Sorting collection of String and StringBuffer in Java

// Java program to sort String objects using TreeSet
import java.util.Set;
import java.util.TreeSet;

public class Test {
    public static void main(String[] args)
    {
        Set<String> str = new TreeSet<String>();
        str.add("Sohan");
        str.add("Raja");
        str.add("Harish");
        str.add("Ram");
        System.out.println(str);
    }
}

// Java program to demonstrate that simple sorting
// StringBuffer objects does work.
import java.util.Set;
import java.util.TreeSet;

public class Test {

    public static void main(String[] args)
    {
        Set<StringBuffer> str = new TreeSet<>();
        str.add(new StringBuffer("Sohan"));
        str.add(new StringBuffer("Raja"));
        str.add(new StringBuffer("Harish"));
        str.add(new StringBuffer("Ram"));
        System.out.println(str);
    }
}

public final class String
    extends Object
        implements Serializable,
    Comparable, CharSequence

public final class StringBuffer
    extends Object
        implements Serializable,
    CharSequence

public final class StringBuilder
    extends Object
        implements Serializable,
    CharSequence

// Java program to demonstrate sorting
// of StringBuffer objects using Comparator
// interface.
import java.util.Comparator;
import java.util.Set;
import java.util.TreeSet;

public class Test implements Comparator<StringBuffer> {
    @Override public int compare(StringBuffer s1, StringBuffer s2)
    {
        return s1.toString().compareTo(s2.toString());
    }

    public static void main(String[] args)
    {
        Set<StringBuffer> str = new TreeSet<>(new Test());
        str.add(new StringBuffer("Sohan"));
        str.add(new StringBuffer("Raja"));
        str.add(new StringBuffer("Harish"));
        str.add(new StringBuffer("Ram"));
        System.out.println(str);
    }
}