Java源代码分析之Vector数组

Vector源码分析

  • 每一个Java程序员应当的特性

    • 可变长数组(grow or shrink
    • 能够使用索引获得值(accessed using an integer index
    • 多线程环境下线程安全
  • 类图

package java.util;

import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.function.UnaryOperator;

/*
vector 通过capacity(容量)和capacityIncrement(增量)两个属性来最化管理存储, capacity 1般都比 size 大。
当知道需要插入大量元素时,可以提早分配给vector较大空间,减少分配内存次数, 从而减少没必要要的开消。
此类的iterator和listIterator方法返回的迭代器是快速失败的:如果该向量在任什么时候间从结构上修改创建迭代器后,
以任何方式,除通过迭代器本身的remove或add方法,迭代器都将抛出ConcurrentModificationException。
因此,在并发的修改,迭代器很快就会完全失败,而不是在将来不肯定的时间任意冒险,不肯定性的行动。
通过elements方法返回的Enumeration不是快速失败的。
注意,迭代器的快速失败行动不能得到保证,由于它是,1般来讲,
不可能作出任何硬性保证不同步并发修改的存在。快速失败迭代器抛出ConcurrentModificationException尽最大努力的基础上。
因此,这将是毛病的编写1个程序,依赖于此异常为它的正确性:
迭代器的快速失败行动应当仅用于检测bug。
从Java 2平台v1.2,这个类是改进来实现List接口,使它成为Java Collections Framework的成员。
不同的是新的集合实现不同,Vector是同步的。
如果不需要线程安全履行,建议代替矢量的使用的ArrayList。
*/

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

// 寄存数据的数组
protected Object[] elementData;

// 实际元素个数
protected int elementCount;

// 容量增量,每次扩容增加的大小,如果 capacityIncrement小雨或等于0,那末容量会每次翻倍double的增长
protected int capacityIncrement;

private static final long serialVersionUID = -2767605614048989439L;
// 数组的初始化,增量的初始化,容量小于0会报异常
public Vector(int initialCapacity, int capacityIncrement) {
super();
if (initialCapacity < 0)
throw new IllegalArgumentException("Illegal Capacity: "+
initialCapacity);
this.elementData = new Object[initialCapacity];
this.capacityIncrement = capacityIncrement;
}

// 指定容量,并且增量为0,每次扩容方法为翻倍
public Vector(int initialCapacity) {
this(initialCapacity, 0);
}

//默许构造方法,默许容量大小为10
public Vector() {
this(10);
}

// 根据指定集合创建vector
// 另外vector的顺序由集合Collection的iterator遍历的顺序来保证
public Vector(Collection<? extends E> c) {
elementData = c.toArray(); // 根据集合生成数组,数组是reallocate的,不存在refer关系
elementCount = elementData.length;
//下面1句话简单理解就是 toArray()返回的其实不1定是Object[]数组(实际类型)
// 具体请看 我的博客文章 http://blog.csdn.net/huzhigenlaohu/article/details/51702737
// c.toArray might (incorrectly) not return Object[] (see 6260652)
if (elementData.getClass() != Object[].class)
elementData = Arrays.copyOf(elementData, elementCount, Object[].class);
}

/**
* anArray 为空会报空指针异常 , anArray的长度不能容纳elementData所有元素汇会报索引越界异常
* 另外 c.toArray not return Object[]时候 报 ArrayStoreException
* 请看 http://blog.csdn.net/huzhigenlaohu/article/details/51702737
*/

public synchronized void copyInto(Object[] anArray) {
System.arraycopy(elementData, 0, anArray, 0, elementCount);
}

// 去掉Vector 数组后面未存入数据的部份,使得Capacity(length) = elementCount
public synchronized void trimToSize() {
//这个 字段含义为 vector 结构(1般指的是大小)被修改的次数
modCount++;
int oldCapacity = elementData.length;
if (elementCount < oldCapacity) {
elementData = Arrays.copyOf(elementData, elementCount);
}
}
//扩容函数(对外暴露的函数,实现看grow)
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 static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
//这个才是看的重点,上面两个函数可以疏忽掉。。。额,说错了,不是疏忽掉而是可以不看
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
// 如果增量大于0那末是的容量+Increment,如果小于等于0,那末容量翻倍
int newCapacity = oldCapacity + ((capacityIncrement > 0) ?
capacityIncrement : oldCapacity);
// 如果根据扩容方法后容量还是小于minCapacity,那末设置扩容后大小为minCapacity
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
//溢出,大于最大允许的容量
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
//根据容量重新reallocate内存,得到1个新数组
elementData = Arrays.copyOf(elementData, newCapacity);
}
// 容量超过最大值处理方式
private static int hugeCapacity(int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
return (minCapacity > MAX_ARRAY_SIZE) ?
Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
}

