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Find Union of Two Collections in Java

I explained in this post how to find the intersection of two collections in Java. This post will explain how to find the union of two collections. A union means finding all unique values from the two lists combined.

import java.util.*;
 
public static Collection Union(Collection coll1, Collection coll2)
{
    Set union = new HashSet(coll1);
    union.addAll(new HashSet(coll2));
    return new ArrayList(union);
}
 
Set set1 = new HashSet();
set1.add("abc");
set1.add("def");
 
Set set2 = new HashSet();
set2.add("def");
set2.add("ghi");
 
for (Object item : Intersect(set1, set2))
    System.out.println(item);

This would output:

abc

def

ghi

This entry was posted on Saturday, October 25th, 2008 at 9:55 pm and is filed under Tip. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

One Response to “Find Union of Two Collections in Java”

  1. You have a nifty blog here. I always find blogs like this really interesting because I come across solutions to things I had given up on before or problems I wouldn’t have foreseen. You’ve got yourself at least one regular reader.

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