Java集合分析2
表
[TOC]
表
ArrayList
简介
ArrayList实现了List的接口, 是一个顺序存储的容器, 允许放入null元素,底层通过数组实现, 线程非安全.ArrayList有一个capacity表示容量, 如果在向容器中添加元素且容量不足的时候, 容器会自增大底层数组的大小.
源码剖析
成员变量
//默认的初始化容量
private static final int DEFAULT_CAPACITY = 10;
//空表实例的默认元素
private static final Object[] EMPTY_ELEMENTDATA = {};
//空实例的默认大小空数组. 和上面的EMPTY_ELEMENTDATA甲乙区分是为了当添加第一个元素的时扩容多大.
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
//存储表对象的数组
transient Object[] elementData;
//表的大小
private int size
//最大容量
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
方法分析
//构造函数1
public ArrayList() {
//将内部的数组初始化空数组.
this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}
//构造函数2
public ArrayList(int initialCapacity) {
if (initialCapacity > 0) {
//以initialCapacity初始化数组大小
this.elementData = new Object[initialCapacity];
} else if (initialCapacity == 0) {
//如果传参为0 则初始化一个空数组
this.elementData = EMPTY_ELEMENTDATA;
} else {
// 非法草书抛出异常.
throw new IllegalArgumentException("Illegal Capacity: "+
initialCapacity);
}
}
//构造函数3
//直接使用一个集合初始化一个ArrayList.
public ArrayList(Collection<? extends E> c) {
elementData = c.toArray();
if ((size = elementData.length) != 0) {
// c.toArray might (incorrectly) not return Object[] (see 6260652)
if (elementData.getClass() != Object[].class)
elementData = Arrays.copyOf(elementData, size, Object[].class);
} else {
// replace with empty array.
this.elementData = EMPTY_ELEMENTDATA;
}
}
增删改查
扩容相关函数
// 增大容量来容纳指定数量的元素
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
//新的数组长度是旧数组长度的1.5倍
int newCapacity = oldCapacity + (oldCapacity >> 1);
//如果新的数组长度小于传入参数的最小容量,那么以最小容量为新的数组大小
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
//如果新的数组容量大于了最大数组大小.
//
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
// minCapacity is usually close to size, so this is a win:
//拷贝数组. 最终调用的是System.arrayCopy
elementData = Arrays.copyOf(elementData, newCapacity);
}
//大容量
private static int hugeCapacity(int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
//if 大于最大容量 = Integer.MAX_VALUE
//else 等于最大的数组大小.
return (minCapacity > MAX_ARRAY_SIZE) ?
Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
}
//
private void ensureCapacityInternal(int minCapacity) {
//如果ElementData恒等于默认的空数组.
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
// 取最大的值作为容量.
minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
}
//扩容.
ensureExplicitCapacity(minCapacity);
}
private void ensureExplicitCapacity(int minCapacity) {
modCount++; //更改++
// overflow-conscious code
if (minCapacity - elementData.length > 0)
//如果需求组的容量大于数组的长度, 那么要扩容.
grow(minCapacity);
}
增
//直接增加.
public boolean add(E e) {
//检查容量及扩容
ensureCapacityInternal(size + 1); // Increments modCount!!
//提那家元素
elementData[size++] = e;
//添加成功返回true
return true;
}
//插入
//检查范围
private void rangeCheckForAdd(int index) {
if (index > size || index < 0)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
//
public void add(int index, E element) {
//检查范围
rangeCheckForAdd(index);
//检查容量
ensureCapacityInternal(size + 1); // Increments modCount!!
