标签：style blog http io color os ar java for
Serializable, Cloneable, Iterable<E>, Collection<E>, List<E>, RandomAccess
public boolean add(E e) {
ensureCapacity(size + 1); // Increments modCount!!
elementData[size++] = e;
return true;
} public void add(int index, E element) {
if (index > size || index < 0)
throw new IndexOutOfBoundsException(
"Index: "+index+", Size: "+size);
ensureCapacity(size+1); // Increments modCount!!
System.arraycopy(elementData, index, elementData, index + 1,
size - index); //elementData[index,size) --> elementData[index+1,size+1)
elementData[index] = element;
size++;
}ensureCapacity扩容方法：开始前有对modCount修改操作，实现fast-fail迭代public void ensureCapacity(int minCapacity) {
modCount++;
int oldCapacity = elementData.length;
if (minCapacity > oldCapacity) {
Object oldData[] = elementData;
int newCapacity = (oldCapacity * 3)/2 + 1; //0.5倍扩容策略
if (newCapacity < minCapacity)
newCapacity = minCapacity;
// minCapacity is usually close to size, so this is a win:
elementData = Arrays.copyOf(elementData, newCapacity);
}
}remove方法，移动index+1及其后面元素，并将最后一个元素设置为null，帮助GC回收 public E remove(int index) {
RangeCheck(index);
modCount++;
E oldValue = (E) elementData[index];
int numMoved = size - index - 1;
if (numMoved > 0)
System.arraycopy(elementData, index+1, elementData, index,
numMoved); //elementData[index+1,size) -->elementData[index,size-1)
elementData[--size] = null; // Let gc do its work
return oldValue;
}
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;
}fastRemove是私有方法没有返回old valueprivate void fastRemove(int index) {
modCount++;
int numMoved = size - index - 1;
if (numMoved > 0)
System.arraycopy(elementData, index+1, elementData, index,
numMoved);
elementData[--size] = null; // Let gc do its work
}重写readObject和writeObject进行序列化和反序列化，保证只会序列化实际大小的数组避免空间浪费，可以看到writeObject的时候有fast fail判断private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
// Read in size, and any hidden stuff
s.defaultReadObject();
// Read in array length and allocate array
int arrayLength = s.readInt();
Object[] a = elementData = new Object[arrayLength];
// Read in all elements in the proper order.
for (int i=0; i<size; i++)
a[i] = s.readObject();
} 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 array length
s.writeInt(elementData.length);
// Write out all elements in the proper order.
for (int i=0; i<size; i++)
s.writeObject(elementData[i]);
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
}
hasnext和next方法public boolean hasNext() {
return cursor != size();
}
public E next() {
checkForComodification();
try {
E next = get(cursor);
lastRet = cursor++;
return next;
} catch (IndexOutOfBoundsException e) {
checkForComodification();
throw new NoSuchElementException();
}
}remove方法public void remove() {
if (lastRet == -1)
throw new IllegalStateException();
checkForComodification();
try {
AbstractList.this.remove(lastRet);
if (lastRet < cursor)
cursor--;
lastRet = -1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException e) {
throw new ConcurrentModificationException();
}
}-next和remove方法前都需要调用checkForComodification检验容器是否被修改，若被修改则抛出ConcurrentModificationException
ListIterator通过内部类ListItr来实现，其继承了单向迭代器Itr并实现双向迭代器接口ListIteratorListItr(int index) {
cursor = index;
}
previous和next方法设置lastRet不同，next方法是cursor未加1之前的值，而previous是cursor减1以后的值public boolean hasPrevious() {
return cursor != 0;
}
public E previous() {
checkForComodification();
try {
int i = cursor - 1;
E previous = get(i);
lastRet = cursor = i;
return previous;
} catch (IndexOutOfBoundsException e) {
checkForComodification();
throw new NoSuchElementException();
}
}set方法是在lastRet处修改该元素的值，向前遍历一次previous则为cursor-1，向后遍历一次则为cursorpublic void set(E e) {
if (lastRet == -1)
throw new IllegalStateException();
checkForComodification();
try {
AbstractList.this.set(lastRet, e);
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}add方法在当前cursor位置添加，并将cusor加1public void add(E e) {
checkForComodification();
try {
AbstractList.this.add(cursor++, e);
lastRet = -1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
标签：style blog http io color os ar java for
原文地址：http://blog.csdn.net/changer328/article/details/40620735
