Apache Commons Collections - Inclusion

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

Checking sublist

isSubCollection() method of CollectionUtils can be used to check if a collection contains the given collection or not.

Declaration

Following is the declaration for

org.apache.commons.collections4.CollectionUtils.isSubCollection()method −

public static boolean isSubCollection(Collection<?> a,
   Collection<?> b)

Parameters

• a − The first (sub) collection, must not be null.
• b − The second (super) collection, must not be null.

Return Value

True if and only if a is a sub-collection of b.

Example

The following example shows the usage of org.apache.commons.collections4.CollectionUtils.isSubCollection() method. We'll check a list is part of another list or not.

import java.util.Arrays;
import java.util.List;

import org.apache.commons.collections4.CollectionUtils;

public class CollectionUtilsTester {
   public static void main(String[] args) {
      //checking inclusion
      List<String> list1 = Arrays.asList("A","A","A","C","B","B");
      List<String> list2 = Arrays.asList("A","A","B","B");

      System.out.println("List 1: " + list1);
      System.out.println("List 2: " + list2);
      System.out.println("Is List 2 contained in List 1: " 
         + CollectionUtils.isSubCollection(list2, list1));
   }
}

Output

It will print the following result.

List 1: [A, A, A, C, B, B]
List 2: [A, A, B, B]
Is List 2 contained in List 1: true