Vector：线程安全List
1、变量定义，底层依然使用数组保存数据
/**
* 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
*/
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
*/
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;2、对于操作方法，基本使用的是synchronized关键字，保证其操作的安全性。
设置大小，判断是否为空等。与ArrayList方法大致一样，添加了线程安全关键字修饰
/**
* 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
*/
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)
*/
public synchronized int capacity() {
return elementData.length;
}
/**
* Returns the number of components in this vector.
*
* @return the number of components in this vector
*/
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.
*/
public synchronized boolean isEmpty() {
return elementCount == 0;
}3、添加元素addElement
/**
* 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
*/
public synchronized void addElement(E obj) {
modCount++;
ensureCapacityHelper(elementCount + 1);
elementData[elementCount++] = obj;
}4、删除元素：removeElement
/**
* 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.
*/
public synchronized boolean removeElement(Object obj) {
modCount++;
int i = indexOf(obj);
if (i >= 0) {
removeElementAt(i);
return true;
}
return false;
}5、get/set：查询与设置
/**
* 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
*/
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
*/
public synchronized E set(int index, E element) {
if (index >= elementCount)
throw new ArrayIndexOutOfBoundsException(index);
E oldValue = elementData(index);
elementData[index] = element;
return oldValue;
}5、add/remove：添加与删除，remove底层调用removeElement
/**
* 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
*/
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
*/
public boolean remove(Object o) {
return removeElement(o);
}总结：Vector是List的一种线程安全的实现，基本操作与ArrayList类似
