关于集合List的源码分析

private static final int default_capacity = 10;
//arraylist的数组元素存储缓存区，arraylist的长度是这个缓存区的长度，任何elementdata == defaultcapacity_empty_elementdata的空arraylist都将扩展到default_capacity ，并作为第一个元素被添加
transient object[] elementdata;
//默认初始化一个大小为10的object数组
public arraylist() {
        this.elementdata = defaultcapacity_empty_elementdata;
    }

 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);
    }

public class linkedlist<e> extends abstractsequentiallist<e> implements list<e>, deque<e>, cloneable, java.io.serializable
{
   //实现serilizable接口时，将不需要序列化的属性前添加关键字transient，序列化对象的时候，这个属性就不会序列化到指定的目的地中。
    transient int size = 0;
    //指向首节点
    transient node<e> first;
    //指向最后一个节点
    transient node<e> last;
    //构建一个空列表
    public linkedlist() {
    }
    //构建一个包含集合c的列表
    public linkedlist(collection<? extends e> c) {
        this();
        addall(c);
    }
   //将节点值为e的节点作为首节点
    private void linkfirst(e e) {
        final node<e> f = first;
        //构建一个prev值为null,next为f,节点值为e的节点
        final node<e> newnode = new node<>(null, e, f);
        //将newnode作为首节点
        first = newnode;
        //如果newnode后面没有节点就将newnode作为最后一个节点
        if (f == null)
            last = newnode;
        //否则就将newnode赋给其prev
        else
            f.prev = newnode;
        //列表长度加一
        size++;
        modcount++;
    }
    //将节点值为e的节点作为最后一个节点
    void linklast(e e) {
        final node<e> l = last;
      //构建一个prev值为l,next为null,节点值为e的节点
        final node<e> newnode = new node<>(l, e, null);
        last = newnode;
        if (l == null)
            first = newnode;
        else
            l.next = newnode;
        size++;
        modcount++;
    }
    //在非空节点succ之前插入节点e
    void linkbefore(e e, node<e> succ) {
        final node<e> pred = succ.prev;
        //将succ前面的节点和succ作为其prev和next
        final node<e> newnode = new node<>(pred, e, succ);
        //然后将newnode作为succ的prev
        succ.prev = newnode; 
        //如果原来succ是首节点，则将newnode设置为首节点
        if (pred == null)
            first = newnode;
        else
            pred.next = newnode;
        size++;
        modcount++;
    }
     //释放非空的首节点f
    private e unlinkfirst(node<e> f) {
        final e element = f.item;
        final node<e> next = f.next;
        f.item = null;
        f.next = null; // help gc
        //将first节点后面的节点设为首节点
        first = next;
        if (next == null)
            last = null;
        else
            next.prev = null;
        size--;
        modcount++;
        return element;
    }
     //释放非空的尾节点l
       private e unlinklast(node<e> l) {
        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;
    }
    //删除非空节点x
    e unlink(node<e> x) 
    {
        final e element = x.item;
        final node<e> next = x.next;    //x后面的节点
        final node<e> prev = x.prev;    //x前面的节点

