LinkedList是由一个一个节点连接起来的链表

private static class Node
    
      {        E item;        Node
     
       next;        Node
      
        prev;        Node(Node
       
         prev, E element, Node
        
          next) {            this.item = element;            this.next = next;            this.prev = prev;        }    }
        
       
      
     
    

增

public boolean add(E e) {        linkLast(e);        return true;    }

public void addFirst(E e) {        linkFirst(e);    }    private void linkFirst(E e) {        final Node
    
      f = first;        final Node
     
       newNode = new Node<>(null, e, f);        first = newNode;        if (f == null)            last = newNode;        else            f.prev = newNode;        size++;        modCount++;    }    public void addLast(E e) {        linkLast(e);    }    void linkLast(E e) {        final Node
      
        l = last;        final Node
       
         newNode = new Node<>(l, e, null);        last = newNode;        if (l == null)            first = newNode;        else            l.next = newNode;        size++;        modCount++;    }
       
      
     
    

删

public boolean remove(Object o) {        if (o == null) {            for (Node
    
      x = first; x != null; x = x.next) {                if (x.item == null) {                    unlink(x);                    return true;                }            }        } else {            for (Node
     
       x = first; x != null; x = x.next) {                if (o.equals(x.item)) {                    unlink(x);                    return true;                }            }        }        return false;    }        public E remove(int index) {        checkElementIndex(index);        return unlink(node(index));    }
     
    

改

public E set(int index, E element) {        checkElementIndex(index);        Node
    
      x = node(index);        E oldVal = x.item;        x.item = element;        return oldVal;    }
    

查

public E get(int index) {        checkElementIndex(index);        return node(index).item;    }

其他

// 检索出第一个元素，但不取出    public E peek() {        final Node
    
      f = first;        return (f == null) ? null : f.item;    }    // 检索出第一个元素，同时取出    public E poll() {        final Node
     
       f = first;        return (f == null) ? null : unlinkFirst(f);    }