今天开始，看一下JDK容器源码，这要比比其他jdk源码要简单的多，大部分都能看的懂，这里就不在多言。重点是：
Vector的扩容机制：
若自动增长量小于0，则新长度为当前长度的两倍，否则为旧容量+capacityIncrement
和线程安全的原因就是因为使用了同步控制 synchronized。
public class Vector<E>
extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
//底层实现
protected Object[] elementData;
protected int elementCount;
//容量增长量
protected int capacityIncrement;
public Vector(int initialCapacity, int capacityIncrement) {
super();
if (initialCapacity < 0)
throw new IllegalArgumentException("Illegal Capacity: "+
initialCapacity);
this.elementData = new Object[initialCapacity];
this.capacityIncrement = capacityIncrement;
}
public Vector(int initialCapacity) {
this(initialCapacity, 0);
}
public Vector() {
this(10);
}
<span style="font-family: Arial, Helvetica, sans-serif;">//c.toArray()可能返回一个非Object类型的数组，所以使用Arrays.copyOf创建一个Object[].class类型数组</span><pre name="code" class="java">//扩容机制：若自动增长量小于0则新长度为当前长度的两倍，否则旧容量+capacityIncrement <pre name="code" class="java">//然后在调用 System.arraycopy，并且返回Object数组，
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);
}
public synchronized void copyInto(Object[] anArray) {
System.arraycopy(elementData, 0, anArray, 0, elementCount);
}
//去掉没用（无值）的尾部
public synchronized void trimToSize() {</span><span style="font-size:18px;"> //父类AbstractList中的成员域，fail-fast机制支持
modCount++;
int oldCapacity = elementData.length;
if (elementCount < oldCapacity) {
elementData = Arrays.copyOf(elementData, elementCount);
}
}
//扩容
public synchronized void ensureCapacity(int minCapacity) {
modCount++;
ensureCapacityHelper(minCapacity);
}
//参数为数组的新长度
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);
}
}
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;
}
public synchronized int capacity() {
return elementData.length;
}
public synchronized int size() {
return elementCount;
}
public synchronized boolean isEmpty() {
return elementCount == 0;
}
//返回一个迭代的</span><span style="font-size: 18px; font-family: Arial, Helvetica, sans-serif;">Enumeration</span><span style="font-size:18px;">
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 (E)elementData[count++];
}
}
throw new NoSuchElementException("Vector Enumeration");
}
};
}
public boolean contains(Object o) {
return indexOf(o, 0) >= 0;
}
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;
}
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;
}
public synchronized E elementAt(int index) {
if (index >= elementCount) {
throw new ArrayIndexOutOfBoundsException(index + " >= " + elementCount);
}
return (E)elementData[index];
}
public synchronized E firstElement() {
if (elementCount == 0) {
throw new NoSuchElementException();
}
return (E)elementData[0];
}
public synchronized E lastElement() {
if (elementCount == 0) {
throw new NoSuchElementException();
}
return (E)elementData[elementCount - 1];
}
public synchronized void setElementAt(E obj, int index) {
if (index >= elementCount) {
throw new ArrayIndexOutOfBoundsException(index + " >= " +
elementCount);
}
elementData[index] = obj;
}
//每次改变数组结构时modCount都会+1
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;
}
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++;
}
public synchronized void addElement(E obj) {
modCount++;
ensureCapacityHelper(elementCount + 1);
elementData[elementCount++] = obj;
}
public synchronized boolean removeElement(Object obj) {
modCount++;
int i = indexOf(obj);
if (i >= 0) {
removeElementAt(i);
return true;
}
return false;
}
public synchronized void removeAllElements() {
modCount++;
for (int i = 0; i < elementCount; i++)
elementData[i] = null;
elementCount = 0;
}
//注意java的克隆都是浅复制，若复制一个对象，java clone新开辟一个对象的空间，但是类中引用还是指向原来的地址，</span><span style="font-size:18px;">//并未重新开辟空间
public synchronized Object clone() {
try {
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();
}
}
public synchronized Object[] toArray() {
return Arrays.copyOf(elementData, elementCount);
}
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
public synchronized E get(int index) {
if (index >= elementCount)
throw new ArrayIndexOutOfBoundsException(index);
return (E)elementData[index];
}
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;
}
public synchronized boolean add(E e) {
modCount++;
ensureCapacityHelper(elementCount + 1);
elementData[elementCount++] = e;
return true;
}
public boolean remove(Object o) {
return removeElement(o);
}
public void add(int index, E element) {
insertElementAt(element, index);
}
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;
}
public void clear() {
removeAllElements();
}
//是否包含所有的元素，一个元素一个元素的检查
public synchronized boolean containsAll(Collection<?> c) {
return super.containsAll(c);
}
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;
}
public synchronized boolean removeAll(Collection<?> c) {
return super.removeAll(c);
}
//仅保留此 collection 中那些也包含在指定 collection 的元素
public synchronized boolean retainAll(Collection<?> c) {
return super.retainAll(c);
}
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;
}
public synchronized boolean equals(Object o) {
return super.equals(o);
}
//hashCoded的计算方式 hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());</span><span style="font-size:18px;"> public synchronized int hashCode() {
return super.hashCode();
}
public synchronized String toString() {
return super.toString();
}
public synchronized List<E> subList(int fromIndex, int toIndex) {
return Collections.synchronizedList(super.subList(fromIndex, toIndex),
this);
}
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;
}
private synchronized void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException
{
s.defaultWriteObject();
}
}
</span>
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原文：http://blog.csdn.net/jiaomingliang/article/details/47430851