Java源码分析之ArrayList(下)
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package java.util;import java.util.function.Consumer;import java.util.function.Predicate;import java.util.function.UnaryOperator;public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable { //Java的序列化机制是通过在运行时判断类的serialVersionUID来验证版本一致性的 private static final long serialVersionUID = 8683452581122892189L; private static final int DEFAULT_CAPACITY = 10;//默认容量 //空的对象数组(用于new ArrayList(0)的初始化) private static final Object[] EMPTY_ELEMENTDATA = {}; //用于new ArrayList()的初始化 private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {}; transient Object[] elementData;//真正保存数据的数组 不可序列化 private int size;//ArrayList的实际元素数量 public ArrayList(int initialCapacity) {//构造一个具有指定初始容量的空列表 if (initialCapacity > 0) { this.elementData = new Object[initialCapacity]; } else if (initialCapacity == 0) { this.elementData = EMPTY_ELEMENTDATA; } else { throw new IllegalArgumentException("Illegal Capacity: " + initialCapacity); } } public ArrayList() {//无参构造 this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA; } public ArrayList(Collection<? extends E> c) {//构造一个包含指定c元素的列表 elementData = c.toArray(); if ((size = elementData.length) != 0) { //检查类型 if (elementData.getClass() != Object[].class) elementData = Arrays.copyOf(elementData, size, Object[].class); } else { this.elementData = EMPTY_ELEMENTDATA; } } public void trimToSize() {//调整ArrayList的实际容量为size modCount++;//modCount记录修改次数+1 if (size < elementData.length) { elementData = (size == 0) ? EMPTY_ELEMENTDATA : Arrays.copyOf( elementData, size); } } public void ensureCapacity(int minCapacity) { int minExpand = (elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA)? 0 : DEFAULT_CAPACITY; if (minCapacity > minExpand) { ensureExplicitCapacity(minCapacity); } } private void ensureCapacityInternal(int minCapacity) { //如果实际存储数组是空数组 则最小需要容量就是默认容量 if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) { minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity); } ensureExplicitCapacity(minCapacity); } private void ensureExplicitCapacity(int minCapacity) { modCount++; //如果数组（elementData)的长度小于最小需要的容量（minCapacity）就扩容 if (minCapacity - elementData.length > 0) grow(minCapacity); } /* 这个-8是为了减少出错的几率，避免一些机器内存溢出，最大长度依然是Integer.MAX_VALUE 并不是Integer.MAX_VALUE-8(通过hugeCapacity()方法调整) */ private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8; private void grow(int minCapacity) { int oldCapacity = elementData.length; //扩容为原来的1.5倍 int newCapacity = oldCapacity + (oldCapacity >> 1); //如果扩容1.5倍仍小于最小需要容量(针对addAll方法)，就直接扩容为最小需要容量 if (newCapacity - minCapacity < 0) newCapacity = minCapacity; //若超出MAX_ARRAY_SIZE，调用hugeCapacity调整 if (newCapacity - MAX_ARRAY_SIZE > 0) newCapacity = hugeCapacity(minCapacity); //复制元素 elementData = Arrays.copyOf(elementData, newCapacity); } private static int hugeCapacity(int minCapacity) { if (minCapacity < 0) throw new OutOfMemoryError(); return (minCapacity > MAX_ARRAY_SIZE) ? Integer.MAX_VALUE : MAX_ARRAY_SIZE; } public int size() {//返回元素数 return size; } public boolean isEmpty() {//判断列表是否为空 return size == 0; } public boolean contains(Object o) {//判断是否包含指定元素 return indexOf(o) >= 0; } public int indexOf(Object o) {//返回o第一次出现的索引，没有就返回-1 if (o == null) {//判断o是否为null，避免出现o.equals空指针异常 for (int i = 0; i < size; i++) if (elementData[i] == null) return i; } else { for (int i = 0; i < size; i++) if (o.equals(elementData[i])) return i; } return -1; } public int lastIndexOf(Object o) {//返回o最后一次出现的索引，没有就返回-1 if (o == null) { for (int i = size - 1; i >= 0; i--) if (elementData[i] == null) return i; } else { for (int i = size - 1; i >= 0; i--) if (o.equals(elementData[i])) return i; } return -1; } public Object clone() {//浅度复制 try { ArrayList<?> v = (ArrayList<?