ArrayList 源码解读 基于JDk 1.7.0_80
public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable
ArrayList的底层是使用数组实现的，因为数组的容量是固定的，要实现可变容量List，所以一定存在着容量检测，数组复制等方法。
对象属性
/**
* 默认大小
*/
private static final int DEFAULT_CAPACITY = 10;
/**
* 空对象数组 ，用来做比较
*/
private static final Object[] EMPTY_ELEMENTDATA = {};
/**
* 存储数据的数组
*/
private transient Object[] elementData;
/**
* 大小
*/
private int size;
构造方法
/**
* 指定大小*/
public ArrayList(int initialCapacity) {
super();
if (initialCapacity < 0)
throw new IllegalArgumentException("Illegal Capacity: "+
initialCapacity);
this.elementData = new Object[initialCapacity];
}
/**
* 默认
*/
public ArrayList() {
super();
this.elementData = EMPTY_ELEMENTDATA;
}
/**
* 传入一个Collection*/
public ArrayList(Collection<? extends E> c) {
elementData = c.toArray();
size = elementData.length;
// c.toArray might (incorrectly) not return Object[] (see 6260652)
if (elementData.getClass() != Object[].class)
elementData = Arrays.copyOf(elementData, size, Object[].class);
}
add 方法
public boolean add(E e) {
ensureCapacityInternal(size + 1); // Increments modCount!!
elementData[size++] = e;
return true;
}
// 在指定位置添加对象
public void add(int index, E element) {
// 判断添加的位置是否合理
rangeCheckForAdd(index);
ensureCapacityInternal(size + 1); // Increments modCount!!
System.arraycopy(elementData, index, elementData, index + 1,
size - index);
elementData[index] = element;
size++;
}
//判断是否是空数组
private void ensureCapacityInternal(int minCapacity) {
if (elementData == EMPTY_ELEMENTDATA) {
minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
}
ensureExplicitCapacity(minCapacity);
}
//判断是否达到了数组的容量
private void ensureExplicitCapacity(int minCapacity) {
modCount++;
// overflow-conscious code
if (minCapacity - elementData.length > 0)
grow(minCapacity);
}
//增加容量
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
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);
}
remove 方法
/**
* Removes the element at the specified position in this list.
*/
public E remove(int index) {
// 检测是否越界
rangeCheck(index);
modCount++;
E oldValue = elementData(index);
int numMoved = size - index - 1;
if (numMoved > 0)
//数组移动
System.arraycopy(elementData, index+1, elementData, index,numMoved);
//最后一位设为null
elementData[--size] = null; // clear to let GC do its work
return oldValue;
}
/**
* Removes the first occurrence of the specified element from this list,
*/
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;
}
private void fastRemove(int index) {
modCount++;
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
}
private void rangeCheck(int index) {
if (index >= size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
get方法
public E get(int index) {
rangeCheck(index);
return elementData(index);
}
set方法
public E set(int index, E element) {
rangeCheck(index);
E oldValue = elementData(index);
elementData[index] = element;
return oldValue;
}
内部类Itr 实现了Iterator接口 ，实现了 next() hasNext() remove() 三个方法
public Iterator<E> iterator() { return new Itr();}
/** * An optimized version of AbstractList.Itr */private class Itr implements Iterator<E> { // 下一个返回的位置 int cursor; // index of next element to return // 上次返回的位置 int lastRet = -1; // index of last element returned; -1 if no such int expectedModCount = modCount;
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(); } } //当你在使用迭代器时，不能使用 使用 set add 等方法，改变 存储的数据 final void checkForComodification() { if (modCount != expectedModCount) throw new ConcurrentModificationException(); }}
ListItr 内部类
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();
}
}
}
时间： 2024-07-29 18:43:20