ArrayList源碼解讀(二)

時間 2019-12-06

原文原文鏈接

clear()刪除錯有緩衝區裏的數據java

public void clear() {
        modCount++;
        final Object[] es = elementData;
        for (int to = size, i = size = 0; i < to; i++)//實際存儲數據置0，從0到實際存儲的位置循環置null
            es[i] = null;
    }

addAll(Collection<? extends E> c)添加集合到當前集合數組

public boolean addAll(Collection<? extends E> c) {
        Object[] a = c.toArray();//轉化爲數組
        modCount++;
        int numNew = a.length;//添加數據長度
        if (numNew == 0)
            return false;//長度爲0直接返回false
        Object[] elementData;
        final int s;
        if (numNew > (elementData = this.elementData).length - (s = size))//舊數據長度+新數據長度大於緩衝區大小，就擴容
            elementData = grow(s + numNew);//擴大爲能夠容納舊數據+新數據大小
        System.arraycopy(a, 0, elementData, s, numNew);//新數據從0位開始複製到緩衝區的s位處，複製長度爲新數據長度
        size = s + numNew;
        return true;
    }

addAll(int index, Collection<? extends E> c)添加集合到當前集合的固定位置安全

public boolean addAll(int index, Collection<? extends E> c) {
        rangeCheckForAdd(index);//確認下標

        Object[] a = c.toArray();//轉數組
        modCount++;
        int numNew = a.length;
        if (numNew == 0)
            return false;//長度爲0直接返回
        Object[] elementData;
        final int s;
        if (numNew > (elementData = this.elementData).length - (s = size))//舊數據長度+新數據長度大於緩衝區大小，就擴容
            elementData = grow(s + numNew);

        int numMoved = s - index;//存儲長度減去index得出就是要移動數據的長度
        if (numMoved > 0)
            System.arraycopy(elementData, index,elementData, index + numNew,numMoved);//把緩衝區從index移動到index + numNew，移動長度爲numMoved 
        System.arraycopy(a, 0, elementData, index, numNew);//把集合從0位移動到緩衝區index位，共移動集合的長度個數據
        size = s + numNew;//實際存儲數更改成size+集合長度
        return true;//返回true
    }

removeRange(int fromIndex, int toIndex)刪除介於(包含)fromIndex和toIndex（不包含）的全部元素app

protected void removeRange(int fromIndex, int toIndex) {
        if (fromIndex > toIndex) {
            throw new IndexOutOfBoundsException(
                    outOfBoundsMsg(fromIndex, toIndex));
        }
        modCount++;
        shiftTailOverGap(elementData, fromIndex, toIndex);
    }

shiftTailOverGap(Object[] es, int lo, int hi)刪除lo(包含)到hi（不包含）期間的元素less

private void shiftTailOverGap(Object[] es, int lo, int hi) {
        System.arraycopy(es, hi, es, lo, size - hi);//從hi位之後的數據複製到lo位，共複製size-hi個數據
        for (int to = size, i = (size -= hi - lo); i < to; i++)
            es[i] = null;//置0
    }

rangeCheckForAdd(int index)判斷是否在區間內dom

private void rangeCheckForAdd(int index) {
        if (index > size || index < 0)
            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
    }

下標越界消息ide

private String outOfBoundsMsg(int index) {
        return "Index: "+index+", Size: "+size;
    }
    
    
private static String outOfBoundsMsg(int fromIndex, int toIndex) {
        return "From Index: " + fromIndex + " > To Index: " + toIndex;
    }

removeAll(Collection<?> c) 刪除緩衝區中，集合包含的數據oop

public boolean removeAll(Collection<?> c) {
        return batchRemove(c, false, 0, size);
    }

retainAll(Collection<?> c)保留緩衝區中，集合包含的數據ui

public boolean retainAll(Collection<?> c) {
        return batchRemove(c, true, 0, size);
    }

batchRemove(Collection<?> c, boolean complement,final int from, final int end)false是刪除傳入集合包含元素，true是保留傳入集合包含元素this

