Java链表实现中的入队操作中分配如何工作

Question

I recently tried to implement a queue with linked list in Java. enqueue , The function to add items to the queue is as follows.

void enqueue(int key) 
    { 

        // Create a new LL node 
        Node temp = new Node(); 

        // If queue is empty, then new node is front and rear both 
        if (this.rear == null) {
            temp.setData(key); 
            this.front = this.rear = temp; 
            return; 
        } 
        temp.setData(key);
        // Add the new node at the end of queue and change rear 
        this.rear.setLink(temp); 
        this.rear = temp; 
    }

class Node{

    private int data;
    private Node link;

    public int getData(){
        return this.data;
    }

    public void setData(int data){
        this.data = data;
    }

    public Node getLink(){
        return this.link;
    }

    public void setLink(Node link){
        this.link = link;
    }

    public Node(){
    }
}

This is working as expected, but the thing that I cannot understand is the last two lines of this function.first we set the link of current rear to the new node, then immediately rear is assigned the new node. What happened to the previous value stored in rear ?

Answer 1

rear is just a reference which points to the last element inserted into the Queue. Lets say your current queue has the following elements 1 -> 2 -> 3(rear) . The rear is now pointing to 3. Now let's say you call enqueue(4). The current rear's link(next) pointer should point to the new node. The line this.rear.setLink(temp) is doing exactly that. The current queue's contents will be 1 -> 2 -> 3(rear) -> 4 . We need to update the new rear . this.rear = temp is doing exactly that. Eventually the queue's contents will be 1 -> 2 -> 3 -> 4(rear)