1，它是線程安全的ArrayList(方法都有synchronized)。
2，Arraylist無限擴容，擴容方式爲在曾經的容量size加上某個參數的值（在add中是加1）和capacity進行比較，如果capacity小，那麼capacity=1.5*capacity + 1，如果此時capacity還是小，那麼新容量爲size加上某個參數的值（在add中是加1）
Vector爲有固定的增量，其他一樣，在決定新容量的時候爲，判斷增量參數是否大於零，是則增量加上舊容量，否則就容量*2
package java.util;
public class Vector<E>
extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
/*
*使用Object數組的方式來實現
*/
protected Object[] elementData;
/**
* 集合中元素個數
*/
protected int elementCount;
/**
* 作用在於需要擴容的時候，把這個值加上舊容量就是新的容量了，比ArrayList要簡單
*/
protected int capacityIncrement;
/** use serialVersionUID from JDK 1.0.2 for interoperability */
private static final long serialVersionUID = -2767605614048989439L;
/**
* 同ArrayList一樣使用Object數組保存元素，指定容量和增量
*/
public Vector(int initialCapacity, int capacityIncrement) {
super();
if (initialCapacity < 0)
throw new IllegalArgumentException("Illegal Capacity: "+
initialCapacity);
this.elementData = new Object[initialCapacity];
this.capacityIncrement = capacityIncrement;
}
/**
* 略
*/
public Vector(int initialCapacity) {
this(initialCapacity, 0);
}
/**
* 略
*/
public Vector() {
this(10);
}
/**
* 最後爲判斷elementData是否爲Object[]類型
*/
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);
}
/**
* 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);
}
/**
* 直接把容量設置爲元素個數，也就是把空的位置捨棄
*/
public synchronized void trimToSize() {
modCount++;
int oldCapacity = elementData.length;
if (elementCount < oldCapacity) {
elementData = Arrays.copyOf(elementData, elementCount);
}
}
/**
* 略，他會調用下一個方法
*/
public synchronized void ensureCapacity(int minCapacity) {
modCount++;
ensureCapacityHelper(minCapacity);
}
/**
* Vector爲有固定的增量，其他ArrayList一樣，在決定新容量的時候爲，判斷增量參數是否大於零，是則增量加上舊容量，否則就容量*2
*/
private void ensureCapacityHelper(int minCapacity) {
int oldCapacity = elementData.length;
if (minCapacity > oldCapacity) {
Object[] oldData = elementData;
int newCapacity = (capacityIncrement > 0) ?
(oldCapacity + capacityIncrement) : (oldCapacity * 2);
if (newCapacity < minCapacity) {
newCapacity = minCapacity;
}
elementData = Arrays.copyOf(elementData, newCapacity);
}
}
/**
* 設置新容量，比舊元素個數多就不說了，但是小的話就會捨棄後面多的元素
*/
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;
}
/**
* 略
*/
public synchronized int capacity() {
return elementData.length;
}
/**
* 略
*/
public synchronized int size() {
return elementCount;
}
/**
* 略
*/
public synchronized boolean isEmpty() {
return elementCount == 0;
}
/**
*Enumeration是個接口，不是類，再次，這個東西就是爲了實現遍歷的，現在已經被迭代器Iterator取代了
*/
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");
}
};
}
/**
* 判斷是否包含某個元素
*/
public boolean contains(Object o) {
return indexOf(o, 0) >= 0;
}
/**
* 返回元素在集合中的索引
*/
public int indexOf(Object o) {
return indexOf(o, 0);
}
/**
* 從參數index開始向Object數組開始向後查找，找到好說，沒找到放回-1
*/
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;
}
/**
* 從後向前查找元素(o)。並返回元素的索引
*/
public synchronized int lastIndexOf(Object o) {
return lastIndexOf(o, elementCount-1);
}
/**
* 類似，略
*/
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;
}
/**
* 按照索引返回元素
*/
public synchronized E elementAt(int index) {
if (index >= elementCount) {
throw new ArrayIndexOutOfBoundsException(index + " >= " + elementCount);
}
return elementData(index);
}
/**
* 略
*/
public synchronized E firstElement() {
if (elementCount == 0) {
throw new NoSuchElementException();
}
return elementData(0);
}
/**
* 略
*/
public synchronized E lastElement() {
if (elementCount == 0) {
throw new NoSuchElementException();
}
return elementData(elementCount - 1);
}
/**
* 略，設置
*/
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，index後面的每個元素向前移動一位，最後空的位置留空
*/
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 */
}
/**
* 指定位置插入一個元素，index後面的每個元素向前移動一位
*/
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++;
}
/**
* 在最後一個元素後面增加元素
*/
public synchronized void addElement(E obj) {
modCount++;
ensureCapacityHelper(elementCount + 1);
elementData[elementCount++] = obj;
}
/**
