Java - Errores en Codigo Java Ayudaaa

interface ICola{

	public boolean llena();

	public boolean vacia();

	public void insertar (Object elem);

	public Object eliminar();

}

class Cola implements ICola {

	private Object[] cola;

	private int frente = -1;

	private int fin = -1;

	private int size;

	public Cola(int s){

  	      size = s-1;

             cola = new Object[s];

       }

       public boolean vacia(){

           return (frente == -1);

       }

       public boolean llena(){

           return ( fin == size );

       }

       public void insertar( Object elem) {

	     if ( frente == -1 )

		  frente ++;

 	    else

                if ( fin == size)

                      ERROR Cola Llena!

           fin ++;

           cola[fin]=elem;

         }

    }

    public Object eliminar(){

         …

    }

}

class Cola<T> implements ICola<T> {

	private T[] cola;

	private int frente = -1;

	private int fin = -1;

	private int size;

         public Cola(int s){

  	     size = s-1;

              cola = new T[s];

         }

         public boolean vacia(){

             return (frente == -1);

         }

         public boolean llena(){

              return ( fin == size );

         }

         public void insertar( T elem) {

           ...

	 }

          public T eliminar(){

         …

          }

}

public interface ICola{

	public boolean llena();

	public boolean vacia();

	public void insertar (Object elem);

	public Object eliminar();

}

public class IColaImpl implements ICola {

	@Override

	public boolean llena() {

		// TODO Auto-generated method stub

		return false;

	}

	@Override

	public boolean vacia() {

		// TODO Auto-generated method stub

		return false;

	}

	@Override

	public void insertar(Object elem) {

		// TODO Auto-generated method stub

	}

	@Override

	public Object eliminar() {

		// TODO Auto-generated method stub

		return null;

	}

}