// 设置vector 的size大小,注意其实不是length,当设置的newsize大于当前的size那末斟酌是不是要扩容,如果小于,那末把过剩的部份全部设置为null
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;
}

//容量
public synchronized int capacity() {
return elementData.length;
}

//元素个数
public synchronized int size() {
return elementCount;
}

//实际存储的元素是不是为空
public synchronized boolean isEmpty() {
return elementCount == 0;
}

//根据索引生成 对应元素的枚举 ,索引为0 为枚举第1个元素,索引为1为枚举第2个元素,and so on
public Enumeration<E> elements() {
return new Enumeration<E>() {
int count = 0;

public boolean hasMoreElements() {
return count < elementCount;
}
//可以看到此方法会抛出异常,在调用的时候务必先调用hasMoreElements进行判断
public E nextElement() {
//提供vector对象锁,保持同步
synchronized (Vector.this) {
if (count < elementCount) {
return elementData(count++);
}
}
throw new NoSuchElementException("Vector Enumeration");
}
};
}

//辨别是不是存在对象 o
public boolean contains(Object o) {
return indexOf(o, 0) >= 0;
}

//返回第1个出现o的位置索引
public int indexOf(Object o) {
return indexOf(o, 0);
}

//主要是判断o是不是为空,其他都是顺序查找,很简单O(n)
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;
}
//从数组后端开始查找起,出现的第1个元素
public synchronized int lastIndexOf(Object o) {
return lastIndexOf(o, elementCount-1);
}
//主要是判断o是不是为空,其他都是顺序查找,很简单O(n)
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;
}

//方法同等于List接口的get(i)方法说
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;
}

//删除从数组左侧起第1个与obj相等的元素
public synchronized boolean removeElement(Object obj) {
modCount++;
int i = indexOf(obj);
if (i >= 0) {
removeElementAt(i);
return true;
}
return false;
}

//删除所有元素
public synchronized void removeAllElements() {
modCount++;
// Let gc do its work
for (int i = 0; i < elementCount; i++)
elementData[i] = null; //gc垃圾回收

elementCount = 0;
}

// clone克隆Vector,重新生成的数组与原来的数组属于不同援用,重新分配内存
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) {//泛型指定生成的数组的类型
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;
}
//没同步,也没判断会不会抛出异常,为何会存在呢?由于这个方法外部不能调用,它由其他内部(public)同步方法调用,保证线程安全
@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);
}

//返回的是旧值
public synchronized E set(int index, E element) {
if (index >= elementCount)
throw new ArrayIndexOutOfBoundsException(index);

E oldValue = elementData(index);
elementData[index] = element;
return oldValue;
}

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);
}

//返回被移除的对象
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;
}

//清空
public void clear() {
removeAllElements();
}

// 批量操作,判断vector中是不是包括集合
// 特别注意:判断集合集合中每一个元素是不是都存在vector中,并没有顺序可言,单独判断,复杂度为O(m*n)
public synchronized boolean containsAll(Collection<?> c) {
return super.containsAll(c);
// 父类方法AbstractCollection
/*
public boolean containsAll(Collection<?> c) {
for (Object e : c)
if (!contains(e))
return false;
return true;
}
*/

}

//集合到vector中,会抛出空指针异常
//特别注意:当正在进行此操作的时候,集合C又被另外1个线程修改,那末得到的vector是不肯定的
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;
}

// 删除指定集合中切存在于vector中的元素
// 遍历vector中每一个元素,判断是不是存在于collection中,存在则删除,复杂度为O(M*n)
public synchronized boolean removeAll(Collection<?> c) {
return super.removeAll(c);
}

// 与前面1个函数功能相反,保存存在于Collection中的vector的元素
public synchronized boolean retainAll(Collection<?> c) {
return super.retainAll(c);
}

