1. Vector简介
- Vector继承AbstractList实现了List, RandomAccess, Cloneable, java.io.Serializable接口;
- Vector本质上是线程安全的动态可扩容的数组，区别于ArrayList是非线程安全的动态可扩容的数组，两者的API基本相同；
- Vector扩容可以自定义或默认每次扩容后新容量=2*老容量；
- Vector即使是线程安全的，由于迭代器的特性，Vector中fail-fast机制仍然是不可缺少的；
- Vector提高了可以直接得到列表当前容量的API capacity()函数，而ArrayList不可；
2. Vector UML简图
API 概述
Vector类中定义的字段
protected Object[] elementData; //存储元素的数组
protected int elementCount;//记录动态数组的size,实际含的元素个数
protected int capacityIncrement; //自定义的每次扩容大小，在初始化时设定
private static final long serialVersionUID = -2767605614048989439L;
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
- Vector类中引入了capacityIncrement字段，可以有用户定义每次扩容的大小，确定就是一次指定，以后扩容都扩大一样的大小，即为capacityInCrement.
使用public Vector(int initialCapacity, int capacityIncrement)类型的构造函数即可指定.
*MAX_ARRAY_SIZE 是由于某些虚拟机将header words也保存在数据中，为了这类虚拟机，故数据扩容的最大容量为MAX_ARRAY_SIZE.当然，对于没有将header words 保存在数据中的虚拟机，扩容机制可能仍会扩成Integer.MAX_VALUE.
具体的细节见源码hugeCapactiy函数。
直接继承超类的字段
protected transient int modCount = 0; //继承自AbstractList超类
构造函数
public Vector(int initialCapacity, int capacityIncrement) //每次扩容都按照指定的大小
public Vector(int initialCapacity) //初始化容量大小，扩容机制采用2倍扩容
public Vector() //默认容量为10，扩容机制采用2倍扩容
public Vector(Collection<? extends E> c) //一次性加入一个集合，容量指定为加入的元素的个数
Override或新增的public protected方法
-------------将列表转成数组的方法------------------
synchronized void copyInto(Object[] anArray)
synchronized Object[] toArray()
synchronized <T> T[] toArray(T[] a)
--------------修改列表容量的方法-------------------
synchronized void trimToSize()
synchronized void ensureCapacity(int minCapacity) //方法内调用ensureCapacityHelper->grow扩容
--------------得到capacity size 判空的方法----------
synchronized int capacity()
synchronized int size()
synchronized boolean isEmpty()
--------------得到迭代器的方法-----------------------
Enumeration<E> elements()
synchronized ListIterator<E> listIterator(int index)
synchronized ListIterator<E> listIterator()
synchronized Iterator<E> iterator()
--------------查询元素位置和是否存在的方法------------
boolean contains(Object o)
synchronized boolean containsAll(Collection<?> c)
int indexOf(Object o)
synchronized int indexOf(Object o, int index)
synchronized int lastIndexOf(Object o)
synchronized int lastIndexOf(Object o, int index)
------------返回元素的方法---------------------------
synchronized E elementAt(int index)
synchronized E firstElement()
synchronized E lastElement()
E elementData(int index)
synchronized E get(int index)
------------修改元素的方法----------------------------
synchronized void setElementAt(E obj, int index)
synchronized E set(int index, E element)
------------删除元素的方法----------------------------
synchronized void removeElementAt(int index)
synchronized boolean removeElement(Object obj)
synchronized void removeAllElements()
void clear() //等价于removeAllElements()
boolean remove(Object o)
synchronized E remove(int index)
synchronized boolean removeAll(Collection<?> c)
synchronized boolean retainAll(Collection<?> c)
-------------增加元素的方法-----------------------------
synchronized void insertElementAt(E obj, int index)
synchronized void addElement(E obj)
void add(int index, E element)
synchronized boolean add(E e)
synchronized boolean addAll(Collection<? extends E> c)
synchronized boolean addAll(int index, Collection<? extends E> c)
-----------------克隆列表的方法-------------------------
synchronized Object clone()
-----------返回子列表的方法-----------------------------
synchronized List<E> subList(int fromIndex, int toIndex)
----------Override超类的方法,非同步方法变同步------------
synchronized boolean equals(Object o) //继承自AbstractList
synchronized int hashCode() //继承自AbstractList
synchronized String toString() //继承自AbstractColletion
-----------protected方法--------------------------------
synchronized void removeRange(int fromIndex, int toIndex)
