Question

I am reading the source code of Java LinkedList, and note that the constructor of LinkedList is like this:

public LinkedList() {
    header.next = header.previous = header;
}

How much space will be allocated to this initialization, the header seems to create infinite recursion by pointing to itself.

Answer 1

It allocates a single node in the initialization of the header instance variable:

private transient Entry<E> header = new Entry<E>(null, null, null);

The code in the constructor to which you refer allocates no memory; it merely sets up the pointers to an initial state. There is no “infinite recursion”, because internal traversal caters for this situation.