//拷贝移动数组
System.arraycopy(elementData, index, elementData, index + 1,
size - index);
//向目标位置插入元素
elementData[index] = element;
//size自增
size++;
}
//将一个集合直接添加到ArrayList
public boolean addAll(Collection<? extends E> c) {
//转为数组
Object[] a = c.toArray();
//集合的长度
int numNew = a.length;
// 检查容量
ensureCapacityInternal(size + numNew); // Increments modCount
//拷贝
System.arraycopy(a, 0, elementData, size, numNew);
//size增加numNew
size += numNew;
return numNew != 0;
}
//向指定位置直接插入集合
public boolean addAll(int index, Collection<? extends E> c) {
// 检查范围
rangeCheckForAdd(index);
Object[] a = c.toArray();
int numNew = a.length;
ensureCapacityInternal(size + numNew); // Increments modCount
int numMoved = size - index;
//移动数组
if (numMoved > 0)
System.arraycopy(elementData, index, elementData, index + numNew,
numMoved);
System.arraycopy(a, 0, elementData, index, numNew);
size += numNew;
return numNew != 0;
}
查找
//指定位置索引
public E get(int index) {
rangeCheck(index);
return elementData(index);
}
//直接索引第一个可以找到的对象
public int indexOf(Object o) {
if (o == null) {
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]))
return i;
}
return -1;
}
删除
//直接清除
public void clear() {
modCount++;
//大量的数据并且频繁操作可能引发频繁GC
// clear to let GC do its work
for (int i = 0; i < size; i++)
elementData[i] = null;
size = 0;
}
//删除指定位置元素
public E remove(int index) {
//范围检查
rangeCheck(index);
//操作数自增
modCount++;
// 保存这个被删除的元素 后续会返回
E oldValue = elementData(index);
// 要移动的元素个数
int numMoved = size - index - 1;
//移动元素
if (numMoved > 0)
System.arraycopy(elementData, index+1, elementData, index,
numMoved);
//尾部的元素置null
elementData[--size] = null; // clear to let GC do its work
//将被删除的元素返回
return oldValue;
}
//删除第一个能找到的指定元素
//快速移除, 不检查边界, 并且不返回被移除的对象.
private void fastRemove(int index) {
//修改计数+1;
modCount++;
//计算要移动的数量.
int numMoved = size - index - 1;
if (numMoved > 0)
System.arraycopy(elementData, index+1, elementData, index,
numMoved);
//末尾元素释放.
elementData[--size] = null; // clear to let GC do its work
}
public boolean remove(Object o) {
//如果指定的恒等于null
if (o == null) {
//找到这个null元素
for (int index = 0; index < size; index++)
if (elementData[index] == null) {
//快速移动
fastRemove(index);
return true;
}
} else {
//找到这个非null元素, 并移除
for (int index = 0; index < size; index++)
if (o.equals(elementData[index])) {
fastRemove(index);
return true;
}
}
return false;
}
protected void removeRange(int fromIndex, int toIndex) {
if (ArrayList.this.modCount != this.modCount)
throw new ConcurrentModificationException();
parent.removeRange(parentOffset + fromIndex,
parentOffset + toIndex);
this.modCount = parent.modCount;
this.size -= toIndex - fromIndex;
}
//AbstractList
/*
Overriding this method to take advantage of
* the internals of the list implementation can <i>substantially</i>
* improve the performance of the {@code clear} operation on this list
* and its subLists.
*/
protected void removeRange(int fromIndex, int toIndex) {
ListIterator<E> it = listIterator(fromIndex);
for (int i=0, n=toIndex-fromIndex; i<n; i++) {
it.next();
it.remove();
}
}
//implementation improve the performance
//为什么这个方法是protected 可以参考Effective Java一书中所述.
//TODO 解释为什么
//这个方法是给subList用的
protected void removeRange(int fromIndex, int toIndex) {
// Android-changed: Throw an IOOBE if toIndex < fromIndex as documented.
// All the other cases (negative indices, or indices greater than the size
// will be thrown by System#arrayCopy.
if (toIndex < fromIndex) {
throw new IndexOutOfBoundsException("toIndex < fromIndex");
}
modCount++;
int numMoved = size - toIndex;
System.arraycopy(elementData, toIndex, elementData, fromIndex,
numMoved);
// clear to let GC do its work
int newSize = size - (toIndex-fromIndex);
for (int i = newSize; i < size; i++) {
elementData[i] = null;
}
size = newSize;
}
//移除所有C集合中包括的对象
public boolean removeAll(Collection<?> c) {
//检查非空
Objects.requireNonNull(c);
//
return batchRemove(c, false);
}
//这个方法设计的是在太妙了
private boolean batchRemove(Collection<?> c, boolean complement) {
final Object[] elementData = this.elementData;
int r = 0, w = 0;
boolean modified = false;
try {
for (; r < size; r++)
if (c.contains(elementData[r]) == complement)
//在这里实际上用了个双指针, 将后面的元素移动到被删除的元素上, 这样做的目的是一边删除(占位置)一边移动元素, 效率更高
elementData[w++] = elementData[r];
} finally {
// Preserve behavioral compatibility with AbstractCollection,
// even if c.contains() throws.