------------java8函数新加的方法--------------------------
synchronized void forEach(Consumer<? super E> action)
synchronized boolean removeIf(Predicate<? super E> filter)
synchronized void replaceAll(UnaryOperator<E> operator)
synchronized void sort(Comparator<? super E> c)
Spliterator<E> spliterator()
----------奇葩的一个方法---------------------------------
synchronized void setSize(int newSize)
来自接口的default方法或直接继承超类的方法
default Stream<E> stream()
default Stream<E> parallelStream()
private方法
----------扩容的方法-----------
void ensureCapacityHelper(int minCapacity)
void grow(int minCapacity)
static int hugeCapacity(int minCapacity)
void readObject(ObjectInputStream in)
void writeObject(java.io.ObjectOutputStream s)
3. Vector 源码介绍(基于jdk1.8.0_231）
package java.util;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.StreamCorruptedException;
import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.function.UnaryOperator;
public class Vector<E>
extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
/**
* The array buffer into which the components of the vector are
* stored. The capacity of the vector is the length of this array buffer,
* and is at least large enough to contain all the vector's elements.
*
* <p>Any array elements following the last element in the Vector are null.
*
* @serial
*/
//存放数据的地方
protected Object[] elementData;
/**
* The number of valid components in this {@code Vector} object.
* Components {@code elementData[0]} through
* {@code elementData[elementCount-1]} are the actual items.
*
* @serial
*/
//记录存放Vector中实际含有的元素个数，
protected int elementCount;
/**
* The amount by which the capacity of the vector is automatically
* incremented when its size becomes greater than its capacity. If
* the capacity increment is less than or equal to zero, the capacity
* of the vector is doubled each time it needs to grow.
*
* @serial
*/
//
protected int capacityIncrement;
/** use serialVersionUID from JDK 1.0.2 for interoperability */
private static final long serialVersionUID = -2767605614048989439L;
/**
* Constructs an empty vector with the specified initial capacity and
* capacity increment.
*
* @param initialCapacity the initial capacity of the vector
* @param capacityIncrement the amount by which the capacity is
* increased when the vector overflows
* @throws IllegalArgumentException if the specified initial capacity
* is negative
*/
public Vector(int initialCapacity, int capacityIncrement) {
super();
if (initialCapacity < 0)
throw new IllegalArgumentException("Illegal Capacity: "+
initialCapacity);
this.elementData = new Object[initialCapacity];
this.capacityIncrement = capacityIncrement;
}
/**
* Constructs an empty vector with the specified initial capacity and
* with its capacity increment equal to zero.
*
* @param initialCapacity the initial capacity of the vector
* @throws IllegalArgumentException if the specified initial capacity
* is negative
*/
public Vector(int initialCapacity) {
this(initialCapacity, 0);
}
/**
* Constructs an empty vector so that its internal data array
* has size {@code 10} and its standard capacity increment is
* zero.
*/
//无参构造函数，容量初始化为10
public Vector() {
this(10);
}
/**
* Constructs a vector containing the elements of the specified
* collection, in the order they are returned by the collection's
* iterator.
*
* @param c the collection whose elements are to be placed into this
* vector
* @throws NullPointerException if the specified collection is null
* @since 1.2
*/
//直接将一个集合加入Vector中，容量即为集合的长度
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);
}
/**
* Copies the components of this vector into the specified array.
* The item at index {@code k} in this vector is copied into
* component {@code k} of {@code anArray}.
