Generics/Templates

• Based on GJ and Pizza

• Probably a good idea.

• An example adapted from the GJ Tutorial by Gilad Bracha, et al:

  interface Collection<A> {
    public void add(A x);
    public Iterator<A> iterator();
  }
  
  interface Iterator<> {
    public A next();
    public boolean hasNext();
  }
  
  class LinkedList<A> implements Collection<A> {
  
    protected class Node {
      A elt;
      Node next = null;
      Node (A elt) { this.elt=elt; }
    }
    
    protected Node head = null
    protected Node tail = null;
    
    public LinkedList () {}
    
    public void add (A elt) {
      if (head==null) { head=new Node(elt); tail=head; }
      else { tail.next=new Node(elt); tail=tail.next; }
    }
    
    public Iterator<A> iterator () {
      return new Iterator<A> () {
        protected Node ptr=head;
        public boolean hasNext () { return ptr!=null; }
        public A next () {
          if (ptr!=null) {
            A elt=ptr.elt; ptr=ptr.next; return elt;
          } 
          else {
            throw new NoSuchElementException ();
          }
        }
      };
   }
  

• Undocumented support for this in Java 1.3!

• All the tricks are in the compiler; doesn't change the byte code at all.

• May be documented for Java 1.4