//这里可能是为了做一些防御
if (r != size) {
System.arraycopy(elementData, r,
elementData, w,
size - r);
w += size - r;
}
if (w != size) {
// clear to let GC do its work
//将w后续的元素释放
for (int i = w; i < size; i++)
elementData[i] = null;
//修改操作数
modCount += size - w;
//
size = w;
modified = true;
}
}
return modified;
}
//将不属于C中的元素移除.
public boolean retainAll(Collection<?> c) {
Objects.requireNonNull(c);
//参考上述的描述, 这里complement = true, 刚好和removeAll相反.
//这个方法设计的非常巧妙
return batchRemove(c, true);
}
改
//这个没啥说的 非常简单,直接数组赋值就行了,注意不要越界的检查.
public E set(int index, E element) {
if (index >= size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
E oldValue = (E) elementData[index];
elementData[index] = element;
return oldValue;
}
SubList以及迭代器
迭代器
先看几个方法
/**
* Returns an iterator over the elements in this list in proper sequence.
*
* <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
*
* @return an iterator over the elements in this list in proper sequence
*/
public Iterator<E> iterator() {
//返回了Itr实例, 看ArrayList怎么实现的
return new Itr();
}
/**
* An optimized version of AbstractList.Itr
这里说的是一个优化过的AbstractList.Itr
*/
private class Itr implements Iterator<E> {
// Android-changed: Add "limit" field to detect end of iteration.
// The "limit" of this iterator. This is the size of the list at the time the
// iterator was created. Adding & removing elements will invalidate the iteration
// anyway (and cause next() to throw) so saving this value will guarantee that the
// value of hasNext() remains stable and won't flap between true and false when elements
// are added and removed from the list.
protected int limit = ArrayList.this.size; // 迭代器的边界
int cursor; // index of next element to return
int lastRet = -1; // index of last element returned; -1 if no such
int expectedModCount = modCount; //
public boolean hasNext() {
return cursor < limit;
}
@SuppressWarnings("unchecked")
public E next() {
if (modCount != expectedModCount) //如果修改和期望不符, 则抛出多线程修改异常.
throw new ConcurrentModificationException();
int i = cursor;
if (i >= limit) //边界检查
throw new NoSuchElementException();
Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i + 1; //使用cursor增加1
return (E) elementData[lastRet = i];
}
public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
try {
ArrayList.this.remove(lastRet);
cursor = lastRet;
lastRet = -1;
expectedModCount = modCount;
limit--;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
@Override
@SuppressWarnings("unchecked") //foreach的实现
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;
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
/**
* An optimized version of AbstractList.ListItr
优化过的迭代器, 能够前后移动,是一个双向的迭代器,并且支持增删改查.
*/
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() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
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();
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
try {
ArrayList.this.set(lastRet, e);
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
public void add(E e) {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
try {
int i = cursor;
ArrayList.this.add(i, e);
cursor = i + 1;
lastRet = -1;
expectedModCount = modCount;
limit++;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
}
ConcurrentModificationException
在使用迭代器的时候, 经常会遇见一个问题, 困扰大家很久.
举个栗子, 我明明没有在多个线程中修改List 为什么还会出现这个问题呢?
答案是看源码, 最好写一个demo主动报错debug就知道了
fun main() {
val mList = ArrayList<Int>(10)
(1..10).forEach { i ->
mList.add(i)
}
//modCount = 10 对list做了10次add操作
val itr = mList.iterator()
// modCount = expectedModCount = 10
while (itr.hasNext()) {
/**
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];
}
//这里会检查modeCount != expectedModCount
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
*/
val value = itr.next() //
if (value == 5)
mList.remove(value) //此时modeCount = 11
}
}
//或者使用foreach也可以, foreach的底层实现就是iterator
以上的代码就会报错.
分析原因可以参考注释.
主要原因就是在修改ArrayList的时候, 直接使用了ArrayList#remove这种操作, 使得modCount和expectedModCount不再相等, 解决方法就是如果使用迭代器遍历List, 那么在需要修改arrayList的时候, 也使用迭代器, 保证上述两个值始终相等.如下:
fun main() {
val mList = ArrayList<Int>(10)
(1..10).forEach { i ->
mList.add(i)
}
val itr = mList.iterator()
while (itr.hasNext()) {
val value = itr.next()
if (value == 5)
itr.remove()
}
print(mList)
}
SubList
子串就代表的是ArrayList的子List, 上代码.
private class SubList extends AbstractList<E> implements RandomAccess {
private final AbstractList<E> parent; //父List
private final int parentOffset; // 相对父List的偏移
private final int offset; //偏移
int size; // 大小
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;
}
//同ArrayList, 修改的是父List
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;
}
//同上
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);
}
}
LinkedList
链表 ,使用引用(指针)将各个节点串联起来的一种数据结构, 在内存中的存储地址是非连续的.
