Union and Intersection of two Set in Java - Google Guava Example

Google
Guava is an open source library which provides lots of useful utility to Java
programmer,  one of them is easy way to find
intersection and union of two Set in Java. You might have used Google
Guava for other functionality e.g. for overriding
toString in easy way or Immutable Collection provided by Guava library.
Along with Apache commons and Spring, Google Guava is a library you definitely want
to include in your Project. Guava provides couple of static
method to operate on Set
in Java on package com.google.common.collect.Sets. There are
two methods called intersection() and union() which
provides intersection and union of two
Sets in Java. In this example we have used HashSet
as Set implementation but it will work with any Set implementation e.g. TreeSet
or LinkedHashSet.

How to find Intersection and Union of two
Set in Java

Here is complete code example of How
to calculate union and intersection of two Set in Java. It use's static
method Sets.intersection() and Sets.union() to find
intersection and union of two Sets in Java.

package test;



import com.google.common.collect.Sets;

import java.util.HashSet;

import java.util.Set;



/**

 *

 * Java program to demonstrate How to calculate Intersection and Union of
two

 * Set using Google's Guava library example.

 *

 * @author http://javarevisited.blogspot.com.au

 */

public class
SetIntersectionExample {



 

    public static void
main(String args[]) {

 

        // Set which stores
some Singer

        Set<String> singers = new
HashSet<String>();

        singers.add("Amitabh
Bacchan");

        singers.add("Shan");

        singers.add("Medona");

     

        // Another Set which
stores Actors

        Set<String> actors = new
HashSet<String>();

        actors.add("Amitabh
Bacchan");

        actors.add("tom cruise");

        actors.add("SRK");

     

        // Calculating
Intersection of two Set in Java

        Set<String> intersection = Sets.intersection(actors, singers);

        System.out.printf("Intersection of two Set %s and %s in Java is %s
%n",

                singers.toString(),
actors.toString(),
intersection.toString());

        System.err.println("Number of elements common in two Set : "

                           + intersection.size());

     

        // Calculating Union
of two Set in Java

        Set<String> union = Sets.union(actors, singers);

        System.out.printf("Union of two Set %s and %s in Java is %s %n",

                singers.toString(),
actors.toString(),
union.toString());

        System.out.println("total number of element in union of two Set is :
"

                            + union.size());

    }

     

}



Output:

Intersection of two Set [Medona,
Shan, Amitabh Bacchan] and [SRK, tom cruise, Amitabh Bacchan] in Java is [Amitabh
Bacchan]



Number of elements common in two Set : 1

Union of two Set [Medona, Shan,
Amitabh Bacchan] and [SRK, tom cruise, Amitabh Bacchan]
in Java is [SRK, tom cruise, Amitabh
Bacchan, Medona, Shan]



total number of element in union of two Set is : 5

That's all on How to find Union and Intersection of two Set in Java.
It's very simple if you are using right open source library e.g. Google's Guava
Collection. If you don't like to use open source library, you can write your
own method to do the same thing, But as Joshua Bloch suggested in its popular
book Effective Java, Use library method as much as possible. That's encourages
me to explore more on Apache commons, Google Guava and Spring framework API
more and more and I did find couple of gems like calculating
time difference with Stopwatch in Spring framework which helps a lot.

Source:http://javarevisited.blogspot.com/2012/12/union-and-intersection-of-two-set-in-java-guava-example.html