boolean batchRemove(Collection<?> c, boolean complement,
                        final int from, final int end) {
        Objects.requireNonNull(c);
        final Object[] es = elementData;
        int r;
        // Optimize for initial run of survivors
        for (r = from;; r++) {
            if (r == end)//操做長度爲0直接返回false
                return false;
            if (c.contains(es[r]) != complement)//爲true的時候，查找到第一個不保留位r。爲false時候查找到第一個要刪除的位
                break;
        }
        int w = r++;
        try {
            for (Object e; r < end; r++)
                if (c.contains(e = es[r]) == complement)//爲true時把在集合的元素往前移，爲false時，不在集合的元素往前移動
                    es[w++] = e;
        } catch (Throwable ex) {
            // Preserve behavioral compatibility with AbstractCollection,
            // even if c.contains() throws.
            System.arraycopy(es, r, es, w, end - r);
            w += end - r;
            throw ex;
        } finally {
            modCount += end - w;
            shiftTailOverGap(es, w, end);//刪除尾部元素
        }
        return true;
    }

writeObject(java.io.ObjectOutputStream s)輸出對象

private void writeObject(java.io.ObjectOutputStream s)
        throws java.io.IOException {
        // Write out element count, and any hidden stuff
        int expectedModCount = modCount;
        s.defaultWriteObject();

        // Write out size as capacity for behavioral compatibility with clone()
        s.writeInt(size);

        // Write out all elements in the proper order.
        for (int i=0; i<size; i++) {
            s.writeObject(elementData[i]);//循環輸出對象
        }

        if (modCount != expectedModCount) {
            throw new ConcurrentModificationException();//線程安全
        }
    }

readObject(java.io.ObjectInputStream s)讀取對象

private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException {

        // Read in size, and any hidden stuff
        s.defaultReadObject();

        // Read in capacity
        s.readInt(); // ignored

        if (size > 0) {//數據量大於0
            // like clone(), allocate array based upon size not capacity
            SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);
            Object[] elements = new Object[size];

            // Read in all elements in the proper order.
            for (int i = 0; i < size; i++) {
                elements[i] = s.readObject();
            }

            elementData = elements;
        } else if (size == 0) {//數據量等於0
            elementData = EMPTY_ELEMENTDATA;
        } else {
            throw new java.io.InvalidObjectException("Invalid size: " + size);
        }
    }

listIterator()返回迭代器

public ListIterator<E> listIterator() {
        return new ListItr(0);
    }

listIterator(int index)返回迭代器

public ListIterator<E> listIterator(int index) {
        rangeCheckForAdd(index);//
        return new ListItr(index);
    }

Itr內部類

private class Itr implements Iterator<E> {
        int cursor;       // 要返回的下一個元素的索引
        int lastRet = -1; // 返回最後一個元素的索引; 若是沒有這樣的話-1
        int expectedModCount = modCount;

        // prevent creating a synthetic constructor
        Itr() {}

        public boolean hasNext() {
            return cursor != size;
        }

        @SuppressWarnings("unchecked")
        public E next() {
            checkForComodification();//線程安全
            int i = cursor;
            if (i >= size)
                throw new NoSuchElementException();//光標越界
            Object[] elementData = ArrayList.this.elementData;//緩衝區
            if (i >= elementData.length)
                throw new ConcurrentModificationException();//線程不安全
            cursor = i + 1;
            return (E) elementData[lastRet = i];//最後一個元素的索引改爲i
        }

        public void remove() {
            if (lastRet < 0)
                throw new IllegalStateException();
            checkForComodification();

            try {
                ArrayList.this.remove(lastRet);//移除最後返回的元素
                cursor = lastRet;//光標回退
                lastRet = -1;//最後返回的元素被刪除，索引變爲-1
                expectedModCount = modCount;
            } catch (IndexOutOfBoundsException ex) {
                throw new ConcurrentModificationException();
            }
        }