>) super.clone(); v.elementData = Arrays.copyOf(elementData, size); v.modCount = 0; return v; } catch (CloneNotSupportedException e) { throw new InternalError(e); } } public Object[] toArray() {//集合转换为数组 return Arrays.copyOf(elementData, size); } @SuppressWarnings("unchecked") public <T> T[] toArray(T[] a) {//通过泛型约束返回指定类型的数组 if (a.length < size) return (T[]) Arrays.copyOf(elementData, size, a.getClass()); /* elementData:源数组 0:源数组要复制的起始位置 a:目的数组 0:目的数组要复制的起始位置 size:复制的长度 */ System.arraycopy(elementData, 0, a, 0, size); if (a.length > size) a[size] = null; return a; } @SuppressWarnings("unchecked") E elementData(int index) {//返回数组指定位置元素(没有进行下标检查) return (E) elementData[index]; } public E get(int index) {//返回列表指定位置元素 rangeCheck(index); return elementData(index); } public E set(int index, E element) {//用element替代指定位置上的元素 rangeCheck(index); E oldValue = elementData(index); elementData[index] = element; return oldValue;//返回之前位于index上的元素 } public boolean add(E e) {//在列表尾部添加指定元素 ensureCapacityInternal(size + 1); elementData[size++] = e; return true; } //把element添加到指定位置，当前元素和后续元素(如果有的话)向后移动 public void add(int index, E element) { rangeCheckForAdd(index); ensureCapacityInternal(size + 1); //整体后移 System.arraycopy(elementData, index, elementData, index + 1, size - index); elementData[index] = element; size++; } public E remove(int index) {//移除指定位置元素，向左移动后续元素(如果有的话) rangeCheck(index); modCount++; E oldValue = elementData(index); int numMoved = size - index - 1; if (numMoved > 0)//numMoved=0，移除的是最后一个元素 System.arraycopy(elementData, index + 1, elementData, index, numMoved); elementData[--size] = null; return oldValue;//返回从列表中移除的元素 } //如果集合中有o，则删除第一次出现的并返回true 如果没有，集合不变并返回false public boolean remove(Object o) { if (o == null) { for (int index = 0; index < size; index++) if (elementData[index] == null) { fastRemove(index); return true; } } else { for (int index = 0; index < size; index++) if (o.equals(elementData[index])) { fastRemove(index); return true; } } return false; } private void fastRemove(int index) {//把重复的代码移到一个方法里面 modCount++; int numMoved = size - index - 1; if (numMoved > 0) System.arraycopy(elementData, index + 1, elementData, index, numMoved); elementData[--size] = null; } public void clear() {//移除列表所有元素 modCount++; for (int i = 0; i < size; i++) elementData[i] = null; size = 0; } public boolean addAll(Collection<? extends E> c) {//添加集合c中的所有元素到列表尾部 Object[] a = c.toArray(); int numNew = a.length; ensureCapacityInternal(size + numNew); System.arraycopy(a, 0, elementData, size, numNew); size += numNew; return numNew != 0; } //从指定的位置开始，移动c中的所有元素到列表中，当前元素和后续元素(如果有的话)向右移动 public boolean addAll(int index, Collection<? extends E> c) { rangeCheckForAdd(index); Object[] a = c.toArray(); int numNew = a.length; ensureCapacityInternal(size + numNew); int numMoved = size - index; if (numMoved > 0) System.arraycopy(elementData, index, elementData, index + numNew, numMoved); System.arraycopy(a, 0, elementData, index, numNew); size += numNew; return numNew != 0; } //移除列表中索引在fromIndex(包括)和toIndex(不包括)之间的所有元素 protected void removeRange(int fromIndex, int toIndex) { modCount++; int numMoved = size - toIndex; System.arraycopy(elementData, toIndex, elementData, fromIndex, numMoved); int newSize = size - (toIndex - fromIndex); for (int i = newSize; i < size; i++) { elementData[i] = null; } size = newSize; } private void rangeCheck(int index) {//边界检查 if (index >= size) throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); } private void rangeCheckForAdd(int index) { if (index > size || index < 0) throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); } private String outOfBoundsMsg(int index) { return "Index: " + index + ", Size: " + size; } public boolean removeAll(Collection<?> c) { //传入的参数不为null，返回参数本身，为null，抛出一个空指针异常 Objects.requireNonNull(c); return batchRemove(c, false); } public boolean retainAll(Collection<?> c) { Objects.requireNonNull(c); return batchRemove(c, true); } //beautiful code! private boolean batchRemove(Collection<?