To modify an element in a set, you should remove it, modify it, and then re-add it.
import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;
public class MainClass {
public static void main(String[] a) {
String elements[] = { "A", "B", "C", "D", "E" };
Set set = new HashSet(Arrays.asList(elements));
set.add("Z");
System.out.println(set);
}
}
[Z, D, A, C, B, E]