        @Override
        public void forEachRemaining(Consumer<? super E> action) {//循環剩餘
            Objects.requireNonNull(action);
            final int size = ArrayList.this.size;
            int i = cursor;
            if (i < size) {//
                final Object[] es = elementData;
                if (i >= es.length)
                    throw new ConcurrentModificationException();//線程異常
                for (; i < size && modCount == expectedModCount; i++)
                    action.accept(elementAt(es, i));//把緩衝區es中i處元素放進accept方法裏
                // update once at end to reduce heap write traffic
                cursor = i;
                lastRet = i - 1;
                checkForComodification();
            }
        }

        final void checkForComodification() {//線程安全
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
        }
    }

subList(int fromIndex, int toIndex)返回集合的部分（類型變成了SubList）

public List<E> subList(int fromIndex, int toIndex) {
        subListRangeCheck(fromIndex, toIndex, size);
        return new SubList<>(this, fromIndex, toIndex);
    }

ListItr 內部類

private class ListItr extends Itr implements ListIterator<E> {
        ListItr(int index) {
            super();
            cursor = index;
        }

        public boolean hasPrevious() {
            return cursor != 0;
        }

        public int nextIndex() {//下一個索引
            return cursor;
        }

        public int previousIndex() {//前一個索引
            return cursor - 1;
        }

        @SuppressWarnings("unchecked")
        public E previous() {//前一個
            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;//光標前移
            return (E) elementData[lastRet = i];
        }

        public void set(E e) {
            if (lastRet < 0)//最後操做位必須大於0，即進行刪除操做後得滑動索引，否則會報IllegalStateException
                throw new IllegalStateException();
            checkForComodification();

            try {
                ArrayList.this.set(lastRet, e);//最後操做位處插入
            } catch (IndexOutOfBoundsException ex) {
                throw new ConcurrentModificationException();
            }
        }

        public void add(E e) {
            checkForComodification();//線程安全

            try {
                int i = cursor;
                ArrayList.this.add(i, e);//在下一個操做位處添加元素
                cursor = i + 1;//後移光標
                lastRet = -1;//清空最後操做元素
                expectedModCount = modCount;
            } catch (IndexOutOfBoundsException ex) {
                throw new ConcurrentModificationException();
            }
        }
    }

subList(int fromIndex, int toIndex)

public List<E> subList(int fromIndex, int toIndex) {
        subListRangeCheck(fromIndex, toIndex, size);
        return new SubList<>(this, fromIndex, toIndex);
    }

靜態內部類SubList

private static class SubList<E> extends AbstractList<E> implements RandomAccess {
        private final ArrayList<E> root;
        private final SubList<E> parent;
        private final int offset;
        private int size;

        /**
         * Constructs a sublist of an arbitrary ArrayList.
         */
        public SubList(ArrayList<E> root, int fromIndex, int toIndex) {
            this.root = root;
            this.parent = null;
            this.offset = fromIndex;
            this.size = toIndex - fromIndex;
            this.modCount = root.modCount;
        }

        /**
         * Constructs a sublist of another SubList.
         */
        private SubList(SubList<E> parent, int fromIndex, int toIndex) {
            this.root = parent.root;
            this.parent = parent;
            this.offset = parent.offset + fromIndex;
            this.size = toIndex - fromIndex;
            this.modCount = root.modCount;
        }

        public E set(int index, E element) {
            Objects.checkIndex(index, size);
            checkForComodification();
            E oldValue = root.elementData(offset + index);
            root.elementData[offset + index] = element;
            return oldValue;
        }

        public E get(int index) {
            Objects.checkIndex(index, size);
            checkForComodification();
            return root.elementData(offset + index);
        }

        public int size() {
            checkForComodification();
            return size;
        }

        public void add(int index, E element) {
            rangeCheckForAdd(index);
            checkForComodification();
            root.add(offset + index, element);
            updateSizeAndModCount(1);
        }

        public E remove(int index) {
            Objects.checkIndex(index, size);
            checkForComodification();
            E result = root.remove(offset + index);
            updateSizeAndModCount(-1);
            return result;
        }

        protected void removeRange(int fromIndex, int toIndex) {
            checkForComodification();
            root.removeRange(offset + fromIndex, offset + toIndex);
            updateSizeAndModCount(fromIndex - toIndex);
        }

        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();
            root.addAll(offset + index, c);
            updateSizeAndModCount(cSize);
            return true;
        }

        public void replaceAll(UnaryOperator<E> operator) {
            root.replaceAllRange(operator, offset, offset + size);
        }

        public boolean removeAll(Collection<?> c) {
            return batchRemove(c, false);
        }

        public boolean retainAll(Collection<?> c) {
            return batchRemove(c, true);
        }

        private boolean batchRemove(Collection<?> c, boolean complement) {
            checkForComodification();
            int oldSize = root.size;
            boolean modified =
                root.batchRemove(c, complement, offset, offset + size);
            if (modified)
                updateSizeAndModCount(root.size - oldSize);
            return modified;
        }

        public boolean removeIf(Predicate<? super E> filter) {
            checkForComodification();
            int oldSize = root.size;
            boolean modified = root.removeIf(filter, offset, offset + size);
            if (modified)
                updateSizeAndModCount(root.size - oldSize);
            return modified;
        }

        public Object[] toArray() {
            checkForComodification();
            return Arrays.copyOfRange(root.elementData, offset, offset + size);
        }

        @SuppressWarnings("unchecked")
        public <T> T[] toArray(T[] a) {
            checkForComodification();
            if (a.length < size)
                return (T[]) Arrays.copyOfRange(
                        root.elementData, offset, offset + size, a.getClass());
            System.arraycopy(root.elementData, offset, a, 0, size);
            if (a.length > size)
                a[size] = null;
            return a;
        }

        public boolean equals(Object o) {
            if (o == this) {
                return true;
            }

            if (!(o instanceof List)) {
                return false;
            }

            boolean equal = root.equalsRange((List<?>)o, offset, offset + size);
            checkForComodification();
            return equal;
        }

        public int hashCode() {
            int hash = root.hashCodeRange(offset, offset + size);
            checkForComodification();
            return hash;
        }

        public int indexOf(Object o) {
            int index = root.indexOfRange(o, offset, offset + size);
            checkForComodification();
            return index >= 0 ? index - offset : -1;
        }

        public int lastIndexOf(Object o) {
            int index = root.lastIndexOfRange(o, offset, offset + size);
            checkForComodification();
            return index >= 0 ? index - offset : -1;
        }

        public boolean contains(Object o) {
            return indexOf(o) >= 0;
        }

        public Iterator<E> iterator() {
            return listIterator();
        }

        public ListIterator<E> listIterator(int index) {
            checkForComodification();
            rangeCheckForAdd(index);

            return new ListIterator<E>() {
                int cursor = index;
                int lastRet = -1;
                int expectedModCount = root.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 = root.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 = root.elementData;
                    if (offset + i >= elementData.length)
                        throw new ConcurrentModificationException();
                    cursor = i;
                    return (E) elementData[offset + (lastRet = i)];
                }

                public void forEachRemaining(Consumer<? super E> action) {
                    Objects.requireNonNull(action);
                    final int size = SubList.this.size;
                    int i = cursor;
                    if (i < size) {
                        final Object[] es = root.elementData;
                        if (offset + i >= es.length)
                            throw new ConcurrentModificationException();
                        for (; i < size && modCount == expectedModCount; i++)
                            action.accept(elementAt(es, offset + i));
                        // update once at end to reduce heap write traffic
                        cursor = i;
                        lastRet = i - 1;
                        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 = root.modCount;
                    } catch (IndexOutOfBoundsException ex) {
                        throw new ConcurrentModificationException();
                    }
                }

                public void set(E e) {
                    if (lastRet < 0)
                        throw new IllegalStateException();
                    checkForComodification();

                    try {
                        root.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 = root.modCount;
                    } catch (IndexOutOfBoundsException ex) {
                        throw new ConcurrentModificationException();
                    }
                }

                final void checkForComodification() {
                    if (root.modCount != expectedModCount)
                        throw new ConcurrentModificationException();
                }
            };
        }

        public List<E> subList(int fromIndex, int toIndex) {
            subListRangeCheck(fromIndex, toIndex, size);
            return new SubList<>(this, fromIndex, toIndex);
        }

        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 (root.modCount != modCount)
                throw new ConcurrentModificationException();
        }

        private void updateSizeAndModCount(int sizeChange) {
            SubList<E> slist = this;
            do {
                slist.size += sizeChange;
                slist.modCount = root.modCount;
                slist = slist.parent;
            } while (slist != null);
        }

        public Spliterator<E> spliterator() {
            checkForComodification();

            // ArrayListSpliterator not used here due to late-binding
            return new Spliterator<E>() {
                private int index = offset; // current index, modified on advance/split
                private int fence = -1; // -1 until used; then one past last index
                private int expectedModCount; // initialized when fence set

                private int getFence() { // initialize fence to size on first use
                    int hi; // (a specialized variant appears in method forEach)
                    if ((hi = fence) < 0) {
                        expectedModCount = modCount;
                        hi = fence = offset + size;
                    }
                    return hi;
                }

                public ArrayList<E>.ArrayListSpliterator trySplit() {
                    int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
                    // ArrayListSpliterator can be used here as the source is already bound
                    return (lo >= mid) ? null : // divide range in half unless too small
                        root.new ArrayListSpliterator(lo, index = mid, expectedModCount);
                }

                public boolean tryAdvance(Consumer<? super E> action) {
                    Objects.requireNonNull(action);
                    int hi = getFence(), i = index;
                    if (i < hi) {
                        index = i + 1;
                        @SuppressWarnings("unchecked") E e = (E)root.elementData[i];
                        action.accept(e);
                        if (root.modCount != expectedModCount)
                            throw new ConcurrentModificationException();
                        return true;
                    }
                    return false;
                }

                public void forEachRemaining(Consumer<? super E> action) {
                    Objects.requireNonNull(action);
                    int i, hi, mc; // hoist accesses and checks from loop
                    ArrayList<E> lst = root;
                    Object[] a;
                    if ((a = lst.elementData) != null) {
                        if ((hi = fence) < 0) {
                            mc = modCount;
                            hi = offset + 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 getFence() - index;
                }

                public int characteristics() {
                    return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
                }
            };
        }
    }

forEach(Consumer<? super E> action)迭代元素

@Override
    public void forEach(Consumer<? super E> action) {
        Objects.requireNonNull(action);
        final int expectedModCount = modCount;
        final Object[] es = elementData;//緩衝區
        final int size = this.size;
        for (int i = 0; modCount == expectedModCount && i < size; i++)//循環0到實際長度
            action.accept(elementAt(es, i));//對應下標值放入accept方法
        if (modCount != expectedModCount)
            throw new ConcurrentModificationException();//線程安全
    }

spliterator() 返回分裂器

@Override
    public Spliterator<E> spliterator() {
        return new ArrayListSpliterator(0, -1, 0);
    }

內部類ArrayListSpliterator (基於索引的二分裂，懶惰初始化的Spliterator)

final class ArrayListSpliterator implements Spliterator<E> {

        /*
         * If ArrayLists were immutable, or structurally immutable (no
         * adds, removes, etc), we could implement their spliterators
         * with Arrays.spliterator. Instead we detect as much
         * interference during traversal as practical without
         * sacrificing much performance. We rely primarily on
         * modCounts. These are not guaranteed to detect concurrency
         * violations, and are sometimes overly conservative about
         * within-thread interference, but detect enough problems to
         * be worthwhile in practice. To carry this out, we (1) lazily
         * initialize fence and expectedModCount until the latest
         * point that we need to commit to the state we are checking
         * against; thus improving precision.  (This doesn't apply to
         * SubLists, that create spliterators with current non-lazy
         * values).  (2) We perform only a single
         * ConcurrentModificationException check at the end of forEach
         * (the most performance-sensitive method). When using forEach
         * (as opposed to iterators), we can normally only detect
         * interference after actions, not before. Further
         * CME-triggering checks apply to all other possible
         * violations of assumptions for example null or too-small
         * elementData array given its size(), that could only have
         * occurred due to interference.  This allows the inner loop
         * of forEach to run without any further checks, and
         * simplifies lambda-resolution. While this does entail a
         * number of checks, note that in the common case of
         * list.stream().forEach(a), no checks or other computation
         * occur anywhere other than inside forEach itself.  The other
         * less-often-used methods cannot take advantage of most of
         * these streamlinings.
         */

        private int index; // 當前指數，在提早/拆分時修改
        private int fence; // -1直到使用; 而後是最後一個索引
        private int expectedModCount; // 柵欄設置時初始化