> c, boolean complement) { final Object[] elementData = this.elementData; int r = 0, w = 0; boolean modified = false; try { for (; r < size; r++) if (c.contains(elementData[r]) == complement) elementData[w++] = elementData[r]; } finally { //发生了异常，直接把r后面的复制到w后面 if (r != size) { System.arraycopy(elementData, r, elementData, w, size - r); w += size - r; } if (w != size) { //清除多余元素 更好的GC for (int i = w; i < size; i++) elementData[i] = null; modCount += size - w; size = w; modified = true; } } return modified; } private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException { int expectedModCount = modCount; s.defaultWriteObject(); s.writeInt(size); for (int i = 0; i < size; i++) { s.writeObject(elementData[i]); } if (modCount != expectedModCount) { throw new ConcurrentModificationException(); } } private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException { elementData = EMPTY_ELEMENTDATA; s.defaultReadObject(); s.readInt(); if (size > 0) { ensureCapacityInternal(size); Object[] a = elementData; for (int i = 0; i < size; i++) { a[i] = s.readObject(); } } } public ListIterator<E> listIterator(int index) {//得到一个指定位置的迭代器 if (index < 0 || index > size) throw new IndexOutOfBoundsException("Index: " + index); return new ListItr(index); } public ListIterator<E> listIterator() { return new ListItr(0); } public Iterator<E> iterator() { return new Itr(); } private class Itr implements Iterator<E> { int cursor; int lastRet = -1; int expectedModCount = modCount; public boolean hasNext() { return cursor != size; } @SuppressWarnings("unchecked") public E next() { checkForComodification(); int i = cursor; if (i >= size) throw new NoSuchElementException(); Object[] elementData = ArrayList.this.elementData; if (i >= elementData.length) throw new ConcurrentModificationException(); cursor = i + 1; return (E) elementData[lastRet = i]; } public void remove() { if (lastRet < 0) throw new IllegalStateException(); checkForComodification(); try { ArrayList.this.remove(lastRet); cursor = lastRet; lastRet = -1; expectedModCount = modCount; } catch (IndexOutOfBoundsException ex) { throw new ConcurrentModificationException(); } } @Override @SuppressWarnings("unchecked") public void forEachRemaining(Consumer<? super E> consumer) { Objects.requireNonNull(consumer); final int size = ArrayList.this.size; int i = cursor; if (i >= size) { return; } final Object[] elementData = ArrayList.this.elementData; if (i >= elementData.length) { throw new ConcurrentModificationException(); } while (i != size && modCount == expectedModCount) { consumer.accept((E) elementData[i++]); } cursor = i; lastRet = i - 1; checkForComodification(); } final void checkForComodification() { if (modCount != expectedModCount) throw new ConcurrentModificationException(); } } private 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; } @SuppressWarnings("unchecked") public E previous() { checkForComodification(); int i = cursor - 1; if (i < 0) throw new NoSuchElementException(); Object[] elementData = ArrayList.this.elementData; if (i >= elementData.length) throw new ConcurrentModificationException(); cursor = i; return (E) elementData[lastRet = i]; } public void set(E e) { if (lastRet < 0) throw new IllegalStateException(); checkForComodification(); try { ArrayList.this.set(lastRet, e); } catch (IndexOutOfBoundsException ex) { throw new ConcurrentModificationException(); } } public void add(E e) { checkForComodification(); try { int i = cursor; ArrayList.this.add(i, e); cursor = i + 1; lastRet = -1; expectedModCount = modCount; } catch (IndexOutOfBoundsException ex) { throw new ConcurrentModificationException(); } } } public List<E> subList(int fromIndex, int toIndex) { subListRangeCheck(fromIndex, toIndex, size); return new SubList(this, 0, fromIndex, toIndex); } static void subListRangeCheck(int fromIndex, int toIndex, int size) { if (fromIndex < 0) throw new IndexOutOfBoundsException("fromIndex = " + fromIndex); if (toIndex > size) throw new IndexOutOfBoundsException("toIndex = " + toIndex); if (fromIndex > toIndex) throw new IllegalArgumentException("fromIndex(" + fromIndex + ") > toIndex(" + toIndex + ")"); } private class SubList extends AbstractList<E> implements RandomAccess { private final AbstractList<E> parent; private final int parentOffset; private final int offset; int size; SubList(AbstractList<E> parent, int offset, int fromIndex, int toIndex) { this.parent = parent; this.parentOffset = fromIndex; this.offset = offset + fromIndex; this.size = toIndex - fromIndex; this.modCount = ArrayList.this.modCount; } public E set(int index, E e) { rangeCheck(index); checkForComodification(); E oldValue = ArrayList.this.elementData(offset + index); ArrayList.this.elementData[offset + index] = e; return oldValue; } public E get(int index) { rangeCheck(index); checkForComodification(); return ArrayList.this.elementData(offset + index); } public int size() { checkForComodification(); return this.size; } public void add(int index, E e) { rangeCheckForAdd(index); checkForComodification(); parent.add(parentOffset + index, e); this.modCount = parent.modCount; this.size++; } public E remove(int index) { rangeCheck(index); checkForComodification(); E result = parent.remove(parentOffset + index); this.modCount = parent.modCount; this.size--; return result; } protected void removeRange(int fromIndex, int toIndex) { checkForComodification(); parent.removeRange(parentOffset + fromIndex, parentOffset + toIndex); this.modCount = parent.modCount; this.size -= toIndex - fromIndex; } public boolean addAll(Collection<? extends E> c) { return addAll(this.size, c); } public boolean addAll(int index, Collection<? extends E> c) { rangeCheckForAdd(index); int cSize = c.size(); if (cSize == 0) return false; checkForComodification(); parent.addAll(parentOffset + index, c); this.modCount = parent.modCount; this.size += cSize; return true; } public Iterator<E> iterator() { return listIterator(); } public ListIterator<E> listIterator(final int index) { checkForComodification(); rangeCheckForAdd(index); final int offset = this.offset; return new ListIterator<E>() { int cursor = index; int lastRet = -1; int expectedModCount = ArrayList.this.modCount; public boolean hasNext() { return cursor != SubList.this.size; } @SuppressWarnings("unchecked") public E next() { checkForComodification(); int i = cursor; if (i >= SubList.this.size) throw new NoSuchElementException(); Object[] elementData = ArrayList.this.elementData; if (offset + i >= elementData.length) throw new ConcurrentModificationException(); cursor = i + 1; return (E) elementData[offset + (lastRet = i)]; } public boolean hasPrevious() { return cursor != 0; } @SuppressWarnings("unchecked") public E previous() { checkForComodification(); int i = cursor - 1; if (i < 0) throw new NoSuchElementException(); Object[] elementData = ArrayList.this.elementData; if (offset + i >= elementData.length) throw new ConcurrentModificationException(); cursor = i; return (E) elementData[offset + (lastRet = i)]; } @SuppressWarnings("unchecked") public void forEachRemaining(Consumer<? super E> consumer) { Objects.requireNonNull(consumer); final int size = SubList.this.size; int i = cursor; if (i >= size) { return; } final Object[] elementData = ArrayList.this.elementData; if (offset + i >= elementData.length) { throw new ConcurrentModificationException(); } while (i != size && modCount == expectedModCount) { consumer.accept((E) elementData[offset + (i++)]); } lastRet = cursor = i; checkForComodification(); } public int nextIndex() { return cursor; } public int previousIndex() { return cursor - 1; } public void remove() { if (lastRet < 0) throw new IllegalStateException(); checkForComodification(); try { SubList.this.remove(lastRet); cursor = lastRet; lastRet = -1; expectedModCount = ArrayList.this.modCount; } catch (IndexOutOfBoundsException ex) { throw new ConcurrentModificationException(); } } public void set(E e) { if (lastRet < 0) throw new IllegalStateException(); checkForComodification(); try { ArrayList.this.set(offset + lastRet, e); } catch (IndexOutOfBoundsException ex) { throw new ConcurrentModificationException(); } } public void add(E e) { checkForComodification(); try { int i = cursor; SubList.this.add(i, e); cursor = i + 1; lastRet = -1; expectedModCount = ArrayList.this.modCount; } catch (IndexOutOfBoundsException ex) { throw new ConcurrentModificationException(); } } final void checkForComodification() { if (expectedModCount != ArrayList.this.modCount) throw new ConcurrentModificationException(); } }; } public List<E> subList(int fromIndex, int toIndex) { subListRangeCheck(fromIndex, toIndex, size); return new SubList(this, offset, fromIndex, toIndex); } private void rangeCheck(int index) { if (index < 0 || index >= this.size) throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); } private