Vector 可實現自動增長的物件陣列。本文透過實例程式碼給大家詳細介紹java中的vector，有興趣的朋友一起看看吧
Vector實作了AbstractList抽象類別和List介面,和ArrayList一樣是基於Array儲存的
Vector 是線程安全的,在大多數方法上存在synchronized關鍵字
//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 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)方法確保Vector的最小長度,當擴容2倍小於minCapacity時,擴容到minCapacity大小,minCapacity不能小於0
最大長度為2的31次方-1
#設定大小
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; }
超過大小的被設定為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; }
是否為空
public synchronized boolean isEmpty() { return elementCount == 0; }
設定索引上的元素
public synchronized void setElementAt(E obj, int index) { if (index >= elementCount) { throw new ArrayIndexOutOfBoundsException(index + " >= " + elementCount); } elementData[index] = obj; }
新增元素
public synchronized void addElement(E obj) { modCount++; ensureCapacityHelper(elementCount + 1); elementData[elementCount++] = obj; }
#擴容
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++; }
#擴容
public synchronized boolean removeElement(Object obj) { modCount++; int i = indexOf(obj); if (i >= 0) { removeElementAt(i); return true; } return false; }
-我是簽名------------------- ---------
詳解
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