A HashSet stores each value once. add returns false when the value is already present. There is no index. Use a set when you care about membership, such as skills a learner already has.
contains is the test you want. Loop with for-each when you need to print the values. The order is not guaranteed.
Example
The second add of Java does not create a second item. size stays 1, and contains is true.
import java.util.HashSet;
public class Skills {
public static void main(String[] args) {
HashSet<String> skills = new HashSet<>();
skills.add("Java");
skills.add("Java");
System.out.println(skills.size());
System.out.println(skills.contains("Java"));
}
}String, Integer, and other well-built types work as set items because equals and hashCode agree. If you put your own class in a HashSet, those two methods must agree too.