void rangeCheckForAdd(int index) { if (index < 0 || index > this.size) throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); } private String outOfBoundsMsg(int index) { return "Index: " + index + ", Size: " + this.size; } private void checkForComodification() { if (ArrayList.this.modCount != this.modCount) throw new ConcurrentModificationException(); } public Spliterator<E> spliterator() { checkForComodification(); return new ArrayListSpliterator<E>(ArrayList.this, offset, offset + this.size, this.modCount); } } @Override public void forEach(Consumer<? super E> action) { Objects.requireNonNull(action); final int expectedModCount = modCount; @SuppressWarnings("unchecked") final E[] elementData = (E[]) this.elementData; final int size = this.size; for (int i = 0; modCount == expectedModCount && i < size; i++) { action.accept(elementData[i]); } if (modCount != expectedModCount) { throw new ConcurrentModificationException(); } } @Override public Spliterator<E> spliterator() { return new ArrayListSpliterator<>(this, 0, -1, 0); } static final class ArrayListSpliterator<E> implements Spliterator<E> { private final ArrayList<E> list; private int index; private int fence; private int expectedModCount; /** Create new spliterator covering the given range */ ArrayListSpliterator(ArrayList<E> list, int origin, int fence, int expectedModCount) { this.list = list; this.index = origin; this.fence = fence; this.expectedModCount = expectedModCount; } private int getFence() { int hi; ArrayList<E> lst; if ((hi = fence) < 0) { if ((lst = list) == null) hi = fence = 0; else { expectedModCount = lst.modCount; hi = fence = lst.size; } } return hi; } public ArrayListSpliterator<E> trySplit() { int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; return (lo >= mid) ? null : new ArrayListSpliterator<E>(list, lo, index = mid, expectedModCount); } public boolean tryAdvance(Consumer<? super E> action) { if (action == null) throw new NullPointerException(); int hi = getFence(), i = index; if (i < hi) { index = i + 1; @SuppressWarnings("unchecked") E e = (E) list.elementData[i]; action.accept(e); if (list.modCount != expectedModCount) throw new ConcurrentModificationException(); return true; } return false; } public void forEachRemaining(Consumer<? super E> action) { int i, hi, mc; ArrayList<E> lst; Object[] a; if (action == null) throw new NullPointerException(); if ((lst = list) != null && (a = lst.elementData) != null) { if ((hi = fence) < 0) { mc = lst.modCount; hi = lst.size; } else mc = expectedModCount; if ((i = index) >= 0 && (index = hi) <= a.length) { for (; i < hi; ++i) { @SuppressWarnings("unchecked") E e = (E) a[i]; action.accept(e); } if (lst.modCount == mc) return; } } throw new ConcurrentModificationException(); } public long estimateSize() { return (long) (getFence() - index); } public int characteristics() { return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED; } } @Override public boolean removeIf(Predicate<? super E> filter) { Objects.requireNonNull(filter); int removeCount = 0; final BitSet removeSet = new BitSet(size); final int expectedModCount = modCount; final int size = this.size; 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(); } 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; } this.size = newSize; if (modCount != expectedModCount) { throw new ConcurrentModificationException(); } modCount++; } return anyToRemove; } @Override @SuppressWarnings("unchecked") public void replaceAll(UnaryOperator<E> operator) { Objects.requireNonNull(operator); final int expectedModCount = modCount; final int size = this.size; for (int i = 0; modCount == expectedModCount && i < size; i++) { elementData[i] = operator.apply((E) elementData[i]); } if (modCount != expectedModCount) { throw new ConcurrentModificationException(); } modCount++; } @Override @SuppressWarnings("unchecked") public void sort(Comparator<? super E> c) { final int expectedModCount = modCount; Arrays.sort((E[]) elementData, 0, size, c); if (modCount != expectedModCount) { throw new ConcurrentModificationException(); } modCount++; }}阅读全文
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