先看一下LinkedList实现了哪些接口.
public interface Queue<E> extends Collection<E> {
boolean add(E e);
boolean offer(E e);
E remove();
E poll(); //retrieves and remove the head of this queue
E element();// retrieves the head but not remove, throw exception if queue is empty
E peek();// retrieves the head but not remove. not throw exception.
}
public interface Deque<E> extends Queue<E> {
//,,,,
}
public interface List<E> extends Collection<E> {
}
public abstract class AbstractSequentialList<E> extends AbstractList<E> {
}
public class LinkedList<E>
extends AbstractSequentialList<E>
implements List<E>, Deque<E>, Cloneable, java.io.Serializable{
}
节点
private static class Node<E> {
E item; //存储的元素
Node<E> next; //前向
Node<E> prev; //后向
Node(Node<E> prev, E element, Node<E> next) {
this.item = element;
this.next = next;
this.prev = prev;
}
}
成员变量
transient int size = 0; //size 在序列化时不进行序列化
/**
* Pointer to first node.
* Invariant: (first == null && last == null) ||
* (first.prev == null && first.item != null)
*/
transient Node<E> first; //第一个节点
/**
* Pointer to last node.
* Invariant: (first == null && last == null) ||
* (last.next == null && last.item != null)
*/
transient Node<E> last; //最后一个节点.
构造函数
/**
* Constructs an empty list.
*/
public LinkedList() {
}
/**
* Constructs a list containing the elements of the specified
* collection, in the order they are returned by the collection's
* iterator.
*
* @param c the collection whose elements are to be placed into this list
* @throws NullPointerException if the specified collection is null
*/
public LinkedList(Collection<? extends E> c) {
this();
addAll(c);
}
方法分析
增删改查
/**
* Links e as first element.
*/
private void linkFirst(E e) {
final Node<E> f = first;
final Node<E> newNode = new Node<>(null, e, f);
first = newNode;
if (f == null)
last = newNode;
else
f.prev = newNode;
size++;
modCount++;
}
// 将指定的元素插入到list的开头.
public void addFirst(E e) {
linkFirst(e);
}
/**
* Links e as last element.
*/
void linkLast(E e) {
final Node<E> l = last;
final Node<E> newNode = new Node<>(l, e, null);
last = newNode;
if (l == null)
first = newNode;
else
l.next = newNode;
size++;
modCount++;
}
/**
* Appends the specified element to the end of this list.
*
* <p>This method is equivalent to {@link #add}.
*
* @param e the element to add
*/
public void addLast(E e) {
linkLast(e);
}
增
/**
* Appends the specified element to the end of this list.
*
* <p>This method is equivalent to {@link #addLast}.
*
* @param e element to be appended to this list
* @return {@code true} (as specified by {@link Collection#add})
*/
public boolean add(E e) {
linkLast(e);
return true;
}
public boolean addAll(Collection<? extends E> c) {
return addAll(size, c);
}
public boolean addAll(int index, Collection<? extends E> c) {
//位置检查
checkPositionIndex(index);
//将C转换为array
Object[] a = c.toArray();
//a的长度
int numNew = a.length;
if (numNew == 0)
return false;
//两个node
Node<E> pred, succ;
//如果刚好是到尾部, 将pred指向last
if (index == size) {
succ = null;
pred = last;
} else {
//否则在指定的index处插入.
succ = node(index);
pred = succ.prev;
}
//将元素逐个插入到list中
for (Object o : a) {
@SuppressWarnings("unchecked") E e = (E) o;
Node<E> newNode = new Node<>(pred, e, null);
if (pred == null)
first = newNode;
else
pred.next = newNode;
pred = newNode;
}
//如果succ是null则, last=pred (last指向最后一个非空元素)
if (succ == null) {
last = pred;
} else {
//如果succ不为空, 那么将pred和succ连接起来.
pred.next = succ;
succ.prev = pred;
}
//size增加number
size += numNew;
//modCount自增.
modCount++;
return true;
}
//位置检查.
private void checkPositionIndex(int index) {
if (!isPositionIndex(index))
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
/**
* Tells if the argument is the index of a valid position for an
* iterator or an add operation.