* 先找到參數元素的索引，再按照索引刪除元素
*/
public synchronized boolean removeElement(Object obj) {
modCount++;
int i = indexOf(obj);
if (i >= 0) {
removeElementAt(i);
return true;
}
return false;
}
/**
* 略
*/
public synchronized void removeAllElements() {
modCount++;
// Let gc do its work
for (int i = 0; i < elementCount; i++)
elementData[i] = null;
elementCount = 0;
}
/**
* Returns a clone of this vector. The copy will contain a
* reference to a clone of the internal data array, not a reference
* to the original internal data array of this {@code Vector} object.
*
* @return a clone of this vector
*/
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 Cloneable
throw new InternalError();
}
}
/**
* Returns an array containing all of the elements in this Vector
* in the correct order.
*
* @since 1.2
*/
public synchronized Object[] toArray() {
return Arrays.copyOf(elementData, elementCount);
}
/**
* Returns an array containing all of the elements in this Vector in the
* correct order; the runtime type of the returned array is that of the
* specified array. If the Vector fits in the specified array, it is
* returned therein. Otherwise, a new array is allocated with the runtime
* type of the specified array and the size of this Vector.
*
* <p>If the Vector fits in the specified array with room to spare
* (i.e., the array has more elements than the Vector),
* the element in the array immediately following the end of the
* Vector is set to null. (This is useful in determining the length
* of the Vector <em>only</em> if the caller knows that the Vector
* does not contain any null elements.)
*
* @param a the array into which the elements of the Vector are to
* be stored, if it is big enough; otherwise, a new array of the
* same runtime type is allocated for this purpose.
* @return an array containing the elements of the Vector
* @throws ArrayStoreException if the runtime type of a is not a supertype
* of the runtime type of every element in this Vector
* @throws NullPointerException if the given array is null
* @since 1.2
*/
@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;
}
// Positional Access Operations
@SuppressWarnings("unchecked")
E elementData(int index) {
return (E) elementData[index];
}
/**
* Returns the element at the specified position in this Vector.
*
* @param index index of the element to return
* @return object at the specified index
* @throws ArrayIndexOutOfBoundsException if the index is out of range
* ({@code index < 0 || index >= size()})
* @since 1.2
*/
public synchronized E get(int index) {
if (index >= elementCount)
throw new ArrayIndexOutOfBoundsException(index);
return elementData(index);
}
/**
* Replaces the element at the specified position in this Vector with the
* specified element.
*
* @param index index of the element to replace
* @param element element to be stored at the specified position
* @return the element previously at the specified position
* @throws ArrayIndexOutOfBoundsException if the index is out of range
* ({@code index < 0 || index >= size()})
* @since 1.2
*/
public synchronized E set(int index, E element) {
if (index >= elementCount)
throw new ArrayIndexOutOfBoundsException(index);
E oldValue = elementData(index);
elementData[index] = element;
return oldValue;
}
/**
* Appends the specified element to the end of this Vector.
*
* @param e element to be appended to this Vector
* @return {@code true} (as specified by {@link Collection#add})
* @since 1.2
*/
public synchronized boolean add(E e) {
modCount++;
ensureCapacityHelper(elementCount + 1);
elementData[elementCount++] = e;
return true;
}
/**
* Removes the first occurrence of the specified element in this Vector
* If the Vector does not contain the element, it is unchanged. More
* formally, removes the element with the lowest index i such that
* {@code (o==null ? get(i)==null : o.equals(get(i)))} (if such
* an element exists).
