【Java集合源码03】Vector源码分析

电玩女神 2023-01-03 04:24 118阅读 0赞

# 简介 #

Vector 类实现了一个动态数组。和 ArrayList 很相似，但是两者是不同的：

*  Vector 是同步访问的。
 *  Vector 包含了许多传统的方法，这些方法不属于集合框架。

Vector 主要用在事先不知道数组的大小，或者只是需要一个可以改变大小的数组的情况。

Vector是线程安全的，但是是遗留类，不推荐使用。内部使用Object数组实现，通过加全局锁synchronized实现线程安全。默认容量为10.

![20201205145755.png][]

> Vector源码分析基于jdk1.8

# 源码 #

源码很简单，没查可说的

## get方法 ##

1.  检查索引是否合法
2.  直接返回elementData\[index\]

public synchronized E get(int index) {
        
            if (index >= elementCount)
                throw new ArrayIndexOutOfBoundsException(index);
    
            return elementData(index);
        }
        
            @SuppressWarnings("unchecked")
        E elementData(int index) {
        
            return (E) elementData[index];
        }

## add方法 ##

1.  先判断是否需要扩容，如果需要，就扩容，
2.  如果扩容增量大于0，就扩容成原容量+增量，否则扩容成原容量的2倍，然后将原数组中元素复制到新数组中
3.  将元素插入到elementCount，也就是原始存在元素的尾部。

public synchronized boolean add(E e) {
 
 modCount++;
 ensureCapacityHelper(elementCount + 1);
 elementData[elementCount++] = e;
 return true;
 }
 
 private void ensureCapacityHelper(int minCapacity) {
 
 // overflow-conscious code
 if (minCapacity - elementData.length > 0)
 grow(minCapacity);
 }
 
 private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
 
 private void grow(int minCapacity) {
 
 // overflow-conscious code
 int oldCapacity = elementData.length;
 // 如果capacityIncrement > 0就扩容成oldCapacity+capacityIncrement
 // 否则扩容成2*oldCapacity
 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);
 }

## 其他一些注释 ##

public class Vector<E>
 extends AbstractList<E>
 implements List<E>, RandomAccess, Cloneable, java.io.Serializable
 {
 
 /**
 * 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.
 *
 * 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.
 * 元素个数
 * @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.
 * 容量增量，如果capacityIncrement<=0, 数组大小扩容成原来的2倍
 * @serial
 */
 protected int capacityIncrement;
 
 /** use serialVersionUID from JDK 1.0.2 for interoperability */
 private static final long serialVersionUID = -2767605614048989439L;
 
 /**
 * Constructs an empty vector with the specified initial capacity and
 * capacity increment.
 *
 * @param initialCapacity the initial capacity of the vector
 * @param capacityIncrement the amount by which the capacity is
 * increased when the vector overflows
 * @throws IllegalArgumentException if the specified initial capacity
 * is negative
 */
 public Vector(int initialCapacity, int capacityIncrement) {
 
 super();
 if (initialCapacity < 0)
 throw new IllegalArgumentException("Illegal Capacity: "+
 initialCapacity);
 this.elementData = new Object[initialCapacity];
 this.capacityIncrement = capacityIncrement;
 }
 
 /**
 * Constructs an empty vector with the specified initial capacity and
 * with its capacity increment equal to zero.
 *
 * @param initialCapacity the initial capacity of the vector
 * @throws IllegalArgumentException if the specified initial capacity
 * is negative
 */
 public Vector(int initialCapacity) {
 
 this(initialCapacity, 0);
 }
 
 /**
 * Constructs an empty vector so that its internal data array
 * has size {@code 10} and its standard capacity increment is
 * zero.
 * 默认容量为10
 */
 public Vector() {
 
 this(10);
 }
 
 /**
 * Constructs a vector containing the elements of the specified
 * collection, in the order they are returned by the collection's
 * iterator.
 *
 * @param c the collection whose elements are to be placed into this
 * vector
 * @throws NullPointerException if the specified collection is null
 * @since 1.2
 */
 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);
 }
 
 /**
 * Copies the components of this vector into the specified array.
 * The item at index {@code k} in this vector is copied into
 * component {@code k} of {@code anArray}.
 *
 * @param anArray the array into which the components get copied
 * @throws NullPointerException if the given array is null
 * @throws IndexOutOfBoundsException if the specified array is not
 * large enough to hold all the components of this vector
 * @throws ArrayStoreException if a component of this vector is not of
 * a runtime type that can be stored in the specified array
 * @see #toArray(Object[])
 */
 public synchronized void copyInto(Object[] anArray) {
 
