacity) {if (minCapacity < 0) // overflowthrow new OutOfMemoryError();return (minCapacity > MAX_ARRAY_SIZE) ?Integer.MAX_VALUE :MAX_ARRAY_SIZE;}//調整大小，如果超出了就刪掉多余的對象public synchronized void setSize(int newSize) {modCount++;if (newSize > elementCount) {ensureCapacityHelper(newSize);} else {for (int i = newSize ; i < elementCount ; i++) {elementData[i] = null;}}elementCount = newSize;}//矢量對象的容量public synchronized int capacity() {return elementData.length;}//矢量隊列的大小public synchronized int size() {return elementCount;}//是否為空public synchronized boolean isEmpty() {return elementCount == 0;}//生成Enumeration對象，進行遍歷public Enumeration<E> elements() {return new Enumeration<E>() {int count = 0;public boolean hasMoreElements() {return count < elementCount;}public E nextElement() {synchronized (Vector.this) {if (count < elementCount) {return elementData(count++);}}throw new NoSuchElementException("Vector Enumeration");}};}//判斷是否包含某個對象public boolean contains(Object o) {return indexOf(o, 0) >= 0;}//返回某個對象的下標public int indexOf(Object o) {return indexOf(o, 0);}public synchronized int indexOf(Object o, int index) {if (o == null) {for (int i = index ; i < elementCount ; i++)if (elementData[i]==null)return i;} else {for (int i = index ; i < elementCount ; i++)if (o.equals(elementData[i]))return i;}return -1;}//最后出現的對象的坐標public synchronized int lastIndexOf(Object o) {return lastIndexOf(o, elementCount-1);}public synchronized int lastIndexOf(Object o, int index) {if (index >= elementCount)throw new IndexOutOfBoundsException(index + " >= "+ elementCount);if (o == null) {for (int i = index; i >= 0; i--)if (elementData[i]==null)return i;} else {for (int i = index; i >= 0; i--)if (o.equals(elementData[i]))return i;}return -1;}//返回某個坐標的節點public synchronized E elementAt(int index) {if (index >= elementCount) {throw new ArrayIndexOutOfBoundsException(index + " >= " + elementCount);}return elementData(index);}//第一個元素public synchronized E firstElement() {if (elementCount == 0) {throw new NoSuchElementException();}return elementData(0);}//最后一個元素public synchronized E lastElement() {if (elementCount == 0) {throw new NoSuchElementException();}return elementData(elementCount - 1);}//對下標為index的元素替換為objpublic synchronized void setElementAt(E obj, int index) {if (index >= elementCount) {throw new ArrayIndexOutOfBoundsException(index + " >= " +elementCount);}elementData[index] = obj;}//刪除某個下標的元素public synchronized void removeElementAt(int index) {modCount++;if (index >= elementCount) {throw new ArrayIndexOutOfBoundsException(index + " >= " +elementCount);}else if (index < 0) {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坐標后添加objpublic 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++;}//矢量隊列末尾添加元素public synchronized void addElement(E obj) {modCount++;ensureCapacityHelper(elementCount + 1);elementData[elementCount++] = obj;}//刪除obj元素public synchronized boolean removeElement(Object obj) {modCount++;int i = indexOf(obj);if (i >= 0) {removeElementAt(i);return true;}return false;}//清空所有元素public synchronized void removeAllElements() {modCount++; // Let gc do its workfor (int i = 0; i < elementCount; i++)elementData[i] = null;elementCount = 0;}//克隆public synchronized Object clone() {try {@SuppressWarnings("unchecked")Vector<E> v = (Vector<E>) super.clone();v.elementData = Arrays.copyOf(elementData, elementCount);v.modCount = 0;return v;} catch (CloneNotSupportedException e) { // this shouldn't happen, since we are Cloneablethrow new InternalError(e);}}//生成數組public synchronized Object[] toArray() {return Arrays.copyOf(elementData, elementCount);}@SuppressWarnings("unchecked")public synchronized <T> T[] toArray(T[] a) {if (a.length < elementCount)return (T[]) Arrays.copyOf(elementData, elementCount, a.getClass());System.arraycopy(elementData, 0, a, 0, elementCount);if (a.length > elementCount)a[elementCount] = null;return a;}@SuppressWarnings("unchecked")E elementData(int index) {return (E) elementData[index];}//得到index的元素public synchronized E get(int index) {if (index >= elementCount)throw new ArrayIndexOutOfBoundsException(index);return elementData(index);}//將index元素替換成elementpublic synchronized E set(int index, E element) {if (index >= elementCount)throw new ArrayIndexOutOfBoundsException(index);E oldValue = elementData(index);elementData[index] = element;return oldValue;}//矢量隊列隊尾添加元素public synchronized boolean add(E e) {modCount++;ensureCapacityHelper(elementCount + 1);elementData[elementCount++] = e;return true;}//刪除對象public boolean remove(Object o) {return removeElement(o);}//在index處添加元素public void add(int index, E element) {insertElementAt(element, index);}//刪除index處元素public synchronized E remove(int index) {modCount++;if (index >= elementCount)throw new ArrayIndexOutOfBoundsException(index);E 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 workreturn oldValue;}//清空元素public void clear() {removeAllElements();}//判斷Vector中是否含有所有的Collectionpublic synchronized boolean containsAll(Collection<?