*
* @param o element to be removed from this Vector, if present
* @return true if the Vector contained the specified element
* @since 1.2
*/
public boolean remove(Object o) {
return removeElement(o);
}
/**
* Inserts the specified element at the specified position in this Vector.
* Shifts the element currently at that position (if any) and any
* subsequent elements to the right (adds one to their indices).
*
* @param index index at which the specified element is to be inserted
* @param element element to be inserted
* @throws ArrayIndexOutOfBoundsException if the index is out of range
* ({@code index < 0 || index > size()})
* @since 1.2
*/
public void add(int index, E element) {
insertElementAt(element, index);
}
/**
* Removes the element at the specified position in this Vector.
* Shifts any subsequent elements to the left (subtracts one from their
* indices). Returns the element that was removed from the Vector.
*
* @throws ArrayIndexOutOfBoundsException if the index is out of range
* ({@code index < 0 || index >= size()})
* @param index the index of the element to be removed
* @return element that was removed
* @since 1.2
*/
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 work
return oldValue;
}
/**
* Removes all of the elements from this Vector. The Vector will
* be empty after this call returns (unless it throws an exception).
*
* @since 1.2
*/
public void clear() {
removeAllElements();
}
// Bulk Operations
/**
* Returns true if this Vector contains all of the elements in the
* specified Collection.
*
* @param c a collection whose elements will be tested for containment
* in this Vector
* @return true if this Vector contains all of the elements in the
* specified collection
* @throws NullPointerException if the specified collection is null
*/
public synchronized boolean containsAll(Collection<?> c) {
return super.containsAll(c);
}
/**
* Appends all of the elements in the specified Collection to the end of
* this Vector, in the order that they are returned by the specified
* Collection's Iterator. The behavior of this operation is undefined if
* the specified Collection is modified while the operation is in progress.
* (This implies that the behavior of this call is undefined if the
* specified Collection is this Vector, and this Vector is nonempty.)
*
* @param c elements to be inserted into this Vector
* @return {@code true} if this Vector changed as a result of the call
* @throws NullPointerException if the specified collection is null
* @since 1.2
*/
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;
}
/**
* Removes from this Vector all of its elements that are contained in the
* specified Collection.
*
* @param c a collection of elements to be removed from the Vector
* @return true if this Vector changed as a result of the call
* @throws ClassCastException if the types of one or more elements
* in this vector are incompatible with the specified
* collection (optional)
* @throws NullPointerException if this vector contains one or more null
* elements and the specified collection does not support null
* elements (optional), or if the specified collection is null
* @since 1.2
*/
public synchronized boolean removeAll(Collection<?> c) {
return super.removeAll(c);
}
/**
* Retains only the elements in this Vector that are contained in the
* specified Collection. In other words, removes from this Vector all
* of its elements that are not contained in the specified Collection.
*
* @param c a collection of elements to be retained in this Vector
* (all other elements are removed)
* @return true if this Vector changed as a result of the call
* @throws ClassCastException if the types of one or more elements
* in this vector are incompatible with the specified
* collection (optional)
* @throws NullPointerException if this vector contains one or more null
* elements and the specified collection does not support null
* elements (optional), or if the specified collection is null
* @since 1.2
*/
public synchronized boolean retainAll(Collection<?> c) {
return super.retainAll(c);
}
/**
* Inserts all of the elements in the specified Collection into this
* Vector at the specified position. Shifts the element currently at
* that position (if any) and any subsequent elements to the right
* (increases their indices). The new elements will appear in the Vector
* in the order that they are returned by the specified Collection's
* iterator.
*
* @param index index at which to insert the first element from the
* specified collection
* @param c elements to be inserted into this Vector
* @return {@code true} if this Vector changed as a result of the call
* @throws ArrayIndexOutOfBoundsException if the index is out of range
* ({@code index < 0 || index > size()})
* @throws NullPointerException if the specified collection is null
* @since 1.2
*/
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;
}
/**
* Compares the specified Object with this Vector for equality. Returns
* true if and only if the specified Object is also a List, both Lists
* have the same size, and all corresponding pairs of elements in the two
* Lists are <em>equal</em>. (Two elements {@code e1} and
* {@code e2} are <em>equal</em> if {@code (e1==null ? e2==null :
* e1.equals(e2))}.) In other words, two Lists are defined to be
* equal if they contain the same elements in the same order.
