The Collections Framework - Beginning Java - page 671

TRY IT OUT: Using a HashMap Map
You need to improve your old Person class to make Person objects usable as keys in the map that you
use — to store the phone book entries. You must add an equals() method to do this, and you override
the default hashCode() method just to show how this can work. The extended version of the class is as
follows:
import java.io.*;
public class Person implements Comparable<Person>, Serializable {
@Override
public boolean equals(Object person) {
return compareTo((Person)person) == 0;
}
@Override
public int hashCode() {
return 7*firstName.hashCode()+13*surname.hashCode();
}
// The rest of the class as before...
private static final long serialVersionUID = 1001L;
}
Directory "TryPhoneBook 1"
You've added to the previous version of the class two methods that override the equals() and
hashCode() methods inherited from Object and defined serialVersionUID for the class. Because the
String class defines a good hashCode() method, you can easily produce a hash code for a Person ob-
ject from the data members. To implement the equals() method you just call the compareTo() method
that you implemented for the Comparable<> interface. You have also made the class serializable just in
case it comes in useful at some point.
There's another thing you can do that is definitely useful. You can add a static method to the Person
class that reads data for a Person object from the keyboard:
import java.io.*;
public class Person implements Comparable<Person>, Serializable {
// Read a person from the keyboard
public static Person readPerson() {
String firstName = null;
String surname = null;