Share the source code of several common methods in ArrayList-javaTutorial-php.cn

Share the source code of several common methods in ArrayList

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Release： 2017-06-28 09:41:47

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## The above explains the relevant# The source code of several common methods in ##ArrayList

- "Source code analysis of common methods in ArrayList", this article will briefly describe the common methods in LinkedList Parse . LinkedList

is implemented based on a linked list

, which means that it has the advantages and disadvantages of a linked list, with slow random access and fast insertion and deletion speeds. Since it is a linked list, it has a node data structure, and there is no problem of capacity. Just add one at the end.

//LinkedList$Nodeprivate 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;
    }
}

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The first constructor that takes no parameters by default constructs an empty linked list.

//1.LinkedList，默认构造方法public LinkedList() {
}

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The second constructor can pass a collection as a parameter, and the elements in the collection need to be a subclass of

LinkedList

//2.LinkedList，能将一个集合作为参数的构造方法public LinkedList(Collection<? extends E> c) {this();
    addAll(c);
}

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The two construction methods are relatively simple. Next, let’s look at the insertion and deletion of elements.

public boolean add(E e) {
    linkLast(e);    //将元素添加到链表尾部return true;
}

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//LinkedList#linkLastvoid linkLast(E e) {final Node<E> l = last;    //链表尾指针引用暂存final Node<E> newNode = new Node<>(l, e, null);    //构造新节点last = newNode;    //将链表的尾指针指向新节点if (l == null)    //此时为第一次插入元素first = newNode;elsel.next = newNode;    
    size++;    //链表数据总数+1modCount++;    //modCount变量在《有关ArrayList常用方法的源码解析》提到过，增删都会+1，防止一个线程在用迭代器遍历的时候，另一个线程在对其进行修改。}

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Students who have studied "Data Structure" believe that the operation of linked lists will not be unfamiliar. Let's take a look at deleting elements at specified positions

remove(int)

method.

//LinkedList#removepublic E remove(int index) {
    checkElementIndex(index);    //检查是否越界 index >= 0 && index <= sizereturn unlink(node(index));    //调用node方法查找并返回指定索引位置的Node节点}

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//LinkedList#node，根据索引位置返回Node节点Node<E> node(int index) {if (index < (size >> 1)) {    //size >> 1 = size / 2，如果索引位于链表前半部分，则移动fisrt头指针进行查找Node<E> x = first;for (int i = 0; i < index; i++)
            x = x.next;return x;
    } else {    //如果索引位于链表后半部分，则移动last尾指针进行查找Node<E> x = last;for (int i = size - 1; i > index; i--)
            x = x.prev;return x;
    }
}

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Find the

index

position After ##Node, call the unlink method to remove the node.

//LinkedList#unlink，一看即懂E unlink(Node<E> x) {// assert x != null;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--;
    modCount++;return element;
}

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You can see the advantages and disadvantages of

LinkedList

and ArrayList from the code, since only a simple linked list data structure is involved, other methods will not be parsed.

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