 System.arraycopy(elementData, 0, anArray, 0, elementCount);
 }
 
 /**
 * Trims the capacity of this vector to be the vector's current
 * size. If the capacity of this vector is larger than its current
 * size, then the capacity is changed to equal the size by replacing
 * its internal data array, kept in the field {@code elementData},
 * with a smaller one. An application can use this operation to
 * minimize the storage of a vector.
 * 将数组大小变成，数组中元素个数的大小
 */
 public synchronized void trimToSize() {
 
 modCount++;
 int oldCapacity = elementData.length;
 if (elementCount < oldCapacity) {
 
 elementData = Arrays.copyOf(elementData, elementCount);
 }
 }
 
 /**
 * 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.
 *
 * 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}.
 * 这个方法是供用户调用的，可以初始化数组的大小
 * @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.
 * 扩容
 * @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;
 // 如果capacityIncrement > 0就扩容成oldCapacity+capacityIncrement
 // 否则扩容成2*oldCapacity
 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;
 }
 
 /**
 * 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
 * 设置数组大小，newSize比当前size大，就复制过去，newSize比当前size小，就将索引大于
 * newSize置null,这里并不缩小数组，还是原数组
 */
 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)
 * 容量就是数组的大小
 */
 public synchronized int capacity() {
 
 return elementData.length;
 }
 
 /**
 * Returns the number of components in this vector.
 *
 * @return the number of components in this vector
 * size就是数组中实际存的元素个数
 */
 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;
 }
 
 /**
 * Returns an enumeration of the components of this vector. The
 * returned {@code Enumeration} object will generate all items in
 * this vector. The first item generated is the item at index {@code 0},
 * then the item at index {@code 1}, and so on.
 * 返回vector中所有元素
 * @return an enumeration of the components of this vector
 * @see Iterator
 */
 public Enumeration<E> elements() {
 
 return new Enumeration<E>() {
 
 int count = 0;
 
 public boolean hasMoreElements() {
 
 return count < elementCount;
 }
 
 public E nextElement() {
 
 synchronized (Vector.this) {
 
 if (count < elementCount) {
 
 return elementData(count++);
 }
 }
 throw new NoSuchElementException("Vector Enumeration");
 }
 };
 }
 
 /**
 * Returns {@code true} if this vector contains the specified element.
 * More formally, returns {@code true} if and only if this vector
 * contains at least one element {@code e} such that
 * <tt>(o==null ? e==null : o.equals(e))</tt>.
 *
 * @param o element whose presence in this vector is to be tested
 * @return {@code true} if this vector contains the specified element
 */
 public boolean contains(Object o) {
 
 return indexOf(o, 0) >= 0;
 }
 
 /**
 * Returns the index of the first occurrence of the specified element
 * in this vector, or -1 if this vector does not contain the element.
 * More formally, returns the lowest index {@code i} such that
 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
 * or -1 if there is no such index.
 *
 * @param o element to search for
 * @return the index of the first occurrence of the specified element in
 * this vector, or -1 if this vector does not contain the element
 */
 public int indexOf(Object o) {
 
 return indexOf(o, 0);
 }
 
 /**
 * Returns the index of the first occurrence of the specified element in
 * this vector, searching forwards from {@code index}, or returns -1 if
 * the element is not found.
 * More formally, returns the lowest index {@code i} such that
 * <tt>(i >= index && (o==null ? get(i)==null : o.equals(get(i))))</tt>,
 * or -1 if there is no such index.
 *
 * @param o element to search for
 * @param index index to start searching from
 * @return the index of the first occurrence of the element in
 * this vector at position {@code index} or later in the vector;
 * {@code -1} if the element is not found.
 * @throws IndexOutOfBoundsException if the specified index is negative
 * @see Object#equals(Object)
 * 从index开始查找o所在的位置
 */
 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;
 }
 
 /**
 * Returns the index of the last occurrence of the specified element
 * in this vector, or -1 if this vector does not contain the element.
 * More formally, returns the highest index {@code i} such that
 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
 * or -1 if there is no such index.
 *
 * @param o element to search for
 * @return the index of the last occurrence of the specified element in
 * this vector, or -1 if this vector does not contain the element
 * 这些都比较简单，不再注释了
 */
 public synchronized int lastIndexOf(Object o) {
 
