Union of Two Arrays in Java

Learn to find the union between two arrays in Java using HashSet class. In set theory, the union (denoted by U) of a collection of sets is the set of all elements in the collection.

For example, the union of two sets A and B is the set of all the elements which are either in A, or in B, or in both A and B.

To get the union of two arrays, follow these steps:

1. Push first array in a HashSet instance.
2. Use addAll() method to add the elements of the second array into set.
3. Similarly, add all the elements of more arrays in the set, if any.

1. Union between two integer arrays

Java program to get the union between two integer arrays and print the output.

import java.util.Arrays;
import java.util.HashSet;

public class Main 
{
  public static void main(String[] args) 
  {
    Integer[] firstArray = {0,2,4,6,8};
      Integer[] secondArray = {1,3,5,7,9};
      
      HashSet<Integer> set = new HashSet<>(); 
      
      set.addAll(Arrays.asList(firstArray));
      
      set.addAll(Arrays.asList(secondArray));
      
      System.out.println(set);
    
    //convert to array
      Integer[] union = {};
    union = set.toArray(union);
    
    System.out.println(Arrays.toString(union));
  }
}

Program output.

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

2. Union between two string arrays

Java program to get the union between two string arrays and print the output.

import java.util.Arrays;
import java.util.HashSet;

public class Main 
{
  public static void main(String[] args) 
  {
    String[] firstArray = {"A", "B", "C", "D"};
    String[] secondArray = {"D", "A", "E", "F"};
    
    HashSet<String> set = new HashSet<>(); 
    
    set.addAll(Arrays.asList(firstArray));
    
    set.addAll(Arrays.asList(secondArray));
    
    System.out.println(set);
    
    //convert to array
    String[] union = {};
    union = set.toArray(union);
    
    System.out.println(Arrays.toString(union));
  }
}

Program output.

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

Happy Learning !!

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