Sets union() function | Guava | Java

Guava’s Sets.union() returns an unmodifiable view of the union of two sets. The returned set contains all elements that are contained in either backing set. Iterating over the returned set iterates first over all the elements of set1, then over each element of set2, in order, that is not contained in set1.

Syntax:

public static <E> 
  Sets.SetView<E> 
    union(Set<? extends E> set1, 
          Set<? extends E> set2)

Return Value: This method returns an unmodifiable view of the union of two sets.

Example 1:

// Java code to show implementation
// of Guava's Sets.union() method

import com.google.common.collect.Sets;
import java.util.Set;

class GFG {

    // Driver's code
    public static void main(String[] args)
    {
        // Creating first set
        Set<Integer>
            set1 = Sets.newHashSet(1, 2, 3, 4, 5);

        // Creating second set
        Set<Integer>
            set2 = Sets.newHashSet(3, 5, 7, 9);

        // Using Guava's Sets.union() method
        Set<Integer>
            answer = Sets.union(set1, set2);

        // Displaying the union of set set1 and set2
        System.out.println("Set 1: "
                           + set1);
        System.out.println("Set 2: "
                           + set2);
        System.out.println("Set 1 union Set 2: "
                           + answer);
    }
}

Output:

Set 1: [1, 2, 3, 4, 5]
Set 2: [9, 3, 5, 7]
Set 1 union Set 2: [1, 2, 3, 4, 5, 9, 7]

Example 2:

// Java code to show implementation
// of Guava's Sets.union() method

import com.google.common.collect.Sets;
import java.util.Set;

class GFG {

    // Driver's code
    public static void main(String[] args)
    {
        // Creating first set
        Set<String>
            set1 = Sets.newHashSet("G", "e", "e", "k", "s");

        // Creating second set
        Set<String>
            set2 = Sets.newHashSet("g", "f", "G", "e");

        // Using Guava's Sets.union() method
        Set<String>
            answer = Sets.union(set1, set2);

        // Displaying the union of set set1 and set2
        System.out.println("Set 1: "
                           + set1);
        System.out.println("Set 2: "
                           + set2);
        System.out.println("Set 1 union Set 2: "
                           + answer);
    }
}

Output:

Set 1: [k, s, e, G]
Set 2: [e, f, g, G]
Set 1 union Set 2: [k, s, e, G, f, g]