Java Reference
In-Depth Information
238
Enter the number:
6778
Enter 1 to enter a new phone book entry
Enter 2 to find the number for a name
Enter 9 to quit.
2
Enter first name:
Slim
Enter surname:
"Pickens"
The number for Slim Pickens is 914 238 6778
Enter 1 to enter a new phone book entry
Enter 2 to find the number for a name
Enter 9 to quit.
9
Ending program.
Of course, you can try it with several entries if you have the stamina.
How It Works
The
main()
method runs an ongoing loop that will continue until a
9
is entered. When a
1
is entered,
the
addEntry()
method for the
PhoneBook
object is called with the expression
BookEntry.readEntry()
as the argument. The
static
method
readEntry()
calls the
static
methods in the
Person
class and the
PhoneNumber
class to read from the keyboard and create objects
of these classes. The
readEntry()
method then passes these objects to the constructor for the
BookEntry
class, and the object that is created is returned. This object will be added to the
HashMap
member of the
PhoneBook
object.
If a
2
is entered, the
getEntry()
method is called. The argument expression calls the
readPerson()
member of the
Person
class to obtain the
Person
object corresponding to the name
entered from the keyboard. This object is then used to retrieve an entry from the map in the
PhoneBook
object. Of course, if there is no such entry
null
will be returned, so we have to check for
it and act accordingly.
Storing a Map in a File
This phone book is not particularly useful. The process of echoing what we just keyed in doesn't hold
one's interest for long. What we need is a phone book that is held in a file. That's not difficult. We just
need to add a constructor and another method to the
PhoneBook
class:
import java.util.*;
import java.io.*;
class PhoneBook implements Serializable {
public PhoneBook() {
if(filename.exists())
try {
ObjectInputStream in = new ObjectInputStream(
new FileInputStream(filename));
