Java Reference
In-Depth Information
Of course, you can try it with several entries if you have the stamina.
How It Works
The values in the map that represents a phone book are
BookEntry
objects to allow for more information
to be stored about a person. If you wanted to keep it really simple, you could use
PhoneNumber
objects
as values in the map.
The
main()
method runs an ongoing loop that continues 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 is added to the
HashMap
member of the
PhoneBook
object.
If a
2
is entered, the
getEntry()
method is called. The
readPerson()
member of the
Person
class is
called 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
is returned, so you have to check for it and display an appropriate message.
String
comparisons are case sensitive so searching for “algernon lickspittle" will not find an entry. You
could convert both strings to the same case if you wanted to have comparisons that were not case sensit-
ive.
TRY IT OUT: Storing a Map in a File
This phone book is not particularly useful. The process of echoing what you just keyed in doesn't hold
one's interest for long. What you need is a phone book that is held in a file. That's not difficult. You just
need to add a constructor and another method to the
PhoneBook
class:
import java.nio.file.*;
import java.io.*;
import java.util.*;
class PhoneBook implements Serializable {
public PhoneBook() {
if(Files.exists(file)) {
// If there's a phone
book in a file...
try (ObjectInputStream in = new ObjectInputStream(
new
BufferedInputStream(Files.newInputStream(file)))){
phonebook = (HashMap<Person, BookEntry>)in.readObject();
//...read it in.
} catch(ClassNotFoundException| IOException e) {
e.printStackTrace();
System.exit(1);
}
