JDK原始碼分析(5)Vector
阿新 • • 發佈:2018-12-20
JDK版本
Vector簡介
/** * The {@code Vector} class implements a growable array of * objects. Like an array, it contains components that can be * accessed using an integer index. However, the size of a * {@code Vector} can grow or shrink as needed to accommodate * adding and removing items after the {@code Vector} has been created. * * <p>Each vector tries to optimize storage management by maintaining a * {@code capacity} and a {@code capacityIncrement}. The * {@code capacity} is always at least as large as the vector * size; it is usually larger because as components are added to the * vector, the vector's storage increases in chunks the size of * {@code capacityIncrement}. An application can increase the * capacity of a vector before inserting a large number of * components; this reduces the amount of incremental reallocation. * * <p><a name="fail-fast"> * The iterators returned by this class's {@link #iterator() iterator} and * {@link #listIterator(int) listIterator} methods are <em>fail-fast</em></a>: * if the vector is structurally modified at any time after the iterator is * created, in any way except through the iterator's own * {@link ListIterator#remove() remove} or * {@link ListIterator#add(Object) add} methods, the iterator will throw a * {@link ConcurrentModificationException}. Thus, in the face of * concurrent modification, the iterator fails quickly and cleanly, rather * than risking arbitrary, non-deterministic behavior at an undetermined * time in the future. The {@link Enumeration Enumerations} returned by * the {@link #elements() elements} method are <em>not</em> fail-fast. * * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed * as it is, generally speaking, impossible to make any hard guarantees in the * presence of unsynchronized concurrent modification. Fail-fast iterators * throw {@code ConcurrentModificationException} on a best-effort basis. * Therefore, it would be wrong to write a program that depended on this * exception for its correctness: <i>the fail-fast behavior of iterators * should be used only to detect bugs.</i> * * <p>As of the Java 2 platform v1.2, this class was retrofitted to * implement the {@link List} interface, making it a member of the * <a href="{@docRoot}/../technotes/guides/collections/index.html"> * Java Collections Framework</a>. Unlike the new collection * implementations, {@code Vector} is synchronized. If a thread-safe * implementation is not needed, it is recommended to use {@link * ArrayList} in place of {@code Vector}. * * @author Lee Boynton * @author Jonathan Payne * @see Collection * @see LinkedList * @since JDK1.0 */
首先,Vector 是一個可增長的陣列(和 ArrayList 類似),能夠用索引直接找到元素,Vector 的容量可增可減
其次,Vector 使用變數 capacity
和 capacityIncrement
來進行容量的管理,關於容量和大小的說法,之前也提到過,容量是最多能夠容納多少元素,而大小是目前容納了多少元素。capacity
指的就是容量,是永遠大於或等於 Vector 的大小的,不過容量通常是大於 Vector 的大小的,因為它擴容的方式有點特殊,下文提及,在插入大量資料之前,最好能進行適當的擴容,避免了再分配的時間浪費
Vector 是執行緒安全的,它所有的方法都加上了 synchronized
原始碼分析
package java.util; public class Vector<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable { //儲存Vector中的資料的陣列 protected Object[] elementData; // 實際資料的長度 protected int elementCount; //容量增長係數 protected int capacityIncrement; /** use serialVersionUID from JDK 1.0.2 for interoperability */ //Vector的版本序號 private static final long serialVersionUID = -2767605614048989439L; // Vector有參建構函式,指定Vector“容量大小”和“增長係數”的建構函式 public Vector(int initialCapacity, int capacityIncrement) { super(); if (initialCapacity < 0) throw new IllegalArgumentException("Illegal Capacity: "+ //新建一個數組,陣列容量是initialCapacity initialCapacity); this.elementData = new Object[initialCapacity]; //設定容量增長係數 this.capacityIncrement = capacityIncrement; } // Vector有參建構函式,容量大小的建構函式 public Vector(int initialCapacity) { this(initialCapacity, 0); } //Vector無參建構函式,預設容量為10 public Vector() { this(10); } //Vector有參建構函式,指定集合的Vector建構函式 public Vector(Collection<? extends E> c) { //獲取“集合(c)”的陣列,並將其賦值給elementData elementData = c.toArray(); //設定陣列長度 elementCount = elementData.length; // c.toArray might (incorrectly) not return Object[] (see 6260652) if (elementData.getClass() != Object[].class) elementData = Arrays.copyOf(elementData, elementCount, Object[].class); } // 