Having trouble removing duplicates from list

Question

Hello
I am strugling with this
I have a ArrayList as i am adding stuff in it i want to make sure i am adding just the Unique stuff. I am adding objects of class paper in the list. paper class has an attribute called color. so i have overwritten the equals method of paper class like this
public boolean equals(Object other)
if (!(other instanceof paper)
    return false;
paper detTo = (paper) other;
          return detTo.getColor().equalsIgnoreCase(this.getColor());
}while I am adding stuff to the list i am doing this
List onlyColor = new ArrayList();
while (li.hasNext())
paper p1 = (paper) li.next();
if (!onlyColor.equals(p1)) //only add when equals returns false?
   onlyColor.add(p1);
   System.out.println("Adding: " + p1.getColor());
}but it is still adding duplicate stuff in the list (onlyColor). what am i doing wrong!? i heard that i should overwrite the hashcode as well...but how can i do it..can anyone help? Also does it matter that class paper is extending another class called utilities. and getColor() attribute is actually in the utilities class..?
Thanks! please help me solve this :(
Message was edited by:
Omnipresent
also, if i chance the equals method to always return true by default
public boolean equals(Object other)
if (!(other instanceof paper)
    return false;
paper detTo = (paper) other;
          return true;
}and then change
if (!onlyColor.equals(p1)) to
if (onlyColor.equals(p1)) nothing is being added to the list!! i am suspicious if my overwritten equals method is even called!!?!?

Answer 1

i am planning to get this book
http://www.amazon.com/Certified-Programmer-310-055-Certification-Guides/dp/0072253606
have u come across this one before?
if i go thru this..do u you think i'll be uptodate
with java5?That's what the goal of that book: getting you ready for a Java 5 certification. Personally I'd start with a decent Java book like this one: http://www.sun.com/books/catalog/gosling_JPL4.xml
and perhaps a data structures and algorithms book.
After that, buy yourself a certification book to see what's important to know when taking an exam.
A certification book will not make you a good programmer. Don't get me wrong: a decent Java book won't make you a good programmer over night either, but it's (IMO) a better basis to learn the language than a certification book.