Re: Generics, extending LinkedList<T>, and unchecked casts

"Daniel Dyer" <"You don't need it">
Wed, 27 Dec 2006 23:50:40 -0000
On Wed, 27 Dec 2006 23:29:29 -0000, Mark Maloof <maloof@cs.georgetown.ed=
u> =


I need an ordered sequence, so I extended LinkedList<T>. Since I'm
implementing an ordered collection, its elements must implement
Comparable<T>. I came up with the following implementation, which
seems to work, but I cannot figure out how to avoid the unchecked cast=

at the end of the insert method:

public class OrderedLinkedList<E> extends LinkedList<E> {

  public void insert( Comparable<E> element ) {
    int i = 0;
    while ( i < size() && element.compareTo( this.get( i ) ) >= 0 ) =


    } // while
    // add( i, element ); // compiler error
    add( i, (E) element ); // unchecked cast
  } // OrderedLinkedList::add

  public static void main ( String args[] ) {
    OrderedLinkedList<String> oll = new OrderedLinkedList<String>();=

    System.out.println( oll );
  } // OrderedLinkedList::main

} // OrderedLinkedList class

A class that implements Comparable<E> is not itself necessarily assignab=
le =

to references of type E, it just means it can be compared with instances=

of E.

If you don't need duplicates you could just use a SortedSet. If you do =

need to deal with duplicates, you could try this:

    public class SortedList<E extends Comparable<E>> extends LinkedList<E>

This means you can only use the list with types that are comparable to =


The other option you have is to follow the TreeSet way of doing things a=
nd =

drop the requirement for Comparable and allow a Comparator to be specifi=

Also, OrderedList is a bad name, lists are, by definition, ordered. =

SortedList might be a better name, at least it will be consistent with =

java.util.SortedSet then.


-- =

Daniel Dyer - Evolutionary Algorithm Framework for J=

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