Testing the TreeSet Class in Java

Problem:

Write a java problem that tests the treeset class.

Output:

[GB, IN, NG, PH, PK, US, ZA]
[GB, IN, KE, NG, PH, PK, US, ZA]
[GB, IN] [KE, NG, PH, PK] [US, ZA]
engl.first(): GB
engl.last(): ZA
engl.lower("KE"): IN
engl.higher("KE"): NG

Solution:

public class TestTreeSet {
public static void main(String[] args) {
NavigableSet<String> engl = new TreeSet<String>();
Collections.addAll(engl, "IN", "US", "PK", "NG", "PH", "GB", "ZA");
System.out.println(engl);
engl.add("KE");
System.out.println(engl);
SortedSet<String> head = engl.headSet("KE");
SortedSet<String> mid = engl.subSet("KE", "US");
SortedSet<String> tail = engl.tailSet("US");
System.out.printf("%s %s %s%n", head, mid, tail);
System.out.printf("engl.first(): %s%n", engl.first());
System.out.printf("engl.last(): %s%n", engl.last());
}
}