 return lastIndexOf(o, elementCount-1);
 }
 
 /**
 * Returns the index of the last occurrence of the specified element in
 * this vector, searching backwards from {@code index}, or returns -1 if
 * the element is not found.
 * More formally, returns the highest index {@code i} such that
 * <tt>(i <= index && (o==null ? get(i)==null : o.equals(get(i))))</tt>,
 * or -1 if there is no such index.
 *
 * @param o element to search for
 * @param index index to start searching backwards from
 * @return the index of the last occurrence of the element at position
 * less than or equal to {@code index} in this vector;
 * -1 if the element is not found.
 * @throws IndexOutOfBoundsException if the specified index is greater
 * than or equal to the current size of this vector
 */
 public synchronized int lastIndexOf(Object o, int index) {
 
 if (index >= elementCount)
 throw new IndexOutOfBoundsException(index + " >= "+ elementCount);
 
 if (o == null) {
 
 for (int i = index; i >= 0; i--)
 if (elementData[i]==null)
 return i;
 } else {
 
 for (int i = index; i >= 0; i--)
 if (o.equals(elementData[i]))
 return i;
 }
 return -1;
 }
 
 /**
 * Returns the component at the specified index.
 *
 * This method is identical in functionality to the {@link #get(int)}
 * method (which is part of the {@link List} interface).
 *
 * @param index an index into this vector
 * @return the component at the specified index
 * @throws ArrayIndexOutOfBoundsException if the index is out of range
 * ({@code index < 0 || index >= size()})
 * 返回elementData[index]
 */
 public synchronized E elementAt(int index) {
 
 if (index >= elementCount) {
 
 throw new ArrayIndexOutOfBoundsException(index + " >= " + elementCount);
 }
 
 return elementData(index);
 }
 
 /**
 * Returns the first component (the item at index {@code 0}) of
 * this vector.
 *
 * @return the first component of this vector
 * @throws NoSuchElementException if this vector has no components
 */
 public synchronized E firstElement() {
 
 if (elementCount == 0) {
 
 throw new NoSuchElementException();
 }
 return elementData(0);
 }
 
 /**
 * Returns the last component of the vector.
 *
 * @return the last component of the vector, i.e., the component at index
 * <code>size() - 1</code>.
 * @throws NoSuchElementException if this vector is empty
 */
 public synchronized E lastElement() {
 
 if (elementCount == 0) {
 
 throw new NoSuchElementException();
 }
 return elementData(elementCount - 1);
 }
 
 /**
 * Sets the component at the specified {@code index} of this
 * vector to be the specified object. The previous component at that
 * position is discarded.
 *
 * The index must be a value greater than or equal to {@code 0}
 * and less than the current size of the vector.
 *
 * This method is identical in functionality to the
 * {@link #set(int, Object) set(int, E)}
 * method (which is part of the {@link List} interface). Note that the
 * {@code set} method reverses the order of the parameters, to more closely
 * match array usage. Note also that the {@code set} method returns the
 * old value that was stored at the specified position.
 *
 * @param obj what the component is to be set to
 * @param index the specified index
 * @throws ArrayIndexOutOfBoundsException if the index is out of range
 * ({@code index < 0 || index >= size()})
 */
 public synchronized void setElementAt(E obj, int index) {
 
 if (index >= elementCount) {
 
 throw new ArrayIndexOutOfBoundsException(index + " >= " +
 elementCount);
 }
 elementData[index] = obj;
 }
 
 /**
 * Deletes the component at the specified index. Each component in
 * this vector with an index greater or equal to the specified
 * {@code index} is shifted downward to have an index one
 * smaller than the value it had previously. The size of this vector
 * is decreased by {@code 1}.
 *
 * The index must be a value greater than or equal to {@code 0}
 * and less than the current size of the vector.
 *
 * This method is identical in functionality to the {@link #remove(int)}
 * method (which is part of the {@link List} interface). Note that the
 * {@code remove} method returns the old value that was stored at the
 * specified position.
 *
 * @param index the index of the object to remove
 * @throws ArrayIndexOutOfBoundsException if the index is out of range
 * ({@code index < 0 || index >= size()})
 */
 public synchronized void removeElementAt(int index) {
 
 modCount++;
 if (index >= elementCount) {
 
 throw new ArrayIndexOutOfBoundsException(index + " >= " +
 elementCount);
 }
 else if (index < 0) {
 
 throw new ArrayIndexOutOfBoundsException(index);
 }
 int j = elementCount - index - 1;
 // 数组元素的移动
 if (j > 0) {
 
 System.arraycopy(elementData, index + 1, elementData, index, j);
 }
 elementCount--;
 elementData[elementCount] = null; /* to let gc do its work */
 }
 
