How is LinkedList added?

Problem description ：

1,LinkedList When you do the initialization

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

2,add Method

    /** * 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;
    }

3, Go to linkLast(e); Method down tracking , The current is the core method of adding

    /** * Links e as last element. */
    void linkLast(E e) {
    
    	/* *  The first time I added it ,last  Is a currently defined Node<E> Object variables  * //transient Node<E> last; */
        final Node<E> l = last;
        /* *  Before we create a new Node When the object ,Node In the construction method  *  The first value is ：prev  Point to the previous object  *  Second value ：item  Currently added element  *  Third values ：next  Point to the next object  */
        final Node<E> newNode = new Node<>(l, e, null);
        //  After creation   Assign to current  last
        last = newNode;
        //  Judge l Is it equal to null, so l Namely last The assignment of , In the first addition 
        // last Namely null  therefore l The variable of is null
        if (l == null) //  Meet the conditions 
            first = newNode;//  Assign a value to first
        else
            l.next = newNode;
        size++;//  Index plus 
        modCount++; //  The number of modifications is increased 
    }

4, This is the result of the first addition

5, When making the second addition

    /** * Links e as last element. */
    void linkLast(E e) {
    
    	/* *  The second time you add ,last  It was the last one before Node object  */
        final Node<E> l = last;
        /* *  Before we create a new Node When the object ,Node In the construction method  *  The first value is ：prev  Point to the previous object , So , When we create the second object  *  Now this prev Will point to the previous  *  Second value ：item  Currently added element  *  Third values ：next  Point to the next object  */
        final Node<E> newNode = new Node<>(l, e, null);
        //  After creation   Assign to current  last  the last one 
        last = newNode;
        //  Judge l Is it equal to null, here l It's the last one Node object 
        // l It's not equal to null
        if (l == null) //  Not meeting the conditions 
            first = newNode;
        else
        	//  Let the last Node Of next Point to the newly created node 
            l.next = newNode;
        size++;//  Index plus 
        modCount++; //  The number of modifications is increased 
    }

6, The schematic diagram added for the second time

7, From this, we can infer , Every time you add a new node , Nodes are appended later , New node's prev Will point to the previous node , The previous node will point to the current new node

8,Node The node is the current static inner class

    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;
        }
    }