LinkedList源码分析

本文深入解析了LinkedList的底层实现,采用双向循环链表结构,详细介绍了元素的添加与删除过程,对比了与ArrayList的主要区别。

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LinkedList底层实现采用双向循环链表。LinkedList的插入与删除操作都不涉及到元素的移动,改变的只是元素的指向而已。

LinkedList的查找速度是很慢的,因为涉及到元素的逐个获取与比较。

LinkedList与ArrayList的区别,本质上是链表和数组的区别。

import java.util.LinkedList;
import java.util.List;

public class Test2 {
    public static void main(String[] args) {
        List<String> list = new LinkedList<>();
        list.add("a");
    }
}

查看LinkedList的构造方法

/**
     * Constructs an empty list.
     */
    public LinkedList() {
    }

其构造方法内容为空

然后看add方法

/**
     * 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;
    }

查看linkLast(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++;
    }

Node其实就是一个双向链表

private static class Node<E> {
        E item;
        Node<E> next;
        Node<E> prev;

        Node(Node<E> prev, E element, Node<E> next) {
            this.item = element;
            this.next = next;
            this.prev = prev;
        }
    }

这样就实现了添加一个元素。

remove方法

/**
     * Removes the first occurrence of the specified element from this list,
     * if it is present.  If this list does not contain the element, it is
     * unchanged.  More formally, removes the element with the lowest index
     * {@code i} such that
     * <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>
     * (if such an element exists).  Returns {@code true} if this list
     * contained the specified element (or equivalently, if this list
     * changed as a result of the call).
     *
     * @param o element to be removed from this list, if present
     * @return {@code true} if this list contained the specified element
     */
    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;
    }

 

LinkedList是Java中提供的一个双向链表实现类,其内部维护了一个first和last节点,分别表示链表的头和尾。以下是LinkedList源码分析: 1. 声明LinkedList类 ```java public class LinkedList<E> extends AbstractSequentialList<E> implements List<E>, Deque<E>, Cloneable, java.io.Serializable { transient int size = 0; transient Node<E> first; transient Node<E> last; } ``` 2. 声明Node类 ```java private static class Node<E> { E item; Node<E> next; Node<E> prev; Node(Node<E> prev, E element, Node<E> next) { this.item = element; this.next = next; this.prev = prev; } } ``` 3. 实现LinkedList的方法 - add(E e)方法:将元素添加到链表末尾 ```java public boolean add(E e) { linkLast(e); return true; } 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++; } ``` - add(int index, E element)方法:将元素插入到指定位置 ```java public void add(int index, E element) { checkPositionIndex(index); if (index == size) linkLast(element); else linkBefore(element, node(index)); } void linkBefore(E e, Node<E> succ) { final Node<E> pred = succ.prev; final Node<E> newNode = new Node<>(pred, e, succ); succ.prev = newNode; if (pred == null) first = newNode; else pred.next = newNode; size++; } ``` - remove(int index)方法:删除指定位置的元素 ```java public E remove(int index) { checkElementIndex(index); return unlink(node(index)); } E unlink(Node<E> x) { final E element = x.item; final Node<E> next = x.next; final Node<E> prev = x.prev; 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--; return element; } ``` - get(int index)方法:获取指定位置的元素 ```java public E get(int index) { checkElementIndex(index); return node(index).item; } Node<E> node(int 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; } } ``` 以上就是LinkedList源码分析,通过对其源码的分析,我们可以更深入地理解链表的实现。
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