Java Reference
In-Depth Information
The
ObjectOutputStream
constructor and all methods that write data to an object output
stream throw
IOException
objects. These must be accounted for using a
try
-
catch
block or a
throws
clause.
Listing 16.1 contains a Java application that consists of two classes:
ObjectWriter
and
Message
. The
Message
class represents an email message. This class has
from
and
to
objects that store the names of the sender and recipient, a
now
object that holds a
Date
value representing the time it was sent, and a
text
array of
String
objects that holds the
message. There also is an
int
called
lineCount
that keeps track of the number of lines
in the message.
16
When designing a program that transmits and receives email, it makes sense to use some
kind of stream to save these messages to disk. The information that constitutes the mes-
sage must be saved in some form as it is transmitted from one place to another; it also
might need to be saved until the recipient is able to read it.
Messages can be preserved by saving each message element separately to a byte or char-
acter stream. In the example of the
Message
class, the
from
and
to
objects could be writ-
ten to a stream as strings, and the
text
object could be written as an array of strings. The
now
object is a little trickier because there isn't a way to write a
Date
object to a charac-
ter stream. However, it could be converted into a series of integer values representing
each part of a date: hour, minute, second, and so on. Those could be written to the
stream.
Using an object output stream makes it possible to save
Message
objects without first
translating them into another form.
The
ObjectWriter
class in Listing 16.1 creates a
Message
object, sets up values for its
variables, and saves it to a file called
Message.obj
via an object output stream.
LISTING 16.1
The Full Text of
ObjectWriter.java
1: import java.io.*;
2: import java.util.*;
3:
4: public class ObjectWriter {
5: public static void main(String[] arguments) {
6: Message mess = new Message();
7: String author = “Sam Wainwright, London”;
8: String recipient = “George Bailey, Bedford Falls”;
9: String[] letter = { “Mr. Gower cabled you need cash. Stop.”,
10: “My office instructed to advance you up to twenty-five”,
11: “thousand dollars. Stop. Hee-haw and Merry Christmas.” };
12: Date now = new Date();
13: mess.writeMessage(author, recipient, now, letter);
