Vector原理讲解
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一. Vector概述
本节基于JDK1.8.0_60
- Vector是动态数组实现的List，跟ArrayList一样，其容量能自动增长
- Vector是JDK1.0引入了，它的很多实现方法都加入了同步语句，因此是线程安全的
- Vector适用于快速访问和修改，不适用随机插入和删除
- Vector初始容量大小为10，扩容由初始容量和capacityIncrement共同决定
- Vector元素允许为null
- Vector现在已经基本不再使用，如果不需要线程安全的实现，推荐使用ArrayList代替Vector
- 源码解析：Vector源码
public class Vector<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable,java.io.Serializable
二. Vector总结
2.1 Vector存储结构
// 存储元素protected Object[] elementData;// 实际元素个数protected int elementCount;// 扩容时增加量，大于0增加capacityIncrement，否则翻倍protected int capacityIncrement;
2.2 Vector初始化
// 默认实现public Vector() { this(10);}public Vector(int initialCapacity) { this(initialCapacity, 0);}/** * @param initialCapacity 初始容量大小 * @param capacityIncrement 扩容增加值，大于0增加capacityIncrement，否则翻倍 */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(Collection<? extends E> c) { elementData = c.toArray(); elementCount = elementData.length; if (elementData.getClass() != Object[].class) elementData = Arrays.copyOf(elementData, elementCount, Object[].class);}2.3 Vector扩容
Vector在每次增加元素时，都要确保足够的容量。当容量不足以容纳当前的元素个数时，就先看构造方法中传入的容量增长量参数CapacityIncrement是否为0
- 如果不为0，就设置新的容量为旧容量加上容量增长量
- 如果为0，就设置新的容量为旧的容量的2倍
- 如果设置后的新容量还不够，则直接新容量设置为传入的参数（也就是所需的容量）
- 而后同样用Arrays.copyof()方法将元素拷贝到新的数组
newCapacity = oldCapacity + ((capacityIncrement > 0) ? capacityIncrement : oldCapacity);public synchronized void ensureCapacity(int minCapacity) { if (minCapacity > 0) { modCount++; ensureCapacityHelper(minCapacity); }}private void ensureCapacityHelper(int minCapacity) { if (minCapacity - elementData.length > 0)// 需要扩容 grow(minCapacity);}private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;private void grow(int minCapacity) { int oldCapacity = elementData.length; // 扩容大小？capacityIncrement : 翻倍 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);}private static int hugeCapacity(int minCapacity) { if (minCapacity < 0) // overflow throw new OutOfMemoryError(); return (minCapacity > MAX_ARRAY_SIZE) ? Integer.MAX_VALUE : MAX_ARRAY_SIZE;}2.3.1 Vector一次扩容大小
int oldCapacity = elementData.length; // 扩容大小？capacityIncrement : 翻倍 int newCapacity = oldCapacity + ((capacityIncrement > 0) ? capacityIncrement : oldCapacity);Vector扩容大小由当前元素个数oldCapacity = elementData.length与属性capacityIncrement共同决定的：
- capacityIncrement <= 0，扩容大小为oldCapacity，即翻倍
- oldCapacity > 0，扩容大小为oldCapacity的大小
2.3.2 Vector容量大小限制
JDK6及之前的版本中扩容没有限制容量大小，JDK8中限制了容量大小最大为Integer.MAX_VALU（2^31 - 1）
三. Iterator与ListIterator
JDK1.8.0_60 Vector中实现了两种迭代器Iterator：
- 子类AbstractList中实现的Iterator - Itr
- Vector中重写了子类AbstractList中的ListIterator - ListItr
Iterator只能实现顺序向后遍历，ListIterator可实现顺序向后遍历和逆向（顺序向前）遍历
Iterator只能实现remove操作，ListIterator可以实现remove操作，add操作，set操作
四. Fail-Fast机制
final void checkForComodification() { if (modCount != expectedModCount) throw new ConcurrentModificationException();}Vector也采用了快速失败的机制，通过记录modCount参数来实现。在面对并发的修改时，迭代器很快就会完全失败，而不是冒着在将来某个不确定时间发生任意不确定行为的风险。
它是Java集合的一种错误检测机制。当多个线程对集合进行结构上的改变的操作时，有可能会产生fail-fast机制。记住是有可能，而不是一定。例如：假设存在两个线程（线程1、线程2），线程1通过Iterator在遍历集合A中的元素，在某个时候线程2修改了集合A的结构（是结构上面的修改，而不是简单的修改集合元素的内容），那么这个时候程序就会抛出 ConcurrentModificationException 异常，从而产生fail-fast机制。
五. Vector与ArrayList比较
Vector与ArrayList的最大区别就是Vector是线程安全的，而ArrayList不是线程安全的。另外区别还有：
- ArrayList不可以设置扩展的容量，默认1.5倍
- Vector可以设置扩展的容量，如果没有设置，默认2倍
- ArrayList的无参构造方法中初始容量为0（初次调用add()会更新为10）
- Vector的无参构造方法中初始容量为10
- Vector线程安全
- ArrayList线程不安全
六. Collections.synchronizedList和Vector比较
Vector是java1.0开始使用的，而集合框架从JDK1.2开始加入。
SynchronizedList和Vector最主要的区别：
- SynchronizedList有很好的扩展和兼容功能。他可以将所有的List的子类转成线程安全的类
- 使用SynchronizedList的时候，进行遍历时要手动进行同步处理
- SynchronizedList可以指定锁定的对象
SynchronizedList和Vector的区别
CopyOnWriteArrayList与Collections.synchronizedList的性能对比
package com.src.collection.list;import java.util.ArrayList;import java.util.Collections;import java.util.Iterator;import java.util.List;import java.util.ListIterator;public class SynchronizedListTest { public static void main(String[] args) { ArrayList<Integer> arrayList = new ArrayList<>(); int len = 9000000; for (int i = 0; i < len; i++) { arrayList.add(i); } System.out.println(len + "个数据: "); List<Integer> list = Collections.synchronizedList(arrayList); long start = System.currentTimeMillis(); for (int size = list.size(), i = 0; i < size; i++) { int sta = list.get(i); } System.out.println("for循环遍历耗时： " + (System.currentTimeMillis()-start) + "毫秒！"); long second = System.currentTimeMillis(); Iterator<Integer> iterator = list.iterator(); while (iterator.hasNext()) { int sec = iterator.next(); } System.out.println("迭代器Iterator遍历耗时： " + (System.currentTimeMillis()-second) + "毫秒！"); long third = System.currentTimeMillis(); for (int i : list) {// 也是Iterator实现的 int thi = i; } System.out.println("foreach循环遍历耗时： " + (System.currentTimeMillis()-third) + "毫秒！"); long fourth = System.currentTimeMillis(); ListIterator<Integer> listIterator = list.listIterator(); while (listIterator.hasNext()) { int fou = listIterator.next(); } System.out.println("迭代器ListIterator循环遍历耗时： " + (System.currentTimeMillis()-fourth) + "毫秒！"); long firth = System.currentTimeMillis(); list.forEach(integer -> { int fir = integer; }); System.out.println("forEach循环遍历耗时： "+ (System.currentTimeMillis()-firth) + "毫秒！"); }}9000个数据: for循环遍历耗时： 1毫秒！迭代器Iterator遍历耗时： 2毫秒！foreach循环遍历耗时： 1毫秒！迭代器ListIterator循环遍历耗时： 3毫秒！forEach循环遍历耗时： 84毫秒！90000个数据: for循环遍历耗时： 6毫秒！迭代器Iterator遍历耗时： 5毫秒！foreach循环遍历耗时： 3毫秒！迭代器ListIterator循环遍历耗时： 3毫秒！forEach循环遍历耗时： 96毫秒！900000个数据: for循环遍历耗时： 32毫秒！迭代器Iterator遍历耗时： 21毫秒！foreach循环遍历耗时： 13毫秒！迭代器ListIterator循环遍历耗时： 17毫秒！forEach循环遍历耗时： 97毫秒！9000000个数据: for循环遍历耗时： 265毫秒！迭代器Iterator遍历耗时： 33毫秒！foreach循环遍历耗时： 35毫秒！迭代器ListIterator循环遍历耗时： 33毫秒！forEach循环遍历耗时： 107毫秒！七. Vector遍历比较
package com.src.collection.list;import java.util.Enumeration;import java.util.Iterator;import java.util.ListIterator;import java.util.Vector;/** * Vector遍历效率对比 * JDK1.8.0_60 * */public class VectorTest { public static void main(String[] args) { Vector<Integer> vector = new Vector<>(); int len = 9000; for (int i = 0; i < len; i++) { vector.add(i); } System.out.println(len + "个数据: Vector方法加了synchronized关键字！"); long start = System.currentTimeMillis(); for (int size = vector.size(), i = 0; i < size; i++) { int sta = vector.get(i); } System.out.println("for循环遍历耗时： " + (System.currentTimeMillis()-start) + "毫秒！"); long second = System.currentTimeMillis(); Iterator<Integer> iterator = vector.iterator(); while (iterator.hasNext()) { int sec = iterator.next(); } System.out.println("迭代器Iterator遍历耗时： " + (System.currentTimeMillis()-second) + "毫秒！"); long third = System.currentTimeMillis(); for (int i : vector) {// 也是Iterator实现的 int thi = i; } System.out.println("foreach循环遍历耗时： " + (System.currentTimeMillis()-third) + "毫秒！"); long fourth = System.currentTimeMillis(); ListIterator<Integer> listIterator = vector.listIterator(); while (listIterator.hasNext()) { int fou = listIterator.next(); } System.out.println("迭代器ListIterator循环遍历耗时： " + (System.currentTimeMillis()-fourth) + "毫秒！"); long firth = System.currentTimeMillis(); vector.forEach(integer -> { int fir = integer; }); System.out.println("forEach循环遍历耗时： "+ (System.currentTimeMillis()-firth) + "毫秒！"); long sixth = System.currentTimeMillis(); Enumeration<Integer> elements = vector.elements(); while (elements.hasMoreElements()) { int six = elements.nextElement(); } System.out.println("Enumeration循环耗时： " + (System.currentTimeMillis()-sixth) + "毫秒"); }}运行结果（每次运行都有些差异）:
9000个数据: Vector方法加了synchronized关键字！for循环遍历耗时： 1毫秒！迭代器Iterator遍历耗时： 3毫秒！foreach循环遍历耗时： 2毫秒！迭代器ListIterator循环遍历耗时： 2毫秒！forEach循环遍历耗时： 75毫秒！Enumeration循环耗时： 2毫秒90000个数据: Vector方法加了synchronized关键字！for循环遍历耗时： 3毫秒！迭代器Iterator遍历耗时： 7毫秒！foreach循环遍历耗时： 4毫秒！迭代器ListIterator循环遍历耗时： 4毫秒！forEach循环遍历耗时： 81毫秒！Enumeration循环耗时： 7毫秒900000个数据: Vector方法加了synchronized关键字！for循环遍历耗时： 35毫秒！迭代器Iterator遍历耗时： 34毫秒！foreach循环遍历耗时： 33毫秒！迭代器ListIterator循环遍历耗时： 32毫秒！forEach循环遍历耗时： 87毫秒！Enumeration循环耗时： 27毫秒9000000个数据: Vector方法加了synchronized关键字！for循环遍历耗时： 250毫秒！迭代器Iterator遍历耗时： 258毫秒！foreach循环遍历耗时： 256毫秒！迭代器ListIterator循环遍历耗时： 262毫秒！forEach循环遍历耗时： 93毫秒！Enumeration循环耗时： 173毫秒八. Vector源码