        if (prev == null) {
            first = next;
        } else {
            prev.next = next;
            x.prev = null;
        }
        if (next == null) {
            last = prev;
        } else {
            next.prev = prev;
            x.next = null;
        }
        x.item = null;
        size--;
        modcount++;
        return element;
    }
    //返回列表首节点元素值
    public e getfirst() {
        final node<e> f = first;
        if (f == null)
            throw new nosuchelementexception();
        return f.item;
    }
    //返列表尾节点元素值
    public e getlast() {
        final node<e> l = last;
        if (l == null)
            throw new nosuchelementexception();
        return l.item;
    }
    //移除首节点
    public e removefirst() {
        final node<e> f = first;
        if (f == null)
            throw new nosuchelementexception();
        return unlinkfirst(f);
    }
   //删除尾节点
    public e removelast() {
        final node<e> l = last;
        if (l == null)
            throw new nosuchelementexception();
        return unlinklast(l);
    }
  //在列表首部插入节点e
    public void addfirst(e e) {
        linkfirst(e);
    }
    //在列表尾部插入节点e
    public void addlast(e e) {
        linklast(e);
    }
   //判断列表中是否包含有元素o
    public boolean contains(object o) {
        return indexof(o) != -1;
    }
    //返回列表长度大小
    public int size() {
        return size;
    }
    //在列表尾部插入元素
    public boolean add(e e) {
        linklast(e);
        return true;
    }
    //删除元素为o的节点
    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;
    }
   //将集合c中所有元素添加到列表的尾部
    public boolean addall(collection<? extends e> c) {
        return addall(size, c);
    }
   //从指定的位置index开始，将集合c中的元素插入到列表中
    public boolean addall(int index, collection<? extends e> c) {
        //首先判断插入位置的合法性
        checkpositionindex(index);
        object[] a = c.toarray();
        int numnew = a.length;
        if (numnew == 0)
            return false;
        node<e> pred, succ;
        if (index == size) {//说明在列表尾部插入集合元素
            succ = null;
            pred = last;
        } 
        else {  //否则，找到index所在的节点
            succ = node(index);
            pred = succ.prev;
        }
        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;
        }
        if (succ == null) {
            last = pred;
        } else {
            pred.next = succ;
            succ.prev = pred;
        }
        size += numnew;
        modcount++;
        return true;
    }
    //删除列表中所有节点
    public void clear() {
        for (node<e> x = first; x != null; )  
        {
            node<e> next = x.next;
            x.item = null;
            x.next = null;
            x.prev = null;
            x = next;
        }
        first = last = null;
        size = 0;
        modcount++;
    }
    //获取指定索引位置节点的元素值
    public e get(int index) {
        checkelementindex(index);
        return node(index).item;
    }
    //替换指定索引位置节点的元素值
    public e set(int index, e element) {
        checkelementindex(index);
        node<e> x = node(index);
        e oldval = x.item;
        x.item = element;
        return oldval;
    }
    //在指定索引位置之前插入元素e
    public void add(int index, e element) {
        checkpositionindex(index);   
        if (index == size)
            linklast(element);
        else
            linkbefore(element, node(index));
    }
    //删除指定位置的元素
    public e remove(int index) {
        checkelementindex(index);
        return unlink(node(index));
    }
    //判断指定索引位置的元素是否存在
    private boolean iselementindex(int index) {
        return index >= 0 && index < size;
    }
    private boolean ispositionindex(int index) {
        return index >= 0 && index <= size;
    }
    //构建 indexoutofboundsexception详细信息
    private string outofboundsmsg(int index) {
        return "index: "+index+", size: "+size;
    }
    private void checkelementindex(int index) {
        if (!iselementindex(index))
            throw new indexoutofboundsexception(outofboundsmsg(index));
    }
    private void checkpositionindex(int index) {
        if (!ispositionindex(index))
            throw new indexoutofboundsexception(outofboundsmsg(index));
    }
    //返回指定索引位置的节点
    node<e> node(int index) {
        //此处是一个小技巧，当index<size/2时，从列表前半部分开始，否则从后半部分开始
        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;
        }
    }//返回列表中第一次出现o的位置，若不存在则返回-1
    public int indexof(object o) {
        int index = 0;
        if (o == null) {
            for (node<e> x = first; x != null; x = x.next) {
                if (x.item == null)
                    return index;
                index++;
            }
        } else {
            for (node<e> x = first; x != null; x = x.next) {
                if (o.equals(x.item))
                    return index;
                index++;
            }
        }
        return -1;
    }
    //逆向搜索，返回第一出现o的位置，不存在则返回-1
    public int lastindexof(object o) {
        int index = size;
        if (o == null) {
            for (node<e> x = last; x != null; x = x.prev) {
                index--;
                if (x.item == null)
                    return index;
            }
        } else {
            for (node<e> x = last; x != null; x = x.prev) {
                index--;
                if (o.equals(x.item))
                    return index;
            }
        }
        return -1;
    }
   //获取列表首节点元素值
    public e peek() {
        final node<e> f = first;
        return (f == null) ? null : f.item;
    }

    //获取列表首节点元素值，若为空则抛异常
    public e element() {
        return getfirst();
    }
   //检索首节点，若空则返回null,不为空则返回其元素值并删除首节点
    public e poll() {
        final node<e> f = first;
        return (f == null) ? null : unlinkfirst(f);
    }
    //检索首节点，若空则抛异常,不为空则返回其元素值并删除首节点
    public e remove() {
        return removefirst();
    }
   //在列表尾部增加节点e
    public boolean offer(e e) {
        return add(e);
    }
   //在列表首部插入节点e
    public boolean offerfirst(e e) {
        addfirst(e);
        return true;
    }
  //在列表尾部插入节点e
    public boolean offerlast(e e) {
        addlast(e);
        return true;
    }
    public e peekfirst() {
        final node<e> f = first;
        return (f == null) ? null : f.item;
     }
  //获取列表尾节点元素值
    public e peeklast() {
        final node<e> l = last;
        return (l == null) ? null : l.item;
    }
    public e pollfirst() {
        final node<e> f = first;
        return (f == null) ? null : unlinkfirst(f);
    }
    public e polllast() {
        final node<e> l = last;
        return (l == null) ? null : unlinklast(l);
    }
   //入栈
    public void push(e e)
    {
        addfirst(e);
    }
    //出栈
    public e pop() {
        return removefirst();
    }
    //删除列表中第一出现o的节点
    public boolean removefirstoccurrence(object o) {
        return remove(o);
    }
    //逆向搜索，删除第一次出现o的节点
    public boolean removelastoccurrence(object o) {
        if (o == null) {
            for (node<e> x = last; x != null; x = x.prev) {
                if (x.item == null) {
                    unlink(x);
                    return true;
                }
            }
        } else {
            for (node<e> x = last; x != null; x = x.prev) {
                if (o.equals(x.item)) {
                    unlink(x);
                    return true;
                }
            }
        }
        return false;
    }