Apache Commons Collections - Merging Sorted Data

Merging two sorted lists

Syntax

collate() method of CollectionUtils can be used to merge two already sorted lists.

List<String> mergedList = CollectionUtils.collate(sortedList1, sortedList2);

Declaration

Following is the declaration for

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

public static <O extends Comparable<? super O>> List<O>
   collate(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

A new sorted List, containing the elements of Collection a and b.

Exception

• NullPointerException − If either collection is null.

Example - Merging two sorted Lists

The following example shows the usage of collate() method. We'll merge two sorted lists and then print the merged and sorted list.

CommonCollectionsTester.java

package com.tutorialspoint;

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

public class CommonCollectionsTester { 
   public static void main(String[] args) {
      List<String> sortedList1 = Arrays.asList("A","C","E");
      List<String> sortedList2 = Arrays.asList("B","D","F");
      List<String> mergedList = CollectionUtils.collate(sortedList1, sortedList2);
      System.out.println(mergedList);
   }
}

Output

The output is as follows −

[A, B, C, D, E, F]