1.静态变量和成员变量
/**
* 基础数据结构
*/
protected Object[] elementData;
/**
* 数据个数
*/
protected int elementCount;
/**
* 数据增长个数
*/
protected int capacityIncrement;
/** use serialVersionUID from JDK 1.0.2 for interoperability */
private static final long serialVersionUID = -2767605614048989439L;
2. 构造方法
/**
* 两个参数的构造方法，第一个是默认大小，第二个是每次增长大小
*/
public Vector(int initialCapacity, int capacityIncrement) {
super();
if (initialCapacity < 0)
throw new IllegalArgumentException("Illegal Capacity: "+
initialCapacity);
this.elementData = new Object[initialCapacity];
this.capacityIncrement = capacityIncrement;
}
/**
* 只有初始大小的构造方法，默认增长大小为0（这是每次增长为初始大小，即每次增长一倍）
*/
public Vector(int initialCapacity) {
this(initialCapacity, 0);
}
/**
*默认构造方法，默认初始大小为10 ，增长大小为10
*/
public Vector() {
this(10);
}
/**
* 传入集合的构造方法，默认大小为传入集合的大小，增长大小为传入集合大大小
*/
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);
}
3.增删改查
/**
* 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;
}
/**
* 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;
}
/**
* 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
*/
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)
*/
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
*/
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
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;
}
/**
* 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);
}
和arrayList类似，但是这写方法都有同步关键字synchronized。方法线程安全，但是速度更慢了。
总结
- 线程安全，默认大小为10，每次扩容为传入的扩容大小(当没有传入时或者为0时，直接初始值翻倍)
- 基本上所有的对外的方法都带着synchronized，线程安全但是效率低下
- 基础类型和arrayList一样
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