> c) {return super.containsAll(c);}//將Collection添加到矢量隊列的隊尾public synchronized boolean addAll(Collection<? extends E> c) {modCount++;Object[] a = c.toArray();int numNew = a.length;ensureCapacityHelper(elementCount + numNew);System.arraycopy(a, 0, elementData, elementCount, numNew);elementCount += numNew;return numNew != 0;}//刪除包含Collection的元素public synchronized boolean removeAll(Collection<?> c) {return super.removeAll(c);}//刪除不存在Collection的元素public synchronized boolean retainAll(Collection<?> c) {return super.retainAll(c);}//在某個index之后追加集合public synchronized boolean addAll(int index, Collection<? extends E> c) {modCount++;if (index < 0 || 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;}//判斷矢量隊列是否相同public synchronized boolean equals(Object o) {return super.equals(o);}//返回hashCodepublic synchronized int hashCode() {return super.hashCode();}//public synchronized String toString() {return super.toString();}//切斷public synchronized List<E> subList(int fromIndex, int toIndex) {return Collections.synchronizedList(super.subList(fromIndex, toIndex),this);}//刪除范圍protected synchronized void removeRange(int fromIndex, int toIndex) {modCount++;int numMoved = elementCount - toIndex;System.arraycopy(elementData, toIndex, elementData, fromIndex,numMoved);// Let gc do its workint newElementCount = elementCount - (toIndex-fromIndex);while (elementCount != newElementCount)elementData[--elementCount] = null;}//序列化private void writeObject(java.io.ObjectOutputStream s)throws java.io.IOException {final java.io.ObjectOutputStream.PutField fields = s.putFields();final Object[] data;synchronized (this) {fields.put("capacityIncrement", capacityIncrement);fields.put("elementCount", elementCount);data = elementData.clone();}fields.put("elementData", data);s.writeFields();}//迭代public synchronized ListIterator<E> listIterator(int index) {if (index < 0 || index > elementCount)throw new IndexOutOfBoundsException("Index: "+index);return new ListItr(index);}public synchronized ListIterator<E> listIterator() {return new ListItr(0);}public synchronized Iterator<E> iterator() {return new Itr();}private class Itr implements Iterator<E> {int cursor; // index of next element to returnint lastRet = -1; // index of last element returned; -1 if no suchint expectedModCount = modCount;public boolean hasNext() { // Racy but within spec, since modifications are checked// within or after synchronization in next/previousreturn cursor != elementCount;}public E next() {synchronized (Vector.this) {checkForComodification();int i = cursor;if (i >= elementCount)throw new NoSuchElementException();cursor = i + 1;return elementData(lastRet = i);}}public void remove() {if (lastRet == -1)throw new IllegalStateException();synchronized (Vector.this) {checkForComodification();Vector.this.remove(lastRet);expectedModCount = modCount;}cursor = lastRet;lastRet = -1;}@Overridepublic void forEachRemaining(Consumer<? super E> action) {Objects.requireNonNull(action);synchronized (Vector.this) {final int size = elementCount;int i = cursor;if (i >= size) {return;}@SuppressWarnings("unchecked")final E[] elementData = (E[]) Vector.this.elementData;if (i >= elementData.length) {throw new ConcurrentModificationException();}while (i != size && modCount == expectedModCount) {action.accept(elementData[i++]);} // update once at end of iteration to reduce heap write trafficcursor = i;lastRet = i - 1;checkForComodification();}}final void checkForComodification() {if (modCount != expectedModCount)throw new ConcurrentModificationException();}}final class ListItr extends Itr implements ListIterator<E> {ListItr(int index) {super();cursor = index;}public boolean hasPrevious() {return cursor != 0;}public int nextIndex() {return cursor;}public int previousIndex() {return cursor - 1;}public E previous() {synchronized (Vector.this) {checkForComodification();int i = cursor - 1;if (i < 0)throw new NoSuchElementException();cursor = i;return elementData(lastRet = i);}}public void set(E e) {if (lastRet == -1)throw new IllegalStateException();synchronized (Vector.this) {checkForComodification();Vector.this.set(lastRet, e);}}public void add(E e) {int i = cursor;synchronized (Vector.this) {checkForComodification();Vector.this.add(i, e);expectedModCount = modCount;}cursor = i + 1;lastRet = -1;}}@Overridepublic synchronized void forEach(Consumer<? super E> action) {Objects.requireNonNull(action);final