*
* @param anArray the array into which the components get copied
* @throws NullPointerException if the given array is null
* @throws IndexOutOfBoundsException if the specified array is not
* large enough to hold all the components of this vector
* @throws ArrayStoreException if a component of this vector is not of
* a runtime type that can be stored in the specified array
* @see #toArray(Object[])
*/
//将vector列表拷贝给另一个列表
public synchronized void copyInto(Object[] anArray) {
System.arraycopy(elementData, 0, anArray, 0, elementCount);
}
/**
* Trims the capacity of this vector to be the vector's current
* size. If the capacity of this vector is larger than its current
* size, then the capacity is changed to equal the size by replacing
* its internal data array, kept in the field {@code elementData},
* with a smaller one. An application can use this operation to
* minimize the storage of a vector.
*/
//将vector容量收缩实际含的元素个数
public synchronized void trimToSize() {
modCount++;
int oldCapacity = elementData.length;
if (elementCount < oldCapacity) {
elementData = Arrays.copyOf(elementData, elementCount);
}
}
/**
* Increases the capacity of this vector, if necessary, to ensure
* that it can hold at least the number of components specified by
* the minimum capacity argument.
*
* <p>If the current capacity of this vector is less than
* {@code minCapacity}, then its capacity is increased by replacing its
* internal data array, kept in the field {@code elementData}, with a
* larger one. The size of the new data array will be the old size plus
* {@code capacityIncrement}, unless the value of
* {@code capacityIncrement} is less than or equal to zero, in which case
* the new capacity will be twice the old capacity; but if this new size
* is still smaller than {@code minCapacity}, then the new capacity will
* be {@code minCapacity}.
*
* @param minCapacity the desired minimum capacity
*/
//检查当前容量是否满足存储元素的最小需要，不够就需要扩容了
public synchronized void ensureCapacity(int minCapacity) {
if (minCapacity > 0) {
modCount++;
ensureCapacityHelper(minCapacity);
}
}
/**
* This implements the unsynchronized semantics of ensureCapacity.
* Synchronized methods in this class can internally call this
* method for ensuring capacity without incurring the cost of an
* extra synchronization.
*
* @see #ensureCapacity(int)
*/
//容量助手，容量不满足最小容量需求，就利用grow函数扩容
private void ensureCapacityHelper(int minCapacity) {
// overflow-conscious code
if (minCapacity - elementData.length > 0)
grow(minCapacity);
}
/**
* The maximum size of array to allocate.
* Some VMs reserve some header words in an array.
* Attempts to allocate larger arrays may result in
* OutOfMemoryError: Requested array size exceeds VM limit
*/
//针对某些虚拟机，Vector容量的最大值，为Integer.MAX_VALUE-8，某些可扩容成Interger.MAX_VALUE
//所以对于上述情况，类库涉及采用了一种安全策略，如果没扩容前已经大于Integer.MAX_VALUE-8，那直接扩充为Interger.MAX_VALUE
//如果没扩容前小于Integer.MAX_VALUE-8，扩容后超过Integer.MAX_VALUE-8，为了安全起见，最大就扩充成Integer.MAX_VALUE-8
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
//扩容机制：如果Vector示例初始化时，设置好了每次扩容的大小是时，每次扩容都是 新容量 = 原容量 + 设置好的扩容大小，
//如果没有设置好扩容大小，新容量 = 2 * 原容量;
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
int newCapacity = oldCapacity + ((capacityIncrement > 0) ?
capacityIncrement : oldCapacity);
//下面的一些处理tricks和ArrayList的grow函数一样
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
elementData = Arrays.copyOf(elementData, newCapacity);
}
//这个hugeCapacity在字段Integer.MAX_VALUE处以说明，是为了自适应虚拟机
private static int hugeCapacity(int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
return (minCapacity > MAX_ARRAY_SIZE) ?
Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
}
/**
* Sets the size of this vector. If the new size is greater than the
* current size, new {@code null} items are added to the end of
* the vector. If the new size is less than the current size, all
* components at index {@code newSize} and greater are discarded.
*
* @param newSize the new size of this vector
* @throws ArrayIndexOutOfBoundsException if the new size is negative
*/
//这个方法很鸡肋，设置Vector的size(即手动设置elementCount,不是容量哦)
//很傻逼的方法，newSize设置比elementCount大，但实际元素那么多，大概率会重新修改原容量大小，
//如果newSize <= elementCount,会把索引newSize到elementCount之间的元素置为null,抹掉了原元素
//背离了Vector动态扩容的初衷了。乱设计API，ArrayList就不会出现这反原则的傻逼方法
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;
}
/**
* Returns the current capacity of this vector.
