【Java入门提高篇】Day21 Java容器类详解（四）ArrayList源码分析

/** * ArrayList 是List接口的动态数组实现，实现了List的所有可选操作，并且允许所有元素，包括null。 * ArrayList 跟Vector差不多，但它不是线程安全的。 * ArrayList 的容量会根据列表大小自动调整。在添加大量元素之前，可以使用ensureCapacity 方法来保证列表有足够空间存放元素。 * ArrayList 不是线程安全的，所以如果多条线程将要对其进行结构性改变时（如添加删除元素），需要使用synchronized 进行同步。 * 如果不存在这样的对象，则需要使用其同步包装类 Collections.synchronizedList * List list = Collections.synchronizedList(new ArrayList(...)); * * iterator() 方法将会返回一个listIterator，其中的方法是“fail-fast(快速失败的)”，如果在创建了迭代器之后，在用迭代器遍历一个列表时， * 如果遍历过程中对集合对象的内容进行了修改（增加、删除、修改），则会抛出Concurrent Modification Exception。 * 但fail-fast 的行为是无法得到保证的，不可能对是否出现不同步并发修改做出任何硬性保证。 * 快速失败迭代器会尽最大努力抛出 ConcurrentModificationException。 * 因此，为提高这类迭代器的正确性而编写一个依赖于此异常的程序是错误的做法：迭代器的快速失败行为应该仅用于检测 bug。 */ public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable { private static final long serialVersionUID = 8683452581122892189L; /** * 默认容量 */ private static final int DEFAULT_CAPACITY = 10; /** * 空实例共享的空数组 * todo 为什么要区分 EMPTY_ELEMENTDATA 与 DEFAULTCAPACITY_EMPTY_ELEMENTDATA */ private static final Object[] EMPTY_ELEMENTDATA = {}; /** * 默认大小的空实例共享的空数组 */ private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {}; /** * ArrayList的元素存储在其中的数组缓冲区。ArrayList的容量是这个数组缓冲区的长度。 * 当添加第一个元素时，任何为 DEFAULTCAPACITY_EMPTY_ELEMENTDATA 的空ArrayList的容量 * 将扩充到默认大小DEFAULT_CAPACITY（10）。 * 设置为非private 是为了方便内部类进行访问 * * todo 内部动态数组的维护 */ transient Object[] elementData; /** * 列表中实际存储的元素个数 * * todo size 与 capacity */ private int size; /** * 构造一个指定初始容量的空列表 */ public ArrayList(int initialCapacity) { if (initialCapacity > 0) { this.elementData = new Object[initialCapacity]; } else if (initialCapacity == 0) { this.elementData = EMPTY_ELEMENTDATA; } else { throw new IllegalArgumentException("Illegal Capacity: "+ initialCapacity); } } /** * 构造一个默认容量的空列表 */ public ArrayList() { this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA; } /** * 构造一个包含集合C中所有元素的列表，存储顺序为集合C迭代器遍历的顺序 */ public ArrayList(Collection<? extends E> c) { elementData = c.toArray(); if ((size = elementData.length) != 0) { // c.toArray might (incorrectly) not return Object[] (see 6260652) if (elementData.getClass() != Object[].class) elementData = Arrays.copyOf(elementData, size, Object[].class); } else { // replace with empty array. this.elementData = EMPTY_ELEMENTDATA; } } /** * 调整容量大小到列表当前元素个数，以节约存储空间 */ public void trimToSize() { //todo modCount的作用 modCount++; if (size < elementData.length) { elementData = (size == 0) ? EMPTY_ELEMENTDATA : Arrays.copyOf(elementData, size); } } /** * 增加列表容量以确保它至少能容纳指定数量的元素 * * todo 扩容方式 */ public void ensureCapacity(int minCapacity) { //最小扩容量 //如果elementData是空数组则最小扩容量为0，否则最小扩容量为10 int minExpand = (elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA) ? 0 : DEFAULT_CAPACITY; //如果指定的容量比最小扩容量大，则进行扩容操作 if (minCapacity > minExpand) { ensureExplicitCapacity(minCapacity); } } private static int calculateCapacity(Object[] elementData, int minCapacity) { if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) { return Math.max(DEFAULT_CAPACITY, minCapacity); } return minCapacity; } private void ensureCapacityInternal(int minCapacity) { ensureExplicitCapacity(calculateCapacity(elementData, minCapacity)); } private void ensureExplicitCapacity(int minCapacity) { modCount++; // overflow-conscious code if (minCapacity - elementData.length > 0) grow(minCapacity); } /** * 数组容量最大值（- 8 是因为部分 JVM 需要在数组中存入部分头信息） */ private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8; /** * 扩容函数，扩容1.5 倍，扩容后的列表大小在minCapacity与1.5 倍原大小之间取最大值 */ private void grow(int minCapacity) { // overflow-conscious code int oldCapacity = elementData.length; // >> 是右移运算符，作用结果是将原数值的二进制数右移指定位数，转换成十进制的效果 // 就是除以2的指定次方，这里右移一位即除以2 int newCapacity = oldCapacity + (oldCapacity >> 1); if (newCapacity - minCapacity < 0) newCapacity = minCapacity; if (newCapacity - MAX_ARRAY_SIZE > 0) newCapacity = hugeCapacity(minCapacity); // minCapacity is usually close to size, so this is a win: 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; } /** * 元素个数 */ public int size() { return size; } /** * 是否为空 */ public boolean isEmpty() { return size == 0; } /** * 是否包含某个元素 */ public boolean contains(Object o) { return indexOf(o) >= 0; } /** * 查找元素第一次出现的位置 */ public int indexOf(Object o) { if (o == null) { 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; } /** * 查找元素最后一次出现的位置 */ public int lastIndexOf(Object o) { 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; } /** * 返回一个深克隆对象 */ public Object clone() { try { // Object 的克隆方法，复制本对象及其内所有基本类型成员和 String 类型成员 // 但不会复制引用对象 ArrayList<?