Make my own FIFO Queue class for my own class object to fill it?

Question

Hello. I am trying to make a FIFO Queue that is filled with my own class object.
I found this example but if I replace < E > with < PCB > it does not work:

import java.util.LinkedList;


public class SimpleQueue<E> {

private LinkedList<E> list = new LinkedList<E>();


 public void put(E o) {
    list.addLast(o);
     }


  public E get() {
     if (list.isEmpty()) {
          return null;
      }
   return list.removeFirst();
   }


   public Object[] getAll() {
     Object[] res = new Object[list.size()];
    for (int i = 0; i < res.length; i++) {
      res[i] = list.get(i);
      }
   list.clear();
    return res;
 }



    public E peek() {
      return list.getFirst();
      }


  public boolean isEmpty() {
     return list.isEmpty();
    }


  public int size() {
    return list.size();
    }
  }

Answer 1

E is a type parameter. In simple terms, you can consider it as a 'template' which can be used to create a queue that can hold instances of one particular class.

You can create a queue of your PCB objects as follows:

SimpleQueue<PCB> queue = new SimpleQueue<PCB>();

Java Generics FAQs is a good resource if you want to learn more about Java generics.

Answer 2

Ignoring your immediate issue, are you aware that Java has a generic Queue already ? See the implementations linked from this interface specification.

Answer 3

The sun's generic tutorial says following:

We recommend that you use pithy (single character if possible) yet evocative names for formal type parameters. It’s best to avoid lower 3 case characters in those names, making it easy to distinguish formal type parameters from ordinary classes and interfaces. Many container types use E, for element, as in the examples above.

So, it can't be the problem that you changed it to PCB.

But if PCB is the only class of which you want to store objects, you don't have to create a generic class. Just remove <PCB> from your class definition line and replace all E's with PCB:

public class SimpleQueue
{
    LinkedList<PCB> list = new LinkedList<PCB>();

    ....

    public PCB peek()
    {
        return list.getFist();
    }
}