*
* @return the current capacity (the length of its internal
* data array, kept in the field {@code elementData}
* of this vector)
*/
//得到Vector的容量，请区分容量和数组长度和size elementCount四个概念
//容量capacity= elementData.length; size = elementCount =实际存放元素的个数
public synchronized int capacity() {
return elementData.length;
}
/**
* Returns the number of components in this vector.
*
* @return the number of components in this vector
*/
//返回Vector的size(即elementCount 实际存放元素的个数)
public synchronized int size() {
return elementCount;
}
/**
* Tests if this vector has no components.
*
* @return {@code true} if and only if this vector has
* no components, that is, its size is zero;
* {@code false} otherwise.
*/
//检查Vector是否为空，为空，返回true
public synchronized boolean isEmpty() {
return elementCount == 0;
}
/**
* Returns an enumeration of the components of this vector. The
* returned {@code Enumeration} object will generate all items in
* this vector. The first item generated is the item at index {@code 0},
* then the item at index {@code 1}, and so on.
*
* @return an enumeration of the components of this vector
* @see Iterator
*/
//相当于Iterator迭代器，由于历史原因，这里称为枚举器,不过只有拿到对象锁时候，才会迭代
public Enumeration<E> elements() {
return new Enumeration<E>() {
int count = 0;
public boolean hasMoreElements() { //相当于hasNext()
return count < elementCount;
}
public E nextElement() { //相当于next()
synchronized (Vector.this) {
if (count < elementCount) {
return elementData(count++);
}
}
throw new NoSuchElementException("Vector Enumeration");
}
};
}
/**
* Returns {@code true} if this vector contains the specified element.
* More formally, returns {@code true} if and only if this vector
* contains at least one element {@code e} such that
* <tt>(o==null ? e==null : o.equals(e))</tt>.
*
* @param o element whose presence in this vector is to be tested
* @return {@code true} if this vector contains the specified element
*/
//检查是否包含对象o
public boolean contains(Object o) {
return indexOf(o, 0) >= 0;
}
/**
* Returns the index of the first occurrence of the specified element
* in this vector, or -1 if this vector does not contain the element.
* More formally, returns the lowest index {@code i} such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
* or -1 if there is no such index.
*
* @param o element to search for
* @return the index of the first occurrence of the specified element in
* this vector, or -1 if this vector does not contain the element
*/
//得到对象o的索引
public int indexOf(Object o) {
return indexOf(o, 0);
}
/**
* Returns the index of the first occurrence of the specified element in
* this vector, searching forwards from {@code index}, or returns -1 if
* the element is not found.
* More formally, returns the lowest index {@code i} such that
* <tt>(i >= index && (o==null ? get(i)==null : o.equals(get(i))))</tt>,
* or -1 if there is no such index.
*
* @param o element to search for
* @param index index to start searching from
* @return the index of the first occurrence of the element in
* this vector at position {@code index} or later in the vector;
* {@code -1} if the element is not found.
* @throws IndexOutOfBoundsException if the specified index is negative
* @see Object#equals(Object)
*/
//从index位置开始遍历，得到对象o的位置，没有返回-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;
}
/**
* Returns the index of the last occurrence of the specified element
* in this vector, or -1 if this vector does not contain the element.
* More formally, returns the highest index {@code i} such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
* or -1 if there is no such index.
*
* @param o element to search for
* @return the index of the last occurrence of the specified element in
* this vector, or -1 if this vector does not contain the element
*/
//indexOf都是以index位置开始从前往后找，lastIndexOf都是以index位置开始从后往前找
public synchronized int lastIndexOf(Object o) {
return lastIndexOf(o, elementCount-1);
}
/**
* Returns the index of the last occurrence of the specified element in
* this vector, searching backwards from {@code index}, or returns -1 if
* the element is not found.