package java.util;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 { private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8; protected Object[] elementData; protected int elementCount; protected int capacityIncrement; private static final long serialVersionUID = -2767605614048989439L; 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); } 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); } public synchronized void trimToSize() { modCount++; int oldCapacity = elementData.length; if (elementCount < oldCapacity) { elementData = Arrays.copyOf(elementData, elementCount); } } 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 void ensureCapacity(int minCapacity) { if (minCapacity > 0) { modCount++; ensureCapacityHelper(minCapacity); } } private void ensureCapacityHelper(int minCapacity) { // overflow-conscious code if (minCapacity - elementData.length > 0) grow(minCapacity); } private void grow(int minCapacity) { // overflow-conscious code int 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) // overflow throw new OutOfMemoryError(); return (minCapacity > MAX_ARRAY_SIZE) ? Integer.MAX_VALUE : MAX_ARRAY_SIZE; } public synchronized int capacity() { return elementData.length; } public synchronized int size() { return elementCount; } public synchronized boolean isEmpty() { return elementCount == 0; } 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"); } }; } 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 elementData(index); } public synchronized E firstElement() { if (elementCount == 0) { throw new NoSuchElementException(); } return elementData(0); } public synchronized E lastElement() { if (elementCount == 0) { throw new NoSuchElementException(); } return elementData(elementCount - 1); } public synchronized void setElementAt(E obj, int index) { if (index >= elementCount) { throw new ArrayIndexOutOfBoundsException(index + " >= " + elementCount); } elementData[index] = obj; } 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 */ } 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++; // Let gc do its work for (int i = 0; i < elementCount; i++) elementData[i] = null; elementCount = 0; } 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(e); } } 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]; } public synchronized E get(int index) { if (index >= elementCount) throw new ArrayIndexOutOfBoundsException(index); return elementData(index); } public synchronized E set(int index, E element) { if (index >= elementCount) throw new ArrayIndexOutOfBoundsException(index); E oldValue = elementData(index); elementData[index] = element; return 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); 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; } public void clear() { removeAllElements(); } 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); } 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); } 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 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(); } 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 return int lastRet = -1; // index of last element returned; -1 if no such int expectedModCount = modCount; public boolean hasNext() { 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(); } } 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(); } } @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; } @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") @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++; } @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; } }}阅读全文
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