Consider the following partially complete class:

public class TestClass implements Comparable { private String lastName; private String firstName public TestClass( String lastName, String firstName ) { this.lastName = lastName; this.firstName = firstName; } public String getLastName() { return this.lastName; } public String getFirstName() { return this.firstName; } public int compareTo( Object obj ) { // complete the code here } }

Using the Comparable interface, write a compareTo( ) method that returns -1 if the private instance variable firstName occurs lexicographically before obj, 0 if the private instance variable firstName and obj are lexicographically the same, or 1 if the private instance variable firstName occurs lexicographically after obj. Use a getter method any time you need to use a private instance variable.