详解Java中的Vector
发布时间:2020-12-14 21:21:31 所属栏目:Java 来源:网络整理
导读: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10protected Object[] elementData;//元素个数protected int elementCount;//
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; }
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,anArray,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++; }
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 -我是签名---------------------------- 详解 以上所述是小编给大家介绍的Java中的Vector,希望对大家有所帮助,如果大家有任何疑问请给我留言,小编会及时回复大家的。在此也非常感谢大家对编程小技巧网站的支持! (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |