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ArrayList源码分析(三)-内部类

发布时间:『 2018-04-29 17:08 』  博客类别:Java核心基础  阅读(92) 评论(0)

此章为ArrayList源码最后一章,ArrayList中的内部类:

/**
     * An optimized version of AbstractList.Itr
     * 注意,上一个元素是相对与cursor来说的,cursor指向下一个元素,lastRet其实就是当前元素
     */
    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;  //我们在方法中经常看到modCount,就是为了判断是否有多个线程访问修改
        public boolean hasNext() {
            return cursor != size;
        }
 /**
 * 把ArrayList.this.elementData的数据赋给局部对象数组elementData,返回第i(即当前)个元素
        * cursor指向下一个元素,上一个元素(当前元素)位置lastRet=i
 */
        @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];
        }
 /**
 * 调用ArrayList.this.remove方法,移除上一个元素,让cursor=lastRet,即让cursor=上一个元素
        * 上一个元素=-1,即消除了上一个(当前)元素的索引
        * 感觉有点难说明,最好搭配代码学习,当遍历itertator时,删除当前元素后,
        * 只能在让iterator指向下一个元素iterator.next(),才能继续删除,否则抛出异常
 */
        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();
            }
        }
 /**
 * 可以用lambda表达式遍历iterator
        * 不适用于删除元素,此方法不调用next,并且最后才更改lastRet
 */
        @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();
        }
 
 /**
 * 如果不等于,肯定是有另一个线程对ArrayList进行了修改
 */
        final void checkForComodification() {
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
        }
    }

    /**
     * An optimized version of AbstractList.ListItr
     * 这个类继承了上一个介绍的内部类
     * 除了拥有上一个类的功能,还增加了向前遍历,增加元素,更改元素内容等功能
     */
    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];
        }
 /**
 * 调用ArrayList.this.set更改当前元素内容
 */
        public void set(E e) {
            if (lastRet < 0)
                throw new IllegalStateException();
            checkForComodification();
            try {
                ArrayList.this.set(lastRet, e);
            } catch (IndexOutOfBoundsException ex) {
                throw new ConcurrentModificationException();
            }
        }
 /**
 * 调用ArrayList.this.add增加元素
 * 增加后cursor向后移
 */
        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();
            }
        }
    }
 /**
 * 虽然这个类很长,其实里面的大部分方法调用都是ArrayList中的
 * ListIterator在这个类中采用匿名内部类做了一点更改,不过也很类似
 * 毕竟这个类就是根据ArrayList建一个子集类,就不赘述了
 */
    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++)]);
                    }
                    // 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 {
                        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);
        }
    }

/** Index-based split-by-two, lazily initialized Spliterator */
// 并行迭代我也没玩过,有空再研究一下
    static final class ArrayListSpliterator<E> 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 final ArrayList<E> list;
        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 */
        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;
        }
 
 //返回list的大小(元素个数)
        private int getFence() { // initialize fence to size on first use
            int hi; // (a specialized variant appears in method forEach)
            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 : // divide range in half unless too small
                new ArrayListSpliterator<E>(list, lo, index = mid,
                                            expectedModCount);
        }
 //接收lambda表达式参数,hi>i时,还有元素要处理,返回true
        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;
        }
 //遍历处理元素
        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();
        }
 //判断还有多少元素要处理
        public long estimateSize() {
            return (long) (getFence() - index);
        }
 //不同的特性,可能有优化作用,对计算结果产生影响
        public int characteristics() {
            return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
        }
    }


关键字:   Java     ArrayList     源码  
博主信息
Jim
(生命,是一场徒劳的坚持)