vector 可实现自动增长的对象数组。本文通过实例代码给大家详细介绍java中的vector，感兴趣的朋友一起看看吧
vector实现了abstractlist抽象类和list接口,和arraylist一样是基于array存储的
vector 是线程安全的,在大多数方法上存在synchronized关键字
//vector存放的元素,初始化默认长度为10
protected object[] elementdata;
//元素个数
protected int elementcount;
//每次扩容大小,默认为0
protected int capacityincrement;
//构造函数，无指定初始化大小和无扩容大小
public vector() {
this(10);
}
//构造函数，指定初始化大小和无扩容大小
public vector(int initialcapacity) {
this(initialcapacity, 0);
}
//构造函数，指定初始化大小和扩容大小
public vector(int initialcapacity, int capacityincrement) {
super();
if (initialcapacity < 0)
throw new illegalargumentexception("illegal capacity: "+
initialcapacity);
this.elementdata = new object[initialcapacity];
this.capacityincrement = capacityincrement;
}
//构造函数,collection集合
public vector(collection<? extends e> c) {
elementdata = c.toarray();
elementcount = elementdata.length;
if (elementdata.getclass() != object[].class)
elementdata = arrays.copyof(elementdata, elementcount, object[].class);
}
//确保扩容的最小容量
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);
}
//扩容
private void grow(int mincapacity) {
int oldcapacity = elementdata.length;
//当扩容大小为0的时候,扩容为原来的2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;
}
ensurecapacity(int mincapacity)方法确保vector的最小长度,当扩容2倍小于mincapacity时,扩容到mincapacity大小,mincapacity不能小于0
最大长度为2的31次方-1
设置大小
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;
}
超过大小的被设置为null
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 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;
}
是否为空
public synchronized boolean isempty() {
return elementcount == 0;
}
设置索引上的元素
public synchronized void setelementat(e obj, int index) {
if (index >= elementcount) {
throw new arrayindexoutofboundsexception(index + " >= " +
elementcount);
}
elementdata[index] = obj;
}
添加元素
public synchronized void addelement(e obj) {
modcount++;
ensurecapacityhelper(elementcount + 1);
elementdata[elementcount++] = obj;
}
扩容
插入元素
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++;
}
扩容
数组拷贝向索引后移动
删除为向前移动
删除元素
public synchronized boolean removeelement(object obj) {
modcount++;
int i = indexof(obj);
if (i >= 0) {
removeelementat(i);
return true;
}
return false;
}
只能删除第一个
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详解
以上就是java中关于vector的详细介绍的详细内容。