Files, Streams and Object Serialization - Java: How to Program Early Objects - page 665

64 // set balance

65 public void setBalance( double balance)

66 {

67

this .balance = balance;

68

}

69
70

// get balance

71

public double getBalance()

72

{

73

return balance;

74

}

75

} // end class Account

Fig. 15.9 | Account class for serializable objects. (Part 3 of 3.)

In a Serializable class, every instance variable must be Serializable . Non- Seri-
alizable instance variables must be declared transient to indicate that they should be
ignored during the serialization process. By default, all primitive-type variables are serializ-
able. For reference-type variables, you must check the class's documentation (and possibly
its superclasses) to ensure that the type is Serializable . For example, String s are Seri-
alizable . By default, arrays are serializable; however, in a reference-type array, the refer-
enced objects might not be. Class Account contains private data members account ,
firstName , lastName and balance —all of which are Serializable . This class also pro-
vides public get and set methods for accessing the private fields.

Writing Serialized Objects to a Sequential-Access File
Now let's discuss the code that creates the sequential-access file (Fig. 15.10). We concen-
trate only on new concepts here. To open the file, line 27 calls Files static method
newOutputStream , which receives a Path specifying the file to open and, if the file exists,
returns an OutputStream that can be used to write to the file. Existing files that are opened
for output in this manner are truncated . There is no standard filename extension for files
that store serialized objects, so we chose the .ser .

1 // Fig. 15.10: CreateSequentialFile.java

2 // Writing objects sequentially to a file with class ObjectOutputStream.

3 import java.io.IOException;

4
5

import java.io.ObjectOutputStream;

import java.nio.file.Files;

6 import java.nio.file.Paths;

7 import java.util.NoSuchElementException;

8 import java.util.Scanner;

9
10 public class CreateSequentialFile

11 {

12 private static ObjectOutputStream output; // outputs data to file

13

Fig. 15.10 | Sequential file created using ObjectOutputStream . (Part 1 of 3.)