Removing dups from list

Question

Hello
i am removing dups from a list by overwriting the equals method of the class. The equals method is checking for only one attribute...but i want to have another list with different elements from the list (another attribute)
class C has two main attributes, Color and Size. I want to have a list with different colors and another list with different sizes.
class C equals method:
public boolean equals(Object obj) {
     C drt = (C) obj;
     boolean bRet;
     if (drt.getColor().equals(this.getColor()) {
          bRet = true;
     else {
          bRet = false;
     return bRet;
}adding to list A
ListIterator li  = B.listIterator();
while (li.hasNext())
C celement = (C) li.next();
if (!A.equals(celement))
   A.add(celement);
}at this point list A consists of different (by color) celements. But what if i want to have another list to have different (by size) celements...?

Answer 1

The obvious way of getting a collection of distinct things is to use a Set. However you can't have multiple "equals()" methods. There is no inbuilt "Equivalator" analogous to a Comparator.
At the moment you are comparing a list with an element which can't be good.
One way or another you have to compare each thing with the list so far to see if it should be added. Maybe something like:import java.util.ArrayList;
import java.util.List;
public class Thing {
    private String color;
    private String size;
    public Thing(String color, String size) {
        this.color = color;
        this.size = size;
    public String getColor() {
        return color;
    public String getSize() {
        return size;
    public String toString() {
        return "[" + color + "," + size + "]";
    public static void main(String[] args) {
        List<Thing> theThings = new ArrayList<Thing>();
        theThings.add(new Thing("a", "1"));
        theThings.add(new Thing("b", "1"));
        theThings.add(new Thing("a", "2"));
        theThings.add(new Thing("b", "2"));
        theThings.add(new Thing("c", "3"));
        theThings.add(new Thing("d", "1"));
        List<Thing> colorList = new ArrayList<Thing>();
        List<Thing> sizeList = new ArrayList<Thing>();
        for(Thing thing :theThings) {
                // look for a color match
            boolean found = false;
            for(Thing test :colorList) {
                if(test.getColor().equals(thing.getColor())) {
                    found = true;
                    break;
            if(!found) colorList.add(thing);
                // look for a size match
            found = false;
            for(Thing test :sizeList) {
                if(test.getSize().equals(thing.getSize())) {
                    found = true;
                    break;
            if(!found) sizeList.add(thing);
        System.out.println("Color list: " + colorList);
        System.out.println("Size list: " + sizeList);
}