* More formally, returns the highest index {@code i} such that
* <tt>(i <= index && (o==null ? get(i)==null : o.equals(get(i))))</tt>,
* or -1 if there is no such index.
*
* @param o element to search for
* @param index index to start searching backwards from
* @return the index of the last occurrence of the element at position
* less than or equal to {@code index} in this vector;
* -1 if the element is not found.
* @throws IndexOutOfBoundsException if the specified index is greater
* than or equal to the current size of this vector
*/
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--) //傻逼设计，不如从size找到index好，ArrayList已修正
if (o.equals(elementData[i]))
return i;
}
return -1;
}
/**
* Returns the component at the specified index.
*
* <p>This method is identical in functionality to the {@link #get(int)}
* method (which is part of the {@link List} interface).
*
* @param index an index into this vector
* @return the component at the specified index
* @throws ArrayIndexOutOfBoundsException if the index is out of range
* ({@code index < 0 || index >= size()})
*/
//返回index位置的元素
public synchronized E elementAt(int index) {
if (index >= elementCount) {
throw new ArrayIndexOutOfBoundsException(index + " >= " + elementCount);
}
return elementData(index);
}
/**
* Returns the first component (the item at index {@code 0}) of
* this vector.
*
* @return the first component of this vector
* @throws NoSuchElementException if this vector has no components
*/
//返回第一个元素
public synchronized E firstElement() {
if (elementCount == 0) {
throw new NoSuchElementException();
}
return elementData(0);
}
/**
* Returns the last component of the vector.
*
* @return the last component of the vector, i.e., the component at index
* <code>size() - 1</code>.
* @throws NoSuchElementException if this vector is empty
*/
//返回最后一个元素
public synchronized E lastElement() {
if (elementCount == 0) {
throw new NoSuchElementException();
}
return elementData(elementCount - 1);
}
/**
* Sets the component at the specified {@code index} of this
* vector to be the specified object. The previous component at that
* position is discarded.
*
* <p>The index must be a value greater than or equal to {@code 0}
* and less than the current size of the vector.
*
* <p>This method is identical in functionality to the
* {@link #set(int, Object) set(int, E)}
* method (which is part of the {@link List} interface). Note that the
* {@code set} method reverses the order of the parameters, to more closely
* match array usage. Note also that the {@code set} method returns the
* old value that was stored at the specified position.
*
* @param obj what the component is to be set to
* @param index the specified index
* @throws ArrayIndexOutOfBoundsException if the index is out of range
* ({@code index < 0 || index >= size()})
*/
//更新index位置的元素为obj
public synchronized void setElementAt(E obj, int index) {
if (index >= elementCount) {
throw new ArrayIndexOutOfBoundsException(index + " >= " +
elementCount);
}
elementData[index] = obj;
}
/**
* Deletes the component at the specified index. Each component in
* this vector with an index greater or equal to the specified
* {@code index} is shifted downward to have an index one
* smaller than the value it had previously. The size of this vector
* is decreased by {@code 1}.
*
* <p>The index must be a value greater than or equal to {@code 0}
* and less than the current size of the vector.
*
* <p>This method is identical in functionality to the {@link #remove(int)}
* method (which is part of the {@link List} interface). Note that the
* {@code remove} method returns the old value that was stored at the
* specified position.
*
* @param index the index of the object to remove
* @throws ArrayIndexOutOfBoundsException if the index is out of range
* ({@code index < 0 || index >= size()})
*/
//删除index位置的元素
public synchronized void removeElementAt(int index) {
modCount++;
if (index >= elementCount) {
throw new ArrayIndexOutOfBoundsException(index + " >= " +
elementCount);
}
else if (index < 0) {
throw new ArrayIndexOutOfBoundsException(index);
}
int j = elementCount - index - 1;
if (j > 0) {
System.arraycopy(elementData, index + 1, elementData, index, j); //把index后的元素一次往前移动1位
}
elementCount--;
elementData[elementCount] = null; /* to let gc do its work */
}
/**
* Inserts the specified object as a component in this vector at the
* specified {@code index}. Each component in this vector with
* an index greater or equal to the specified {@code index} is
* shifted upward to have an index one greater than the value it had
* previously.