將陣列Vector的全部元素都拷貝到陣列anArray中 public synchronized void copyInto(Object[] anArray) { System.arraycopy(elementData, 0, anArray, 0, elementCount); } // 將當前容量值設為 = 實際元素個數 public synchronized void trimToSize() { modCount++; int oldCapacity = elementData.length; if (elementCount < oldCapacity) { elementData = Arrays.copyOf(elementData, elementCount); } } // 確定Vector的容量 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); } //設定最大陣列長度 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; } // 設定容量值為 newSize public synchronized void setSize(int newSize) { modCount++; if (newSize > elementCount) { // 若 "newSize 大於 Vector容量",則調整Vector的大小。 ensureCapacityHelper(newSize); } else { // 若 "newSize 小於/等於 Vector容量",則將newSize位置開始的元素都設定為null for (int i = newSize ; i < elementCount ; i++) { elementData[i] = null; } } elementCount = newSize; } // 返回“Vector的總的容量” public synchronized int capacity() { return elementData.length; } // 返回“Vector的實際大小”,即Vector中元素個數 public synchronized int size() { return elementCount; } // 判斷Vector是否為空 public synchronized boolean isEmpty() { return elementCount == 0; } // 返回“Vector中全部元素對應的Enumeration” public Enumeration<E> elements() { // 通過匿名類實現Enumeration return new Enumeration<E>() { int count = 0; // 是否存在下一個元素 public boolean hasMoreElements() { return count < elementCount; } // 獲取下一個元素 public E nextElement() { synchronized (Vector.this) { if (count < elementCount) { return elementData(count++); } } throw new NoSuchElementException("Vector Enumeration"); } }; } // 返回Vector中是否包含物件(o) 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); } // 從index位置開始向後查詢元素(o)。 // 若找到,則返回元素的索引值;否則,返回-1 public synchronized int indexOf(Object o, int index) { if (o == null) { // 若查詢元素為null,則正向找出null元素,並返回它對應的序號 for (int i = index ; i < elementCount ; i++) if (elementData[i]==null) return i; } else { // 若查詢元素不為null,則正向找出該元素,並返回它對應的序號 for (int i = index ; i < elementCount ; i++) if (o.equals(elementData[i])) return i; } return -1; } // 從後向前查詢元素(o)。並返回元素的索引 public synchronized int lastIndexOf(Object o) { return lastIndexOf(o, elementCount-1); } // 從後向前查詢元素(o)。開始位置是從前向後的第index個數; // 若找到,則返回元素的“索引值”;否則,返回-1。 public synchronized int lastIndexOf(Object o, int index) { if (index >= elementCount) throw new IndexOutOfBoundsException(index + " >= "+ elementCount); if (o == null) { // 若查詢元素為null,則反向找出null元素,並返回它對應的序號 for (int i = index; i >= 0; i--) if (elementData[i]==null) return i; } else { // 若查詢元素不為null,則反向找出該元素,並返回它對應的序號 for (int i = index; i >= 0; i--) if (o.equals(elementData[i])) return i; } return -1; } // 返回Vector中index位置的元素。 // 若index月結,則丟擲異常 public synchronized E elementAt(int index) { if (index >= elementCount) { throw new ArrayIndexOutOfBoundsException(index + " >= " + elementCount); } return elementData(index); } // 獲取Vector中的第一個元素。 // 若失敗,則丟擲異常! public synchronized E firstElement() { if (elementCount == 0) { throw new NoSuchElementException(); } return elementData(0); } // 獲取Vector中的最後一個元素。 // 若失敗,則丟擲異常! public synchronized E lastElement() { if (elementCount == 0) { throw new NoSuchElementException(); } return elementData(elementCount - 1); } // 設定index位置的元素值為obj public synchronized void setElementAt(E obj, int index) { if (index >= elementCount) { throw new ArrayIndexOutOfBoundsException(index + " >= " + elementCount); } elementData[index] = obj; } // 刪除index位置的元素 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; if (j > 0) { System.arraycopy(elementData, index + 1, elementData, index, j); } elementCount--; elementData[elementCount] = null; /* to let gc do its work */ } // 在index位置處插入元素(obj) 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++; } // 將“元素obj”新增到Vector末尾 public synchronized void addElement(E obj) { modCount++; ensureCapacityHelper(elementCount + 1); elementData[elementCount++] = obj; } // 在Vector中查詢並刪除元素obj。 // 成功的話,返回true;否則,返回false。 public synchronized boolean removeElement(Object obj) { modCount++; int i = indexOf(obj); if (i >= 0) { removeElementAt(i); return true; } return false; } // 刪除Vector中的全部元素 public synchronized void removeAllElements() { modCount++; // Let gc do its work // 將Vector中的全部元素設為null for (int i = 0; i < elementCount; i++) elementData[i] = null; elementCount = 0; } //@SuppressWarnings註解用於抑制編譯器產生警告資訊。 // 克隆函式 public synchronized Object clone() { try { @SuppressWarnings("unchecked") Vector<E> v = (Vector<E>) super.clone(); // 將當前Vector的全部元素拷貝到v中 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); } } // 返回Object陣列 public synchronized Object[] toArray() { return Arrays.copyOf(elementData, elementCount); } // 返回Vector的模板陣列。所謂模板陣列,即可以將T設為任意的資料型別 @SuppressWarnings("unchecked") public synchronized <T> T[] toArray(T[] a) { // 若陣列a的大小 < Vector的元素個數; // 則新建一個T[]陣列,陣列大小是“Vector的元素個數”,並將“Vector”全部拷貝到新陣列中 if (a.length < elementCount) return (T[]) Arrays.copyOf(elementData, elementCount, a.getClass()); // 若陣列a的大小 >= Vector的元素個數; // 則將Vector的全部元素都拷貝到陣列a中。 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]; } // 獲取index位置的元素 public synchronized E get(int index) { if (index >= elementCount) throw new ArrayIndexOutOfBoundsException(index); return elementData(index); } // 設定index位置的值為element。並返回index位置的原始值 public synchronized E set(int index, E element) { if (index >= elementCount) throw new ArrayIndexOutOfBoundsException(index); E oldValue = elementData(index); elementData[index] = element; return oldValue; } // 將“元素e”新增到Vector最後。 public synchronized boolean add(E e) { modCount++; ensureCapacityHelper(elementCount + 1); elementData[elementCount++] = e; return true; } // 刪除Vector中的元素o public boolean remove(Object o) { return removeElement(o); } // 在index位置新增元素element public void add(int index, E element) { insertElementAt(element, index); } // 刪除index位置的元素,並返回index位置的原始值 public synchronized E remove(int index) { modCount++; if (index >= elementCount) throw new ArrayIndexOutOfBoundsException(index); E oldValue = elementData(index); int numMoved = elementCount - index - 1; if (numMoved > 0) System.arraycopy(elementData, index+1, elementData, index, numMoved); elementData[--elementCount] = null; // Let gc do its work return oldValue; } // 清空Vector public void clear() { removeAllElements(); } // Bulk Operations // 返回Vector是否包含集合c public synchronized boolean containsAll(Collection<?> c) { return super.containsAll(c); } // 將集合c新增到Vector中 public synchronized boolean addAll(Collection<? extends E> c) { modCount++; Object[] a = c.toArray(); int numNew = a.length; ensureCapacityHelper(elementCount + numNew); // 將集合c的全部元素拷貝到陣列elementData中 System.arraycopy(a, 0, elementData, elementCount, numNew); elementCount += numNew; return numNew != 0; } // 刪除集合c的全部元素 public synchronized boolean removeAll(Collection<?> c) { return super.removeAll(c); } // 刪除“非集合c中的元素” public synchronized boolean retainAll(Collection<?> c) { return super.retainAll(c); } // 從index位置開始,將集合c新增到Vector中 public synchronized boolean addAll(int index, Collection<? extends E> c) { modCount++; if (index < 0 || index > elementCount) throw new ArrayIndexOutOfBoundsException(index); Object[] a = c.toArray(); int numNew = a.length; ensureCapacityHelper(elementCount + numNew); int numMoved = elementCount - index; if (numMoved > 0) System.arraycopy(elementData, index, elementData, index + numNew, numMoved); System.arraycopy(a, 0, elementData, index, numNew); elementCount += numNew; return numNew != 0; } // 返回兩個物件是否相等 public synchronized boolean equals(Object o) { return super.equals(o); } // 計算雜湊值 public synchronized int hashCode() { return super.hashCode(); } // 呼叫父類的toString() public synchronized String toString() { return super.toString(); } // 獲取Vector中fromIndex(包括)到toIndex(不包括)的子集 public synchronized List<E> subList(int fromIndex, int toIndex) { return Collections.synchronizedList(super.subList(fromIndex, toIndex), this); } // 刪除Vector中fromIndex到toIndex的元素 protected synchronized void removeRange(int fromIndex, int toIndex) { modCount++; int numMoved = elementCount - toIndex; System.arraycopy(elementData, toIndex, elementData, fromIndex, numMoved); // Let gc do its work int newElementCount = elementCount - (toIndex-fromIndex); while (elementCount != newElementCount) elementData[--elementCount] = null; } //從檔案中讀取資料,放到Vector中 private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException { ObjectInputStream.GetField gfields = in.readFields(); int count = gfields.get("elementCount", 0); Object[] data = (Object[])gfields.get("elementData", null); if (count < 0 || data == null || count > data.length) { throw new StreamCorruptedException("Inconsistent vector internals"); } elementCount = count; elementData = data.clone(); } // java.io.Serializable的寫入函式 private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException { final java.io.ObjectOutputStream.PutField fields = s.putFields(); final Object[] data; synchronized (this) { fields.put("capacityIncrement", capacityIncrement); fields.put("elementCount", elementCount); data = elementData.clone(); } fields.put("elementData", data); s.writeFields(); } //ListInterator迭代器 public synchronized ListIterator<E> listIterator(int index) { if (index < 0 || index > elementCount) throw new IndexOutOfBoundsException("Index: "+index); return new ListItr(index); } public synchronized ListIterator<E> listIterator() { return new ListItr(0); } //迭代器 public synchronized Iterator<E> iterator() { return new Itr(); } //迭代器內部類 private class Itr implements Iterator<E> { int cursor; // index of next element to return int lastRet = -1; // index of last element returned; -1 if no such int expectedModCount = modCount; public boolean hasNext() { // Racy but within spec, since modifications are checked // within or after synchronization in next/previous return cursor != elementCount; } public E next() { synchronized (Vector.this) { checkForComodification(); int i = cursor; if (i >= elementCount) throw new NoSuchElementException(); cursor = i + 1; return elementData(lastRet = i); } } public void remove() { if (lastRet == -1) throw new IllegalStateException(); synchronized (Vector.this) { checkForComodification(); Vector.this.remove(lastRet); expectedModCount = modCount; } cursor = lastRet; lastRet = -1; } @Override public void forEachRemaining(Consumer<? super E> action) { Objects.requireNonNull(action); synchronized (Vector.this) { final int size = elementCount; int i = cursor; if (i >= size) { return; } @SuppressWarnings("unchecked") final E[] elementData = (E[]) Vector.this.elementData; if (i >= elementData.length) { throw new ConcurrentModificationException(); } while (i != size && modCount == expectedModCount) { action.accept(elementData[i++]); } // update once at end of iteration to reduce heap write traffic cursor = i; lastRet = i - 1; checkForComodification(); } } final void checkForComodification() { if (modCount != expectedModCount) throw new ConcurrentModificationException(); } } /** * An optimized version of AbstractList.ListItr */ final class ListItr extends Itr implements ListIterator<E> { ListItr(int index) { super(); cursor = index; } public boolean hasPrevious() { return cursor != 0; } public int nextIndex() { return cursor; } public int previousIndex() { return cursor - 1; } public E previous() { synchronized (Vector.this) { checkForComodification(); int i = cursor - 1; if (i < 0) throw new NoSuchElementException(); cursor = i; return elementData(lastRet = i); } } public void set(E e) { if (lastRet == -1) throw new IllegalStateException(); synchronized (Vector.this) { checkForComodification(); Vector.this.set(lastRet, e); } } public void add(E e) { int i = cursor; synchronized (Vector.this) { checkForComodification(); Vector.this.add(i, e); expectedModCount = modCount; } cursor = i + 1; lastRet = -1; } } @Override public synchronized void forEach(Consumer<? super E> action) { Objects.requireNonNull(action); final int expectedModCount = modCount; @SuppressWarnings("unchecked") final E[] elementData = (E[]) this.elementData; final int elementCount = this.elementCount; for (int i=0; modCount == expectedModCount && i < elementCount; i++) { action.accept(elementData[i]); } if (modCount != expectedModCount) { throw new ConcurrentModificationException(); } } @Override @SuppressWarnings("unchecked") public synchronized boolean removeIf(Predicate<? super E> filter) { Objects.requireNonNull(filter); // figure out which elements are to be removed // any exception thrown from the filter predicate at this stage // will leave the collection unmodified int removeCount = 0; final int size = elementCount; final BitSet removeSet = new BitSet(size); final int expectedModCount = modCount; for (int i=0; modCount == expectedModCount && i < size; i++) { @SuppressWarnings("unchecked") final E element = (E) elementData[i]; if (filter.test(element)) { removeSet.set(i); removeCount++; } } if (modCount != expectedModCount) { throw new ConcurrentModificationException(); } // shift surviving elements left over the spaces left by removed elements final boolean anyToRemove = removeCount > 0; if (anyToRemove) { final int newSize = size - removeCount; for (int i=0, j=0; (i < size) && (j < newSize); i++, j++) { i = removeSet.nextClearBit(i); elementData[j] = elementData[i]; } for (int k=newSize; k < size; k++) { elementData[k] = null; // Let gc do its work } elementCount = newSize; if (modCount != expectedModCount) { throw new ConcurrentModificationException(); } modCount++; } return anyToRemove; } @Override @SuppressWarnings("unchecked") public synchronized void replaceAll(UnaryOperator<E> operator) { Objects.requireNonNull(operator); final int expectedModCount = modCount; final int size = elementCount; for (int i=0; modCount == expectedModCount && i < size; i++) { elementData[i] = operator.apply((E) elementData[i]); } if (modCount != expectedModCount) { throw new ConcurrentModificationException(); } modCount++; } @SuppressWarnings("unchecked") @Override public synchronized void sort(Comparator<? super E> c) { final int expectedModCount = modCount; Arrays.sort((E[]) elementData, 0, elementCount, c); if (modCount != expectedModCount) { throw new ConcurrentModificationException(); } modCount++; } /** * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em> * and <em>fail-fast</em> {@link Spliterator} over the elements in this * list. * * <p>The {@code Spliterator} reports {@link Spliterator#SIZED}, * {@link Spliterator#SUBSIZED}, and {@link Spliterator#ORDERED}. * Overriding implementations should document the reporting of additional * characteristic values. * * @return a {@code Spliterator} over the elements in this list * @since 1.8 */ @Override public Spliterator<E> spliterator() { return new VectorSpliterator<>(this, null, 0, -1, 0); } /** Similar to ArrayList Spliterator */ static final class VectorSpliterator<E> implements Spliterator<E> { private final Vector<E> list; private Object[] array; private int index; // current index, modified on advance/split private int fence; // -1 until used; then one past last index private int expectedModCount; // initialized when fence set /** Create new spliterator covering the given range */ VectorSpliterator(Vector<E> list, Object[] array, int origin, int fence, int expectedModCount) { this.list = list; this.array = array; this.index = origin; this.fence = fence; this.expectedModCount = expectedModCount; } private int getFence() { // initialize on first use int hi; if ((hi = fence) < 0) { synchronized(list) { array = list.elementData; expectedModCount = list.modCount; hi = fence = list.elementCount; } } return hi; } public Spliterator<E> trySplit() { int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; return (lo >= mid) ? null : new VectorSpliterator<E>(list, array, lo, index = mid, expectedModCount); } @SuppressWarnings("unchecked") public boolean tryAdvance(Consumer<? super E> action) { int i; if (action == null) throw new NullPointerException(); if (getFence() > (i = index)) { index = i + 1; action.accept((E)array[i]); if (list.modCount != expectedModCount) throw new ConcurrentModificationException(); return true; } return false; } @SuppressWarnings("unchecked") public void forEachRemaining(Consumer<? super E> action) { int i, hi; // hoist accesses and checks from loop Vector<E> lst; Object[] a; if (action == null) throw new NullPointerException(); if ((lst = list) != null) { if ((hi = fence) < 0) { synchronized(lst) { expectedModCount = lst.modCount; a = array = lst.elementData; hi = fence = lst.elementCount; } } else a = array; if (a != null && (i = index) >= 0 && (index = hi) <= a.length) { while (i < hi) action.accept((E) a[i++]); if (lst.modCount == expectedModCount) return; } } throw new ConcurrentModificationException(); } public long estimateSize() { return (long) (getFence() - index); } public int characteristics() { return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED; } } }