文章目錄
- 1. Vector 的基本介紹
- 2. 源碼分析
- 3. Vector 和 ArrayList 的比較
1. Vector 的基本介紹
- Vector類的定義說明
- Vector底層也是一個對象數組,
protected Object[] elementData;
- Vector是線程同步的,即線程安全,Vector類的操作方法帶有
synchronized
public synchronized E get(int index) {
if (index > = elementCount)
throw new ArrayIndexOutOfBoundsException(index);
return elementData(index);
}
- 在開發中,需要線程同步安全時,考慮使用Vector
- 案例:
2. 源碼分析
-
底層new Vector()
public Vector() {
this(10);
}
補充:如果是
Vector vector = new Vector(8);
走的方法:
public Vector(int initialCapacity) {
this(initialCapacity, 0);
}
- vector.add(i)
2.1 下面這個方法就添加資料到 vector 集合
public synchronized boolean add(E e) {
modCount++;
ensureCapacityHelper(elementCount + 1);
elementData[elementCount++] = e;
return true;
}
2.2 确定是否需要擴容 條件 :
minCapacity - elementData.length>0
private void ensureCapacityHelper(int minCapacity) {
// overflow-conscious code
if (minCapacity - elementData.length > 0
grow(minCapacity);
}
//newCapacity = oldCapacity + ((capacityIncrement > 0) ?
//capacityIncrement : oldCapacity); 就是擴容兩倍.
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);
}