[英]Implement doubly linked list
I've looked around on this forum regarding the implementation of doubly linked lists and I can't a grasp of the below code.我在这个论坛上环顾四周关于双向链表的实现,但我无法理解下面的代码。
// instance variables of the DoublyLinkedList
private final Node<E> header; // header sentinel
private final Node<E> trailer; // trailer sentinel
private int size = 0; // number of elements in the list
private int modCount = 0; // number of modifications to the list (adds or removes)
/**
* Creates both elements which act as sentinels
*/
public DoublyLinkedList() {
header = new Node<>(null, null, null); // create header
trailer = new Node<>(null, header, null); // trailer is preceded by header
header.setNext(trailer); // header is followed by trailer
}
I've seen videos about linked lists and doubly ones, but I haven't seen this kind of implementation.我看过关于链表和双链表的视频,但我还没有看到这种实现。 What's the logic behind, for example:
trailer = new Node<>(null, header, null)
?背后的逻辑是什么,例如:
trailer = new Node<>(null, header, null)
?
You have Probably some DoubleLinkedList like:你可能有一些 DoubleLinkedList 像:
/**
* A double linked list.
*
*/
public class DoubleLinkedList<E> {
private final Node<E> header; // header sentinel
private final Node<E> trailer; // trailer sentinel
private int size = 0; // number of elements in the list
private int modCount = 0; // number of modifications to the list (adds or removes)
public DoubleLinkedList() {
this.header = new Node<>(
// The successor of the header is the trailer.
// It will be set with: header.setNext(trailer);
null,
// The predecessor of the header is always null,
// because there there is no node before the first
null,
// The payload of the node is null.
// I guess it is just a part of the example.
null
);
this.trailer = new Node<>(
// The successor of the trailer is always null,
// because there there is no node after the last
null,
// The predecessor of the trailer is the header
// at construction of this object
header,
// The payload of the node is null.
// I guess it is just a part of the example.
null
);
// Now is the successor of the header set to the trailer.
header.setNext(trailer);
}
// Some list methods like add, remove, get, ...
/**
* The nodes of the List
*
* @param <T> The type of the stored objects in the list.
*/
static class Node<T> {
/**
* The predecessor of this node.
*/
private Node<T> predecessor;
/**
* The successor of this node.
*/
private Node<T> successor;
/**
* The payload
*/
private final T payload;
public Node(final Node<T> successor, final Node<T> predecessor, final T payload) {
this.predecessor = successor;
this.successor = successor;
this.payload = payload;
}
// Getter and Setter:
private Node<T> getPredecessor() {
return this.predecessor;
}
private void setNext(final Node<T> next) {
this.predecessor = next;
}
private Node<T> getSuccessor() {
return this.successor;
}
private void setPrevious(final Node<T> previous) {
this.successor = previous;
}
private T getPayload() {
return this.payload;
}
}
}
This is architectural not very beautiful, but I think this explanation matches your case.这是建筑不是很漂亮,但我认为这个解释符合你的情况。
Given a list (of any kind), you need to know at least how to get to the first element, and how to tell when you've seen the last element.给定一个列表(任何类型的),您至少需要知道如何到达第一个元素,以及如何判断何时看到了最后一个元素。
There are a few ways to arrange for these requirements to be satisfied.有几种方法可以满足这些要求。
For a linked list, to know where the list starts, you might have a simple references to the first node, or you might have a full 'dummy' node that always exists.对于链表,要知道列表从哪里开始,您可能有对第一个节点的简单引用,或者您可能有一个始终存在的完整“虚拟”节点。
To know where the list ends, you might have a null 'next' reference, or you might have a full 'dummy' node that always exists.要知道列表在哪里结束,您可能有一个空的“下一个”引用,或者您可能有一个始终存在的完整“虚拟”节点。
The dummy-node approach can often result in cleaner code, because then all actual nodes will always have a 'previous' node, and all actual nodes will always have a 'next' node.虚拟节点方法通常可以产生更清晰的代码,因为所有实际节点将始终具有“上一个”节点,而所有实际节点将始终具有“下一个”节点。
That seems to be the approach being taken in your code extract.这似乎是您的代码提取中采用的方法。
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