how to add a singleton hashset in java

To add a singleton set (a set with a single element) to a java.util.HashSet in Java, you can use the add method of the HashSet class. This method adds an element to the set if it is not already present.

Here's an example of how you could create a singleton set and add it to a HashSet:

import java.util.HashSet;
import java.util.Set;

public class Main {
  public static void main(String[] args) {
    Set<String> set = new HashSet<>();
    set.add("Apple"); // Add the element to the set

    Set<String> singletonSet = Set.of("Banana"); // Create a singleton set

    set.addAll(singletonSet); // Add the singleton set to the original set

    System.out.println(set); // [Apple, Banana]
  }
}

In this example, the Set.of method is used to create a singleton set that contains the element "Banana". The addAll method is then used to add the singleton set to the set set.

Keep in mind that the HashSet class does not maintain the order of the elements, so the order in which the elements are added to the set may not be the same as the order in which they are returned by the toString method or iterated over using an iterator.

If you need to maintain the order of the elements in the set, you can use a different implementation of the Set interface, such as the LinkedHashSet class, which maintains the insertion order of the elements.