int expectedModCount = modCount;@SuppressWarnings("unchecked")final E[] elementData = (E[]) this.elementData;final int elementCount = this.elementCount;for (int i=0; modCount == expectedModCount && i < elementCount; i++) {action.accept(elementData[i]);}if (modCount != expectedModCount) {throw new ConcurrentModificationException();}}@Override@SuppressWarnings("unchecked")public synchronized boolean removeIf(Predicate<? super E> filter) {Objects.requireNonNull(filter); // figure out which elements are to be removed// any exception thrown from the filter predicate at this stage// will leave the collection unmodifiedint removeCount = 0;final int size = elementCount;final BitSet removeSet = new BitSet(size);final int expectedModCount = modCount;for (int i=0; modCount == expectedModCount && i < size; i++) {@SuppressWarnings("unchecked")final E element = (E) elementData[i];if (filter.test(element)) {removeSet.set(i);removeCount++;}}if (modCount != expectedModCount) {throw new ConcurrentModificationException();}// shift surviving elements left over the spaces left by removed elementsfinal boolean anyToRemove = removeCount > 0;if (anyToRemove) {final int newSize = size - removeCount;for (int i=0, j=0; (i < size) && (j < newSize); i++, j++) {i = removeSet.nextClearBit(i);elementData[j] = elementData[i];}for (int k=newSize; k < size; k++) {elementData[k] = null; // Let gc do its work}elementCount = newSize;if (modCount != expectedModCount) {throw new ConcurrentModificationException();}modCount++;}return anyToRemove;}@Override@SuppressWarnings("unchecked")public synchronized void replaceAll(UnaryOperator<E> operator) {Objects.requireNonNull(operator);final int expectedModCount = modCount;final int size = elementCount;for (int i=0; modCount == expectedModCount && i < size; i++) {elementData[i] = operator.apply((E) elementData[i]);}if (modCount != expectedModCount) {throw new ConcurrentModificationException();}modCount++;}@SuppressWarnings("unchecked")@Overridepublic synchronized void sort(Comparator<? super E> c) {final int expectedModCount = modCount;Arrays.sort((E[]) elementData, 0, elementCount, c);if (modCount != expectedModCount) {throw new ConcurrentModificationException();}modCount++;}@Overridepublic Spliterator<E> spliterator() {return new VectorSpliterator<>(this, null, 0, -1, 0);}/** Similar to ArrayList Spliterator */static final class VectorSpliterator<E> implements Spliterator<E> {private final Vector<E> list;private Object[] array;private int index; // current index, modified on advance/splitprivate int fence; // -1 until used; then one past last indexprivate int expectedModCount; // initialized when fence set/** Create new spliterator covering the given range */VectorSpliterator(Vector<E> list, Object[] array, int origin, int fence,int expectedModCount) {this.list = list;this.array = array;this.index = origin;this.fence = fence;this.expectedModCount = expectedModCount;}private int getFence() { // initialize on first useint hi;if ((hi = fence) < 0) {synchronized(list) {array = list.elementData;expectedModCount = list.modCount;hi = fence = list.elementCount;}}return hi;}public Spliterator<E> trySplit() {int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;return (lo >= mid) ? null :new VectorSpliterator<E>(list, array, lo, index = mid,expectedModCount);}@SuppressWarnings("unchecked")public boolean tryAdvance(Consumer<? super E> action) {int i;if (action == null)throw new NullPointerException();if (getFence() > (i = index)) {index = i + 1;action.accept((E)array[i]);if (list.modCount != expectedModCount)throw new ConcurrentModificationException();return true;}return false;}@SuppressWarnings("unchecked")public void forEachRemaining(Consumer<? super E> action) {int i, hi; // hoist accesses and checks from loopVector<E> lst; Object[] a;if (action == null)throw new NullPointerException();if ((lst = list) != null) {if ((hi = fence) < 0) {synchronized(lst) {expectedModCount = lst.modCount;a = array = lst.elementData;hi = fence = lst.elementCount;}}elsea = array;if (a != null && (i = index) >= 0 && (index = hi) <= a.length) {while (i < hi)action.accept((E) a[i++]);if (lst.modCount == expectedModCount)return;}}throw new ConcurrentModificationException();}public long estimateSize() {return (long) (getFence() - index);}public int characteristics() {return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;}} }

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原文轉自：

https://blog.csdn.net/chenssy/article/details/37520981

https://blog.csdn.net/qq924862077/article/details/48039567?utm_source=blogxgwz3

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