 /**
 * Inserts the specified object as a component in this vector at the
 * specified {@code index}. Each component in this vector with
 * an index greater or equal to the specified {@code index} is
 * shifted upward to have an index one greater than the value it had
 * previously.
 *
 * The index must be a value greater than or equal to {@code 0}
 * and less than or equal to the current size of the vector. (If the
 * index is equal to the current size of the vector, the new element
 * is appended to the Vector.)
 *
 * This method is identical in functionality to the
 * {@link #add(int, Object) add(int, E)}
 * method (which is part of the {@link List} interface). Note that the
 * {@code add} method reverses the order of the parameters, to more closely
 * match array usage.
 *
 * @param obj the component to insert
 * @param index where to insert the new component
 * @throws ArrayIndexOutOfBoundsException if the index is out of range
 * ({@code index < 0 || index > size()})
 */
 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++;
 }
 
 /**
 * 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.
 *
 * This method is identical in functionality to the
 * {@link #add(Object) add(E)}
 * method (which is part of the {@link List} interface).
 * 直接插入到数组尾部
 * @param obj the component to be added
 */
 public synchronized void addElement(E obj) {
 
 modCount++;
 ensureCapacityHelper(elementCount + 1);
 elementData[elementCount++] = obj;
 }
 
 /**
 * 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.
 *
 * 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;
 }
 
 /**
 * Removes all components from this vector and sets its size to zero.
 *
 * This method is identical in functionality to the {@link #clear}
 * method (which is part of the {@link List} interface).
 */
 public synchronized void removeAllElements() {
 
 modCount++;
 // Let gc do its work
 for (int i = 0; i < elementCount; i++)
 elementData[i] = null;
 
 elementCount = 0;
 }
 
 /**
 * Returns a clone of this vector. The copy will contain a
 * reference to a clone of the internal data array, not a reference
 * to the original internal data array of this {@code Vector} object.
 *
 * @return a clone of this vector
 */
 public synchronized Object clone() {
 
 try {
 
 @SuppressWarnings("unchecked")
 Vector<E> v = (Vector<E>) super.clone();
 v.elementData = Arrays.copyOf(elementData, elementCount);
 v.modCount = 0;
 return v;
 } catch (CloneNotSupportedException e) {
 
 // this shouldn't happen, since we are Cloneable
 throw new InternalError(e);
 }
 }
 
 /**
 * Returns an array containing all of the elements in this Vector
 * in the correct order.
 *
 * @since 1.2
 */
 public synchronized Object[] toArray() {
 
 return Arrays.copyOf(elementData, elementCount);
 }
 
 /**
 * Returns an array containing all of the elements in this Vector in the
 * correct order; the runtime type of the returned array is that of the
 * specified array. If the Vector fits in the specified array, it is
 * returned therein. Otherwise, a new array is allocated with the runtime
 * type of the specified array and the size of this Vector.
 *
 * If the Vector fits in the specified array with room to spare
 * (i.e., the array has more elements than the Vector),
 * the element in the array immediately following the end of the
 * Vector is set to null. (This is useful in determining the length
 * of the Vector only if the caller knows that the Vector
 * does not contain any null elements.)
 *
 * @param a the array into which the elements of the Vector are to
 * be stored, if it is big enough; otherwise, a new array of the
 * same runtime type is allocated for this purpose.
 * @return an array containing the elements of the Vector
 * @throws ArrayStoreException if the runtime type of a is not a supertype
 * of the runtime type of every element in this Vector
 * @throws NullPointerException if the given array is null
 * @since 1.2
 */
 @SuppressWarnings("unchecked")
 public synchronized <T> T[] toArray(T[] a) {
 
 if (a.length < elementCount)
 return (T[]) Arrays.copyOf(elementData, elementCount, a.getClass());
 
 System.arraycopy(elementData, 0, a, 0, elementCount);
 
 if (a.length > elementCount)
 a[elementCount] = null;
 
 return a;
 }
 
 // Positional Access Operations
 
 @SuppressWarnings("unchecked")
 E elementData(int index) {
 
 return (E) elementData[index];
 }
 
 /**
 * 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;
 }
 
 /**
 * 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);
 }
 
 /**
 * Inserts the specified element at the specified position in this Vector.
 * Shifts the element currently at that position (if any) and any
 * subsequent elements to the right (adds one to their indices).
 *
 * @param index index at which the specified element is to be inserted
 * @param element element to be inserted
 * @throws ArrayIndexOutOfBoundsException if the index is out of range
 * ({@code index < 0 || index > size()})
 * @since 1.2
 */
 public void add(int index, E element) {
 
 insertElementAt(element, index);
 }
 }

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[20201205145755.png]: /images/20221119/4306353916b6439ca6ae20ea2d0c35b4.png
[gzh.jpg]: /images/20221119/980d93379e4c4b619305e888fdc4c81d.png