*
* <p>The index must be a value greater than or equal to {@code 0}
* and less than or equal to the current size of the vector. (If the
* index is equal to the current size of the vector, the new element
* is appended to the Vector.)
*
* <p>This method is identical in functionality to the
* {@link #add(int, Object) add(int, E)}
* method (which is part of the {@link List} interface). Note that the
* {@code add} method reverses the order of the parameters, to more closely
* match array usage.
*
* @param obj the component to insert
* @param index where to insert the new component
* @throws ArrayIndexOutOfBoundsException if the index is out of range
* ({@code index < 0 || index > size()})
*/
// 在index位置插入obj
//Vecttor从index位置开始一次后移1位（逻辑上应该是elementCount先往后移动1位，接着之前元素依次往后覆盖）
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++;
}
/**
* Adds the specified component to the end of this vector,
* increasing its size by one. The capacity of this vector is
* increased if its size becomes greater than its capacity.
*
* <p>This method is identical in functionality to the
* {@link #add(Object) add(E)}
* method (which is part of the {@link List} interface).
*
* @param obj the component to be added
*/
//在尾部添加一个新元素obj
public synchronized void addElement(E obj) {
modCount++;
ensureCapacityHelper(elementCount + 1); //先检查是否需要扩容
elementData[elementCount++] = obj;
}
/**
* Removes the first (lowest-indexed) occurrence of the argument
* from this vector. If the object is found in this vector, each
* component in the vector with an index greater or equal to the
* object's index is shifted downward to have an index one smaller
* than the value it had previously.
*
* <p>This method is identical in functionality to the
* {@link #remove(Object)} method (which is part of the
* {@link List} interface).
*
* @param obj the component to be removed
* @return {@code true} if the argument was a component of this
* vector; {@code false} otherwise.
*/
//按位置移除obj
public synchronized boolean removeElement(Object obj) {
modCount++;
int i = indexOf(obj); //先顺序得到obj的索引
if (i >= 0) {
removeElementAt(i); //在按索引移除
return true;
}
return false; //没有obj
}
/**
* Removes all components from this vector and sets its size to zero.
*
* <p>This method is identical in functionality to the {@link #clear}
* method (which is part of the {@link List} interface).
*/
//清空Vector实例，相当于ArrayList的clear()
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
*/
//浅拷贝，如果元素都是基本类型就是深拷贝
public synchronized Object clone() {
try {
@SuppressWarnings("unchecked")
Vector<E> v = (Vector<E>) super.clone(); //Object的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(e);
}
}
/**
* Returns an array containing all of the elements in this Vector
* in the correct order.
*
* @since 1.2
*/
//Vector列表转数组
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
//返回index位置的元素
@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
*/
//get区别于elementData唯一之处就是上界检查
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
*/
//更新index位置的元素为element,返回老元素，区别于setElementAt的是set有返回老元素，而前者没有返回值
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
*/
//在尾部添加一个新元素
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
*/
//删除一个对象o,等价于removeElemet(E obj)
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
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if this vector contains one or more null
* elements and the specified collection does not support null
* elements
* (<a href="Collection.html#optional-restrictions">optional</a>),
* or if the specified collection is null
* @since 1.2
*/
//求原集合与集合c的差集
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
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if this vector contains one or more null
* elements and the specified collection does not support null
* elements
* (<a href="Collection.html#optional-restrictions">optional</a>),
* or if the specified collection is null
* @since 1.2
*/
//求原集合与集合c的交集
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)}
*/
//返回原集合的子集合，对子集合的修改直接反映在原集合上，且由于子集合被Collections.SynchronizedList包装，子集合也是线程安全的
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;
}
/**
* Loads a {@code Vector} instance from a stream
* (that is, deserializes it).
* This method performs checks to ensure the consistency
* of the fields.
