Studying: Day Two

When we last left off I was working on stacks. I'm gonna implement it with a linked list by deriving off my linked list class. On the way I am also going to change the class to use generics. It turns out it's super easy to create generic classes in Java:

class LinkedListNode 
{
    public LinkedListNode(T newData)
    {
        data = newData;
    }

    LinkedListNode next = null;
    T data; 
};

public class LinkedList  {
// etc
};

I'm told that generics in Java are sorta bad because they use type erasure. This is when the compiler "erases" the types of generic classes, so it's compatible with any old non-generic classes. This means if a class has type T, you cannot reference T anywhere in your code, like you could with C++ templates. In fact, the other day one of my coworkers was complaining that they have to duplicate code that creates a new class of a generic type just for this reason.

public class Stack  extends LinkedList 
{
    public Stack()
    {
        super();
    }

    public void push(LinkedListNode node)
    {
        node.next = _root;
        _root = node;        
    }

    public LinkedListNode pop()
    {
        LinkedListNode ret = _root;
        _root = _root.next;

        return ret;
    }
} 

and then a queue is trivial:

public class Queue  extends LinkedList
{
    public void enqueue (LinkedListNode node)
    {
        insert(node);
    }

    public LinkedListNode dequeue ()
    {
        LinkedListNode ret = _root;
        _root = _root.next;
        return ret;
    }
}