//指定索引,插入集合
public synchronized boolean addAll(int index, Collection<? extends E> c) {
modCount++;
if (index < 0 || index > elementCount)
throw new ArrayIndexOutOfBoundsException(index);

Object[] a = c.toArray();
int numNew = a.length;
ensureCapacityHelper(elementCount + numNew);

int numMoved = elementCount - index;
if (numMoved > 0)
System.arraycopy(elementData, index, elementData, index + numNew,
numMoved);

System.arraycopy(a, 0, elementData, index, numNew);
elementCount += numNew;
return numNew != 0;
}

// 顺序、值、大小都要相等,使用父类AbstractList方法实现,顺序由listIterator()保证
public synchronized boolean equals(Object o) {
return super.equals(o);
}
public synchronized int hashCode() {
return super.hashCode();
}
public synchronized String toString() {
return super.toString();
}
//AbstractCollection方法
/*
public String toString() {
Iterator<E> it = iterator();
if (! it.hasNext())
return "[]";

StringBuilder sb = new StringBuilder();
sb.append('[');
for (;;) {
E e = it.next();
sb.append(e == this ? "(this Collection)" : e);
if (! it.hasNext())
return sb.append(']').toString();
sb.append(',').append(' ');
}
}
*/
// 根据指定索引,返回子集合
//特别注意: 返回的子集合还是依赖于此vector的,其实不是重新分配内存的
//对子集合的1切操作将会影响vector的变化,比如对子集合的排序(这个利用的非常广)、清空子集合等都会影响vector元素变化,但是与此同时也要斟酌到多线程的不肯定性
//eg:list.subList(from, to).clear();清空
//由于使用了Collections.synchronizedList进行同步处理(对象锁为当前vector对象),因此对vector的操作和对子集合的操作是同步处理的
public synchronized List<E> subList(int fromIndex, int toIndex) {
return Collections.synchronizedList(super.subList(fromIndex, toIndex),
this);
}

//删除指定范围子集合
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;
}

//序列化
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
final java.io.ObjectOutputStream.PutField fields = s.putFields();
final Object[] data;
synchronized (this) {
fields.put("capacityIncrement", capacityIncrement);
fields.put("elementCount", elementCount);
data = elementData.clone();
}
fields.put("elementData", data);
s.writeFields();
}

// 返回指定游标的列表迭代器,此迭代器ListIterator可以向前向后迭代,比普通iterator()方法强大Itr,推荐使用
public synchronized ListIterator<E> listIterator(int index) {
if (index < 0 || index > elementCount)
throw new IndexOutOfBoundsException("Index: "+index);
return new ListItr(index);
}

//同上1个方法,默许游标位置为起始位置0
public synchronized ListIterator<E> listIterator() {
return new ListItr(0);
}

//返回1个迭代器
public synchronized Iterator<E> iterator() {
return new Itr();
}

/**
* An optimized version of AbstractList.Itr
*/

//迭代器默许实现,会出现fail-fast机制
private class Itr implements Iterator<E> {
int cursor; // index of next element to return
int lastRet = -1; // index of last element returned; ⑴ 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();//检查在迭代期间,检查vector是不是存在结构修改
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();
}
}

//列表迭代器,可以向前向后遍历
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;
}
}
//jdk1.8 新加入的方法,遍历vector中每一个元素,并利用于action行动,支持lambda表达式
@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();
}
}
//支持lambda表达式,判断是不是复合某种条件,然后做其他操作
@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);//位集合,记录符合条件的元素的索引
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();
}

//删除符合条件的元素,左移
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;
}
//支持lambda表达式,对全部元素进行替换操作
@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++;
}
// Arrays.sort 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; // ⑴ 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;
}
}
}

Vector使用案例

  • subList() 用法
/**
* Created by Genge on 2016-06⑴9.
*/

public class Solution {
public static void main(String[] args) {
Vector<String> vector = new Vector<String>();
vector.add("Genge");
vector.add("Hello");
vector.add("World");
System.out.println("处理前的结果:");
Iterator<String> iterator = vector.iterator();
while (iterator.hasNext()) {
System.out.println(iterator.next());
}

List<String> sublist = vector.subList(1, 2);

sublist.clear();

sublist.add("SB");
sublist.add("Huangdou");

System.out.println("处理后结果:");
Iterator<String> iter = vector.iterator();
while (iter.hasNext()) {
System.out.println(iter.next());
}
}
}

结果图以下:

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