        /** 建立覆蓋給定範圍的新分裂器. */
        ArrayListSpliterator(int origin, int fence, int expectedModCount) {
            this.index = origin;
            this.fence = fence;
            this.expectedModCount = expectedModCount;
        }

        private int getFence() { // initialize fence to size on first use
            int hi; // (a specialized variant appears in method forEach)
            if ((hi = fence) < 0) {
                expectedModCount = modCount;
                hi = fence = size;
            }
            return hi;
        }

        public ArrayListSpliterator trySplit() {//拆分
            int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
            return (lo >= mid) ? null : // divide range in half unless too small
                new ArrayListSpliterator(lo, index = mid, expectedModCount);
        }

        public boolean tryAdvance(Consumer<? super E> action) {//迭代，如有下一位返回true
            if (action == null)
                throw new NullPointerException();
            int hi = getFence(), i = index;
            if (i < hi) {
                index = i + 1;
                @SuppressWarnings("unchecked") E e = (E)elementData[i];
                action.accept(e);
                if (modCount != expectedModCount)
                    throw new ConcurrentModificationException();
                return true;
            }
            return false;
        }

        public void forEachRemaining(Consumer<? super E> action) {
            int i, hi, mc; // hoist accesses and checks from loop
            Object[] a;
            if (action == null)
                throw new NullPointerException();
            if ((a = elementData) != null) {
                if ((hi = fence) < 0) {
                    mc = modCount;
                    hi = 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 (modCount == mc)
                        return;
                }
            }
            throw new ConcurrentModificationException();
        }

        public long estimateSize() {
            return getFence() - index;
        }

        public int characteristics() {
            return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
        }
    }

removeIf(Predicate<? super E> filter) 刪除表達式返回true的元素

@Override
    public boolean removeIf(Predicate<? super E> filter) {
        return removeIf(filter, 0, size);
    }

removeIf(Predicate<? super E> filter, int i, final int end)刪除範圍呃逆，表達式返回true的元素

boolean removeIf(Predicate<? super E> filter, int i, final int end) {
        Objects.requireNonNull(filter);
        int expectedModCount = modCount;
        final Object[] es = elementData;//緩衝區
        // Optimize for initial run of survivors
        for (; i < end && !filter.test(elementAt(es, i)); i++)
            ;
        // Tolerate predicates that reentrantly access the collection for
        // read (but writers still get CME), so traverse once to find
        // elements to delete, a second pass to physically expunge.
        if (i < end) {
            final int beg = i;
            final long[] deathRow = nBits(end - beg);
            deathRow[0] = 1L;   // set bit 0
            for (i = beg + 1; i < end; i++)
                if (filter.test(elementAt(es, i)))
                    setBit(deathRow, i - beg);
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
            modCount++;
            int w = beg;
            for (i = beg; i < end; i++)
                if (isClear(deathRow, i - beg))
                    es[w++] = es[i];
            shiftTailOverGap(es, w, end);
            return true;
        } else {
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
            return false;
        }
    }

replaceAll(UnaryOperator<E> operator)替換範圍內元素

@Override
    public void replaceAll(UnaryOperator<E> operator) {
        replaceAllRange(operator, 0, size);
        modCount++;
    }

replaceAllRange(UnaryOperator<E> operator, int i, int end)替換範圍內元素，每一個元素都替換成執行UnaryOperator後的結果

private void replaceAllRange(UnaryOperator<E> operator, int i, int end) {
        Objects.requireNonNull(operator);
        final int expectedModCount = modCount;
        final Object[] es = elementData;
        for (; modCount == expectedModCount && i < end; i++)
            es[i] = operator.apply(elementAt(es, i));
        if (modCount != expectedModCount)
            throw new ConcurrentModificationException();
    }

sort(Comparator<? super E> c)排序集合

public void sort(Comparator<? super E> c) {
        final int expectedModCount = modCount;
        Arrays.sort((E[]) elementData, 0, size, c);//調用Arrays.sort
        if (modCount != expectedModCount)
            throw new ConcurrentModificationException();
        modCount++;
    }

checkInvariants() 檢查不變量

void checkInvariants() {
        // assert size >= 0;
        // assert size == elementData.length || elementData[size] == null;
    }

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