> v = (ArrayList<?>) super.clone(); v.elementData = Arrays.copyOf(elementData, size); v.modCount = 0; return v; } catch (CloneNotSupportedException e) { // this shouldn't happen, since we are Cloneable throw new InternalError(e); } } /** * 转化成对象数组 */ public Object[] toArray() { return Arrays.copyOf(elementData, size); } /** * 将列表转存到数组a中，如果a的空间足够则直接存放，否则会新建一个数组进行存储 */ @SuppressWarnings("unchecked") public <T> T[] toArray(T[] a) { if (a.length < size) // Make a new array of a's runtime type, but my contents: return (T[]) Arrays.copyOf(elementData, size, a.getClass()); System.arraycopy(elementData, 0, a, 0, size); if (a.length > size) a[size] = null; return a; } // 位置访问操作  @SuppressWarnings("unchecked") E elementData(int index) { return (E) elementData[index]; } /** * 取序号为index的元素 */ public E get(int index) { rangeCheck(index); return elementData(index); } /** * 替换指定位置的元素，并返回原来的元素 */ public E set(int index, E element) { rangeCheck(index); E oldValue = elementData(index); elementData[index] = element; return oldValue; } /** * 添加元素 */ public boolean add(E e) { ensureCapacityInternal(size + 1); // Increments modCount!! elementData[size++] = e; return true; } /** * 插入元素 */ public void add(int index, E element) { rangeCheckForAdd(index); ensureCapacityInternal(size + 1); // Increments modCount!! System.arraycopy(elementData, index, elementData, index + 1, size - index); elementData[index] = element; size++; } /** * 移除指定序号的元素 */ public E remove(int index) { rangeCheck(index); modCount++; E oldValue = elementData(index); int numMoved = size - index - 1; if (numMoved > 0) System.arraycopy(elementData, index+1, elementData, index, numMoved); elementData[--size] = null; // clear to let GC do its work return oldValue; } /** * 移除某个元素 */ 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; } /* * 快速移除 */ private void fastRemove(int index) { modCount++; int numMoved = size - index - 1; if (numMoved > 0) //调用System.arraycopy 进行数组拷贝 //四个参数分别是：待拷贝的数组，原数组的拷贝起始位置，拷贝到的目标数组，目标数组的起始位置 //这里相当于把原数组的一部分拷贝到另一部分，将数组从index+1以后的部分整体往前移一个单位 //将index那个元素覆盖掉 System.arraycopy(elementData, index+1, elementData, index, numMoved); //然后将最后一个元素置为null elementData[--size] = null; // clear to let GC do its work  } /** * 移除所有元素（将所有元素置为null，容量不变） */ public void clear() { modCount++; // clear to let GC do its work for (int i = 0; i < size; i++) elementData[i] = null; size = 0; } /** * 将集合C中的所有元素添加到列表中 */ public boolean addAll(Collection<? extends E> c) { //先将c转换为数组，然后再复制过来 Object[] a = c.toArray(); int numNew = a.length; ensureCapacityInternal(size + numNew); // Increments modCount System.arraycopy(a, 0, elementData, size, numNew); size += numNew; return numNew != 0; } /** * 将集合C中的元素插入指定位置 */ public boolean addAll(int index, Collection<? extends E> c) { rangeCheckForAdd(index); Object[] a = c.toArray(); int numNew = a.length; ensureCapacityInternal(size + numNew); // Increments modCount 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; } /** * 范围性移除，移除列表里序号从fromIndex到toIndex的所有元素，包含fromIndex，不包含toIndex */ protected void removeRange(int fromIndex, int toIndex) { modCount++; int numMoved = size - toIndex; System.arraycopy(elementData, toIndex, elementData, fromIndex, numMoved); // 将其余位置置为null int newSize = size - (toIndex-fromIndex); for (int i = newSize; i < size; i++) { elementData[i] = null; } size = newSize; } /** * 检测index是否超过边界 */ private void rangeCheck(int index) { if (index >= size) throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); } /** * 插入时边界检测 */ private void rangeCheckForAdd(int index) { if (index > size || index < 0) throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); } /** * 生成 IndexOutOfBoundsException 的详细信息 */ private String outOfBoundsMsg(int index) { return "Index: "+index+", Size: "+size; } /** * 移除列表中所有存在于集合c中的元素 */ public boolean removeAll(Collection<?> c) { Objects.requireNonNull(c); return batchRemove(c, false); } /** * 仅保留所有在集合C中的元素 */ public boolean retainAll(Collection<?