up

util/ArrayList.java

@@ -53,13 +53,15 @@ public void trimToSize() {
  : Arrays.copyOf(elementData, size);
  }
  }
-
+ // 确保容量
  public void ensureCapacity(int minCapacity) {
+ // 确保默认初始化的数组容量是10
  int minExpand = (elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA)
  ? 0
  : DEFAULT_CAPACITY;
-
+ 
  if (minCapacity > minExpand) {
+ // 查看是否需要扩容，如果是则扩容
  ensureExplicitCapacity(minCapacity);
  }
  }
@@ -102,7 +104,7 @@ private static int hugeCapacity(int minCapacity) {
  Integer.MAX_VALUE :
  MAX_ARRAY_SIZE;
  }
-
+ // 返回元素数
  public int size() {
  return size;
  }
@@ -116,13 +118,13 @@ public boolean contains(Object o) {
  }
 
  public int indexOf(Object o) {
- if (o == null) {
+ if (o == null) {// 返回null的索引
  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]))
+ if (o.equals(elementData[i]))// 通过equals判断相等
  return i;
  }
  return -1;
@@ -188,6 +190,7 @@ public E set(int index, E element) {
 
  public boolean add(E e) {
  ensureCapacityInternal(size + 1); // Increments modCount!!
+ // 将元素放入最后一个位置，size++
  elementData[size++] = e;
  return true;
  }
@@ -196,6 +199,8 @@ public void add(int index, E element) {
  rangeCheckForAdd(index);
 
  ensureCapacityInternal(size + 1); // Increments modCount!!
+ // 把要插入的索引之后的元素，全部后移一位，同样有copy低效的问题，如果在比较
+ // 靠前的位置
  System.arraycopy(elementData, index, elementData, index + 1,
  size - index);
  elementData[index] = element;
@@ -245,10 +250,10 @@ private void fastRemove(int index) {
 
  public void clear() {
  modCount++;
-
+ // 所有元素为null
  for (int i = 0; i < size; i++)
  elementData[i] = null;
-
+ // size清零
  size = 0;
  }
 
@@ -290,17 +295,17 @@ protected void removeRange(int fromIndex, int toIndex) {
  }
  size = newSize;
  }
-
+ // 检测索引下标是否越界
  private void rangeCheck(int index) {
  if (index >= size)
  throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
  }
-
+ // add操作的下标越界检查
  private void rangeCheckForAdd(int index) {
  if (index > size || index < 0)
  throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
  }
-
+ // 构成索引下标越界的异常信息
  private String outOfBoundsMsg(int index) {
  return "Index: "+index+", Size: "+size;
  }
@@ -384,43 +389,45 @@ public ListIterator<E> listIterator(int index) {
  public ListIterator<E> listIterator() {
  return new ListItr(0);
  }
-
+ // 返回迭代器实例
  public Iterator<E> iterator() {
  return new Itr();
  }
-
+ // 迭代器的实现
  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;
+ int cursor; // 当前指针
+ int lastRet = -1; // 最后一次位置的指针
+ int expectedModCount = modCount;// 保存一个modCount的副本
 
  public boolean hasNext() {
- return cursor != size;
+ return cursor != size;// 如果当前指针不等于元素数，说明还有元素没有迭代
  }
 
  @SuppressWarnings("unchecked")
  public E next() {
- checkForComodification();
- int i = cursor;
- if (i >= size)
+ checkForComodification();// 并发修改检测
+ int i = cursor;// 把当前指针保存一个副本
+ if (i >= size)// 检测当前指针是否超出了size
  throw new NoSuchElementException();
- Object[] elementData = ArrayList.this.elementData;
+ Object[] elementData = ArrayList.this.elementData;// 一个指向外层元素数组的引用
  if (i >= elementData.length)
  throw new ConcurrentModificationException();
+ // 当前指针前移
  cursor = i + 1;
  return (E) elementData[lastRet = i];
  }
 
  public void remove() {
+ // 状态判断
  if (lastRet < 0)
  throw new IllegalStateException();
- checkForComodification();
+ checkForComodification();// 并发修改检测
 
  try {
- ArrayList.this.remove(lastRet);
- cursor = lastRet;
- lastRet = -1;
- expectedModCount = modCount;
+ ArrayList.this.remove(lastRet);// 调用外层方法，删除lastRet位的元素
+ cursor = lastRet;// 指向下一个元素
+ lastRet = -1;// 防止重复删除
+ expectedModCount = modCount;// expectedModCount重新复制，防止并发修改异常
  } catch (IndexOutOfBoundsException ex) {
  throw new ConcurrentModificationException();
  }
@@ -446,14 +453,15 @@ public void forEachRemaining(Consumer<? super E> consumer) {
  lastRet = i - 1;
  checkForComodification();
  }
-
+ // 检查是否存在并发修改
  final void checkForComodification() {
  if (modCount != expectedModCount)
  throw new ConcurrentModificationException();
  }
  }
-
+ // List迭代器
  private class ListItr extends Itr implements ListIterator<E> {
+ // 迭代索引开始位置
  ListItr(int index) {
  super();
  cursor = index;
@@ -472,9 +480,10 @@ public int previousIndex() {
  }
 
  @SuppressWarnings("unchecked")
+ // 往前迭代
  public E previous() {
  checkForComodification();
- int i = cursor - 1;
+ int i = cursor - 1;// 前移
  if (i < 0)
  throw new NoSuchElementException();
  Object[] elementData = ArrayList.this.elementData;
@@ -755,14 +764,18 @@ public Spliterator<E> spliterator() {
  offset + this.size, this.modCount);
  }
  }
-
+ // 迭代ArrayList的方法
  @Override
  public void forEach(Consumer<? super E> action) {
- Objects.requireNonNull(action);
- final int expectedModCount = modCount;
+ Objects.requireNonNull(action); // 如果action为空抛出空指针异常
+ final int expectedModCount = modCount;// 取得当前的操作计数
  @SuppressWarnings("unchecked")
  final E[] elementData = (E[]) this.elementData;
  final int size = this.size;
+ // modCount == expectedModCount 用来测试是否有并发修改
+ // 如果有人在当前迭代对象上调用了方法，这个这个方法又modCount++
+ // 那么modCount != expectedModCount 
+ // 会抛出ConcurrentModificationException异常
  for (int i=0; modCount == expectedModCount && i < size; i++) {
  action.accept(elementData[i]);
  }