*/
private boolean isPositionIndex(int index) {
return index >= 0 && index <= size;
}
删除
//移除首个元素并返回
public E removeFirst() {
final Node<E> f = first;
if (f == null)
//注意first == null会抛出异常
throw new NoSuchElementException();
//详细方法
return unlinkFirst(f);
}
/**
* Unlinks non-null first node f.
* 整个函数将移除头部, 并将头部指向头部的下一个元素.
*/
private E unlinkFirst(Node<E> f) {
// assert f == first && f != null;
final E element = f.item;
final Node<E> next = f.next;
f.item = null;
f.next = null; // help GC
first = next;
if (next == null)
last = null;
else
next.prev = null;
size--;
modCount++;
return element;
}
/**
* Removes and returns the last element from this list.
*
* @return the last element from this list
* @throws NoSuchElementException if this list is empty
*/
//移除末尾元素
public E removeLast() {
final Node<E> l = last;
if (l == null)
//注意last == null会抛出异常
throw new NoSuchElementException();
//详细方法
return unlinkLast(l);
}
/**
* Unlinks non-null last node l.
*/
private E unlinkLast(Node<E> l) {
// assert l == last && l != null;
final E element = l.item;
final Node<E> prev = l.prev;
l.item = null;
l.prev = null; // help GC
last = prev;
if (prev == null)
first = null;
else
prev.next = null;
size--;
modCount++;
return element;
}
/**
* 移除函数.
*/
public boolean remove(Object o) {
if (o == null) {
for (Node<E> x = first; x != null; x = x.next) {
if (x.item == null) {
unlink(x);
return true;
}
}
} else {
for (Node<E> x = first; x != null; x = x.next) {
if (o.equals(x.item)) {
unlink(x);
return true;
}
}
}
return false;
}
/**
* Unlinks non-null node x.
*/
E unlink(Node<E> x) {
// assert x != null;
final E element = x.item; //当前
final Node<E> next = x.next; // 前向节点
final Node<E> prev = x.prev; // 后向节点
if (prev == null) { //边界
first = next;
} else {
prev.next = next;
x.prev = null;
}
if (next == null) { //边界
last = prev;
} else {
next.prev = prev;
x.next = null;
}
x.item = null; // 释放元素
size--; // size自减
modCount++; //修改计数自增
return element;
}
public E remove(int index) {
checkElementIndex(index); //检查index是否在边界之内, 否则抛出数组越界异常.
return unlink(node(index));
}
改
改就一个接口, 直接将制定的index上的元素置为指定的元素
/**
* Replaces the element at the specified position in this list with the
* specified element.
*
* @param index index of the element to replace
* @param element element to be stored at the specified position
* @return the element previously at the specified position
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public E set(int index, E element) {
checkElementIndex(index);
Node<E> x = node(index);
E oldVal = x.item;
x.item = element;
return oldVal;
}
查
/**
* Returns the element at the specified position in this list.
*
* @param index index of the element to return
* @return the element at the specified position in this list
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public E get(int index) {
checkElementIndex(index);
return node(index).item;
}
//注意这里返回是非空的
/**
* Returns the (non-null) Node at the specified element index.
*/
Node<E> node(int index) {
// assert isElementIndex(index);
if (index < (size >> 1)) {
Node<E> x = first;
for (int i = 0; i < index; i++)
x = x.next;
return x;
} else {
Node<E> x = last;
for (int i = size - 1; i > index; i--)
x = x.prev;
return x;
}
}
/**
* Returns {@code true} if this list contains the specified element.
* More formally, returns {@code true} if and only if this list contains
* at least one element {@code e} such that
* <tt>(o==null ? e==null : o.equals(e))</tt>.
*
* @param o element whose presence in this list is to be tested
* @return {@code true} if this list contains the specified element
*/
public boolean contains(Object o) {
return indexOf(o) != -1;
}
//索引指定对象o
public int indexOf(Object o) {
int index = 0;
//如果o是空的, 找到第一个null元素
if (o == null) {
for (Node<E> x = first; x != null; x = x.next) {
if (x.item == null)
return index;
index++;
}
//否则找到和o相等的元素,并返回index.
} else {
for (Node<E> x = first; x != null; x = x.next) {
if (o.equals(x.item))
return index;
index++;
}
}
return -1;
}
一些其他特殊操作
peek 返回链表头但不删除
poll 返回链表且删除元素
offer 将指定元素添加到链表末尾
每个方法都有xxFirst xxLast
此外, 还有类似栈的操作
push添加到表头(入栈)
pop 将表头元素移除(出栈)