*
* @param in the stream
* @throws java.io.IOException if an I/O error occurs
* @throws ClassNotFoundException if the stream contains data
* of a non-existing class
*/
private void readObject(ObjectInputStream in)
throws IOException, ClassNotFoundException {
ObjectInputStream.GetField gfields = in.readFields();
int count = gfields.get("elementCount", 0);
Object[] data = (Object[])gfields.get("elementData", null);
if (count < 0 || data == null || count > data.length) {
throw new StreamCorruptedException("Inconsistent vector internals");
}
elementCount = count;
elementData = data.clone();
}
/**
* Save the state of the {@code Vector} instance to a stream (that
* is, serialize it).
* This method performs synchronization to ensure the consistency
* of the serialized data.
*/
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();
}
/**
* 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}
*/
//返回双端迭代器
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
*/
//返回顺序单向迭代器
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;
}
@Override
public 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 traffic
cursor = i;
lastRet = i - 1;
checkForComodification();
}
}
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;
}
}
@Override
public 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();
}
}
//按条件删除
@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 unmodified
int 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 elements
final 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;
}
//替换符合operator条件的所有元素
@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++;
}
//按c规则排序
@SuppressWarnings("unchecked")
@Override
public 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++;
}
/**
* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
* and <em>fail-fast</em> {@link Spliterator} over the elements in this
* list.
*
* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
* {@link Spliterator#SUBSIZED}, and {@link Spliterator#ORDERED}.
* Overriding implementations should document the reporting of additional
* characteristic values.
*
* @return a {@code Spliterator} over the elements in this list
* @since 1.8
*/
@Override
public 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/split
private int fence; // -1 until used; then one past last index
private 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 use
int 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 loop
Vector<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;
}
}
else
a = 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;
}
}
}
4. API 总结
5. Vector使用示例
作为线程安全的列表
java8新特性
6. 面试session
- 谈谈Vector的扩容机制？
Vector扩容机制分为两种情况：一种扩容机制由我们自定义每次扩多少容量，另一种每次扩容后的新容量为原容量的2倍。参见grow扩容函数：
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
//如果在初始化Vector使用public Vector(int initialCapacity, int capacityIncrement) 这种构造函数，会指定capacityIncrement每次新增的容量
//否则,新容量 = 老容量 * 2
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);
}
-
谈谈Vector和ArrayList的异同?
相同点：都是动态自动扩容的列表，数据结构都是数组。大部分API都是相同的；
不同点：1. Vector是线程安全的，ArrayList是非线程安全的；2. 扩容机制不同：简单地讲，ArrayList每次扩容机制是 扩容后的新容量为原容量的1.5倍，而Vector扩容机制分为两种情况：
一种扩容机制由我们自定义每次扩多少容量，另一种每次扩容后的新容量为原容量的2倍。3。讲一个API层面，Vector可以得到当前列表容量和size,ArrayList只可以得到当前size而不知容量。 -
既然Vector都是线程安全的类了，迭代的时候还是运行fail-fast机制是否多余？
不多余，虽有在得到迭代器的函数加入synchronized,但在迭代过程中，我们还可以使用Vector类的其他函数（不是迭代器类中包含的函数，如remove add）来修改列表结构，尽管这是单线程的，仍然会抛异常。这也是fail-fast机制，这是符合迭代器涉及原则的，“你决定用迭代器处理列表了，那下面所有的操作都让迭代器类的函数来接手吧”。如增加 删除等操作，使用迭代器类外Vector本身自带的修改列表结构的函数，都会报错。这种场景就像各位的女朋友，既然你选择了它，牵着它的手逛马路，望下别的女孩子，它也会“情绪异常”，逃~
