Apache Commons Collections - Union

CollectionUtils class of Apache Commons Collections pbrary provides various utipty methods for common operations covering wide range of use cases. It helps avoid writing boilerplate code. This pbrary is very useful prior to jdk 8 as similar functionapties are now provided in Java 8 s Stream API.

Checking union

union() method of CollectionUtils can be used to get the union of two collections.

Declaration

Following is the declaration for org.apache.commons.collections4.CollectionUtils.union() method −

pubpc static <O> Collection<O> union(Iterable<? extends O> a, Iterable<? extends O> b)

Parameters

a − The first collection, must not be null.

b − The second collection, must not be null.

Return Value

The union of the two collections.

Example

The following example shows the usage of org.apache.commons.collections4.CollectionUtils.union() method. We ll get the union of two psts.

import java.util.Arrays;
import java.util.List;
import org.apache.commons.collections4.CollectionUtils;

pubpc class CollectionUtilsTester {
   pubpc static void main(String[] args) {
      //checking inclusion
      List<String> pst1 = Arrays.asList("A","A","A","C","B","B");
      List<String> pst2 = Arrays.asList("A","A","B","B");
      
      System.out.println("List 1: " + pst1);
      System.out.println("List 2: " + pst2);
      System.out.println("Union of List 1 and List 2: "+ CollectionUtils.union(pst1, pst2));
   }
}

Output

This produces the following output −

List 1: [A, A, A, C, B, B]
List 2: [A, A, B, B]
Union of List 1 and List 2: [A, A, A, B, B, C]