*
* @param o the Object to be compared for equality with this Vector
* @return true if the specified Object is equal to this Vector
*/
public synchronized boolean equals(Object o) {
return super.equals(o);
}
/**
* Returns the hash code value for this Vector.
*/
public synchronized int hashCode() {
return super.hashCode();
}
/**
* Returns a string representation of this Vector, containing
* the String representation of each element.
*/
public synchronized String toString() {
return super.toString();
}
/**
* Returns a view of the portion of this List between fromIndex,
* inclusive, and toIndex, exclusive. (If fromIndex and toIndex are
* equal, the returned List is empty.) The returned List is backed by this
* List, so changes in the returned List are reflected in this List, and
* vice-versa. The returned List supports all of the optional List
* operations supported by this List.
*
* <p>This method eliminates the need for explicit range operations (of
* the sort that commonly exist for arrays). Any operation that expects
* a List can be used as a range operation by operating on a subList view
* instead of a whole List. For example, the following idiom
* removes a range of elements from a List:
* <pre>
* list.subList(from, to).clear();
* </pre>
* Similar idioms may be constructed for indexOf and lastIndexOf,
* and all of the algorithms in the Collections class can be applied to
* a subList.
*
* <p>The semantics of the List returned by this method become undefined if
* the backing list (i.e., this List) is <i>structurally modified</i> in
* any way other than via the returned List. (Structural modifications are
* those that change the size of the List, or otherwise perturb it in such
* a fashion that iterations in progress may yield incorrect results.)
*
* @param fromIndex low endpoint (inclusive) of the subList
* @param toIndex high endpoint (exclusive) of the subList
* @return a view of the specified range within this List
* @throws IndexOutOfBoundsException if an endpoint index value is out of range
* {@code (fromIndex < 0 || toIndex > size)}
* @throws IllegalArgumentException if the endpoint indices are out of order
* {@code (fromIndex > toIndex)}
*/
public synchronized List<E> subList(int fromIndex, int toIndex) {
return Collections.synchronizedList(super.subList(fromIndex, toIndex),
this);
}
/**
* Removes from this list all of the elements whose index is between
* {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
* Shifts any succeeding elements to the left (reduces their index).
* This call shortens the list by {@code (toIndex - fromIndex)} elements.
* (If {@code toIndex==fromIndex}, this operation has no effect.)
*/
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;
}
/**
* Save the state of the {@code Vector} instance to a stream (that
* is, serialize it). This method is present merely for synchronization.
* It just calls the default writeObject method.
*/
private synchronized void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException
{
s.defaultWriteObject();
}
/**
* Returns a list iterator over the elements in this list (in proper
* sequence), starting at the specified position in the list.
* The specified index indicates the first element that would be
* returned by an initial call to {@link ListIterator#next next}.
* An initial call to {@link ListIterator#previous previous} would
* return the element with the specified index minus one.
*
* <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public synchronized ListIterator<E> listIterator(int index) {
if (index < 0 || index > elementCount)
throw new IndexOutOfBoundsException("Index: "+index);
return new ListItr(index);
}
/**
* Returns a list iterator over the elements in this list (in proper
* sequence).
*
* <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
*
* @see #listIterator(int)
*/
public synchronized ListIterator<E> listIterator() {
return new ListItr(0);
}
/**
* Returns an iterator over the elements in this list in proper sequence.
*
* <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
*
* @return an iterator over the elements in this list in proper sequence
*/
public synchronized Iterator<E> iterator() {
return new Itr();
}
/**
* An optimized version of AbstractList.Itr
*/
private class Itr implements Iterator<E> {
int cursor; // index of next element to return
int lastRet = -1; // index of last element returned; -1 if no such
int expectedModCount = modCount;
public boolean hasNext() {
// Racy but within spec, since modifications are checked
// within or after synchronization in next/previous
return 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;
}
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
/**
* An optimized version of AbstractList.ListItr
*/
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;
}
}
}