来些例子
import java.util.*;
public class VectorTest {
public static void main(String[] args) {
Vector<Integer> vector = new Vector<>();
vector.addAll(Arrays.asList(2,3,9,4,5));
Iterator<Integer> iterator = vector.iterator(); //握住女朋友的手狂街
vector.add(100);//望了一下别的漂亮姐姐,也不介意多一个
while (iterator.hasNext()) {
int grilfriendbomb = iterator.next(); //女朋友立即发现你在看漂亮姐姐，女朋友立即炸了。
System.out.println(grilfriendbomb); //你早死了
}
}
}
- 结果
Exception in thread "main" java.util.ConcurrentModificationException
at java.util.Vector$Itr.checkForComodification(Vector.java:1210)
at java.util.Vector$Itr.next(Vector.java:1163)
at collectionlearn.VectorTest.main(VectorTest.java:10)
虽然编了个段子，希望足够引起大家注意：迭代器“占有欲”很强，"很会吃醋"，既然选择了它，请坚定的使用它。ArrayList在单线程环境中同样也存在这个问题。总之，如果使用迭代器，请务必坚定的使用它！
package collectionlearn;
import java.util.*;
public class VectorTest {
public static void main(String[] args) {
Vector<Integer> vector = new Vector<>();
vector.addAll(Arrays.asList(2,3,9,4,5));
System.out.println(vector);
ListIterator<Integer> itr = vector.listIterator(); //握住女朋友的手狂街
itr.next();
itr.add(1); //女朋友被猝不及防的亲了一口,使用迭代器类函数修改列表
while (itr.hasPrevious()) {
int grilhhh = itr.previous(); //女朋友哈哈哈
System.out.print(grilhhh+" "); //给你笑
}
System.out.println();
while (itr.hasNext()) {
int gg = itr.next();
System.out.print(gg +" ");
}
}
}
- 结果
[2, 3, 9, 4, 5]
1 2
2 1 3 9 4 5
Process finished with exit code 0
- 被迭代器掏空
package collectionlearn;
import java.util.*;
public class VectorTest {
public static void main(String[] args) {
Vector<Integer> vector = new Vector<>();
vector.addAll(Arrays.asList(2,3,9,4,5));
System.out.println("没有女朋友的时候：" + vector);
Iterator<Integer> iterator = vector.iterator(); //握住女朋友的手狂街
while (iterator.hasNext()) {
int stand = iterator.next();
iterator.remove();//女朋友开始掏空你
System.out.print(stand + " ");
}
System.out.println();
System.out.println("啊,这谁顶得住呀：" + vector);//被女朋友掏空
}
}
- 结果
没有女朋友的时候：[2, 3, 9, 4, 5]
2 3 9 4 5
啊,这谁顶得住呀：[]
- 出去大保健
package collectionlearn;
import java.util.*;
public class VectorTest {
public static void main(String[] args) {
Vector<Integer> vector = new Vector<>();
vector.addAll(Arrays.asList(2,3,9,4,5));
System.out.println("没有女朋友的时候：" + vector);
Iterator<Integer> iterator = vector.iterator(); //找到女朋友
vector.remove(0); //出去大保健
while (iterator.hasNext()) {
int grilfriendbomb = iterator.next(); //立即捕捉到蛛丝马迹，女朋友炸了
System.out.print(grilfriendbomb + " "); //你早死了
}
}
}
- 结果
没有女朋友的时候：[2, 3, 9, 4, 5]
Exception in thread "main" java.util.ConcurrentModificationException
at java.util.Vector$Itr.checkForComodification(Vector.java:1210)
at java.util.Vector$Itr.next(Vector.java:1163)
at collectionlearn.VectorTest.main(VectorTest.java:11)
总结：迭代器就是一个”女朋友“，用它需谨慎。以上几个例子，证明了fail-fast不仅在多线程中提醒程序员，使用迭代器时候一定不要使用迭代器类以外的函数修改列表。fail-fast是迭代器尽最大努力监测列表结构是否被改变，通过当前迭代器实例来改变列表结构不会抛异常，否则会抛ConcurrentModificationException。特别低，for(:)语法糖本质就是Iterator迭代器，上述发生的异常在这个语法糖中更加隐蔽。
package collectionlearn;
import java.util.*;
public class VectorTest {
public static void main(String[] args) {
Vector<Integer> vector = new Vector<>();
vector.addAll(Arrays.asList(2,3,9,4,5));
for (int i : vector){
if(i==3) vector.remove((Object)3); //出去大保健，异地的女朋友立马都感应到，啊你死了
}
System.out.println(vector);
}
}
- 结果
Exception in thread "main" java.util.ConcurrentModificationException
at java.util.Vector$Itr.checkForComodification(Vector.java:1210)
at java.util.Vector$Itr.next(Vector.java:1163)
at collectionlearn.VectorTest.main(VectorTest.java:7)