> c) { Objects.requireNonNull(c); return batchRemove(c, true); } 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 { if (r != size) { System.arraycopy(elementData, r, elementData, w, size - r); w += size - r; } if (w != size) { // clear to let GC do its work for (int i = w; i < size; i++) elementData[i] = null; modCount += size - w; size = w; modified = true; } } return modified; } /** * 将列表实例保存到输出流（即序列化） */ 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(); } } /** * 从输入流中读取列表实例 */ private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException { elementData = EMPTY_ELEMENTDATA; s.defaultReadObject(); s.readInt(); // ignored if (size > 0) { int capacity = calculateCapacity(elementData, size); SharedSecrets.getJavaOISAccess().checkArray(s, Object[].class, capacity); ensureCapacityInternal(size); Object[] a = elementData; // Read in all elements in the proper order. for (int i=0; i<size; i++) { a[i] = s.readObject(); } } } /** * 返回一个从指定序号元素开始的ListIterator */ public ListIterator<E> listIterator(int index) { if (index < 0 || index > size) throw new IndexOutOfBoundsException("Index: "+index); return new ListItr(index); } /** * 返回一个ListIterator */ public ListIterator<E> listIterator() { return new ListItr(0); } /** * 返回一个Iterator */ public Iterator<E> iterator() { return new Itr(); } /** * 优化版本的Iterator * todo 迭代器中modCount的作用 */ 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; Itr() {} 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++]); } // 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(); } } /** * 优化版的ListIterator */ 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(); } } } /** * 获取从 fromIndex 到 toIndex 之间的子集合 * 如果fromIndex == toIndex，则返回的空集合。对该子集合的操作，会影响原有集合。 */ public List<E> subList(int fromIndex, int toIndex) { subListRangeCheck(fromIndex, toIndex, size); return new SubList(this, 0, fromIndex, toIndex); } /** * 检查传入索引的合法性 */ 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 + ")"); } /** * 内部类——子列表 */ 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 != ArrayList.SubList.this.size; } @SuppressWarnings("unchecked") public E next() { checkForComodification(); int i = cursor; if (i >= ArrayList.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 = ArrayList.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++)]); } // update once at end of iteration to reduce heap write traffic 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 { ArrayList.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; ArrayList.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 ArrayList.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 ArrayList.ArrayListSpliterator<E>(ArrayList.this, offset, offset + this.size, this.modCount); } } /** * 遍历 */ @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(); } } /** * 创建一个分割器 */ @Override public Spliterator<E> spliterator() { return new ArrayList.ArrayListSpliterator<>(this, 0, -1, 0); } /** 基于索引的、二分的、懒加载的分割器*/ static final class ArrayListSpliterator<E> implements Spliterator<E> { //用于存放ArrayList对象 private final ArrayList<E> list; //起始位置（包含），advance/split操作时会修改 private int index; //结束位置（不包含），-1 表示到最后一个元素 private int fence; //用于存放list的modCount，当fence被设值后初始化 private int expectedModCount; /** 创建一个范围性的分割器 */ ArrayListSpliterator(ArrayList<E> list, int origin, int fence, int expectedModCount) { this.list = list; // OK if null unless traversed this.index = origin; this.fence = fence; this.expectedModCount = expectedModCount; } //在第一次使用时实例化结束位置 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; } /** * 分割list，返回一个新分割出的spliterator实例，相当于二分法，这个方法会递归 * 1.ArrayListSpliterator本质上还是对原list进行操作，只是通过index和fence来控制每次处理范围 * 2.ArrayListSpliterator在遍历元素时，不能对list进行结构变更操作，否则抛错。 */ public ArrayList.ArrayListSpliterator<E> trySplit() { int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; return (lo >= mid) ? null : // divide range in half unless too small new ArrayList.ArrayListSpliterator<E>(list, lo, index = mid, expectedModCount); } /** * 返回true 时，只表示可能还有元素未处理 * 返回false 时，没有剩余元素需要处理 */ 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; } /** * 顺序遍历处理所有剩下的元素 */ public void forEachRemaining(Consumer<? super E> action) { int i, hi, mc; // hoist accesses and checks from loop 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(); } /** * 估算大小 */ public long estimateSize() { return (long) (getFence() - index); } /** * 获取特征值 */ public int characteristics() { return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED; } } /** * 条件过滤 */ @Override public 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 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(); } // 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  } this.size = newSize; if (modCount != expectedModCount) { throw new ConcurrentModificationException(); } modCount++; } return anyToRemove; } /** * 全部替换 */ @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++; } /** * 用外部比较器来排序 */ @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++; } }