Java系列-LinkedList源码

1.双链表结构

public class LinkedList
    extends AbstractSequentialList
    implements List, Deque, Cloneable, java.io.Serializable{
    transient int size = 0;

    transient Node first;

    transient Node last;

    public LinkedList() {
    }
}

2.add

创建Node

更新last

更新老last的next

public class LinkedList
    extends AbstractSequentialList
    implements List, Deque, Cloneable, java.io.Serializable{
    public boolean add(E e) {
        linkLast(e);
        return true;
    }

    void linkLast(E e) {
        final Node l = last;
        //创建Node
        //prev是last，next是null
        final Node newNode = new Node<>(l, e, null);
        last = newNode; //更新last
        if (l == null){//如果之前没有元素
            first = newNode; //头也是新元素
        } else{
            l.next = newNode;
        }
        size++; //更新个数
        modCount++;
    }

    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;
        }
    }
}
    

3.get

遍历的方式获得元素

public class LinkedList
    extends AbstractSequentialList
    implements List, Deque, Cloneable, java.io.Serializable{
    public E get(int index) {
        checkElementIndex(index); //判断index是否为有效范围内的index
        return node(index).item;
    }

    Node node(int index) {
        // assert isElementIndex(index);

        if (index < (size >> 1)) {//如果index小于size的一半，从first开始遍历
            Node x = first;
            for (int i = 0; i < index; i++){
                x = x.next;
            }
            return x;
        } else {
            Node x = last; //不然从尾开始遍历
            for (int i = size - 1; i > index; i--){
                x = x.prev;
            }
            return x;
        }
    }
}
    

4.remove index

先通过遍历的方式获得元素

然后将该元素从列表移除

public class LinkedList
    extends AbstractSequentialList
    implements List, Deque, Cloneable, java.io.Serializable{

    public E remove(int index) {
        checkElementIndex(index);
        //node(index)找到index位置的node
        return unlink(node(index));
    }

    //将找到的node从链表移除
    E unlink(Node x) {
        // assert x != null;
        final E element = x.item;
        final Node next = x.next;
        final Node prev = x.prev;

        if (prev == null) {//表示找到的元素为第一个元素
            first = next;
        } else {
            prev.next = next; //prev node next 移除node
            x.prev = null;//把这个元素的prev赋值为null
        }

        if (next == null) {//找到的元素为最后一个元素
            last = prev;
        } else {
            next.prev = prev;
            x.next = null; //把这个元素的next赋值为null
        }

        x.item = null; //把这个元素的item赋值为null
        size--;
        modCount++;
        return element;
    }
}
    

5.remove object移除元素

遍历找到元素后，移动该元素

public class LinkedList
    extends AbstractSequentialList
    implements List, Deque, Cloneable, java.io.Serializable{

    public boolean remove(Object o) {
        if (o == null) {
            for (Node x = first; x != null; x = x.next) {
                if (x.item == null) {
                    unlink(x); //移除元素
                    return true;
                }
            }
        } else {
            for (Node x = first; x != null; x = x.next) {
                if (o.equals(x.item)) {
                    unlink(x);
                    return true;
                }
            }
        }
        return false;
    }
}