What is transient variable in Java
transient variable in Java is a variable whose
value is not serialized during Serialization and which is initialized by its
default value during de-serialization, for example for object transient variable it would be null. this
behavior can be customized by using Custom Serialized form or by using Externalizable
interface. transient variable is used to prevent any
object from being serialized and you can make any variable transient by using transient keyword. By the way difference
between transient and volatile
variable in Java is a famous Java
interview question but transient
variable is completely different than volatile variable which we have discussed
in our post What
is volatile variable in Java. In next section we will see complete example
of serialization where we will first serialize an instance of Book class which
implements Serializable and than de-serialize to see What is
the value of transient variable after deserialization.
How to use transient variable in Java - Serialization Example
Here is a
complete code example of Serialization in Java which demonstrate How
to use transient variable in
Java program; transient variables are not serialized during Serialization process and initialize with default
value during deserialization.
package test;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
/**
*
* Java program to demonstrate What is transient variable in Java and fact that value of
* transient variable is not serialized and during serialization it initialized with
* default value of that data type. e.g. If transient variable is Object than after
* deserialization its value would be null.
*
* @author Javin
*/
public class TransientTest {
public static void main(String args[]) {
Book narnia = new Book(1024, "Narnia", "unknown", 2);
System.out.println("Before Serialization: " + narnia);
try {
FileOutputStream fos = new FileOutputStream("narnia.ser");
ObjectOutputStream oos = new ObjectOutputStream(fos);
oos.writeObject(narnia);
System.out.println("Book is successfully Serialized ");
FileInputStream fis = new FileInputStream("narnia.ser");
ObjectInputStream ois = new ObjectInputStream(fis);
Book oldNarnia = (Book) ois.readObject();
System.out.println("Book successfully created from Serialized data");
System.out.println("Book after seriazliation : " + oldNarnia);
} catch (Exception e) {
e.printStackTrace();
}
}
}
/*
* A class which implements Serializable interface and has a transient variable.
*/
class Book implements Serializable{
private int ISBN;
private String title;
private String author;
private transient int edition = 1; //transient variable not serialized
public Book(int ISBN, String title, String author, int edition) {
this.ISBN = ISBN;
this.title = title;
this.author = author;
this.edition = edition;
}
@Override
public String toString() {
return "Book{" + "ISBN=" + ISBN + ", title=" + title + ", author=" + author + ", edition=" + edition + '}';
}
}
Output:
Before Serialization: Book{ISBN=1024, title=Narnia, author=unknown, edition=2}
Book is successfully Serialized
Book successfully created from Serialized data
Book after seriazliation : Book{ISBN=1024, title=Narnia, author=unknown, edition=0}
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
/**
*
* Java program to demonstrate What is transient variable in Java and fact that value of
* transient variable is not serialized and during serialization it initialized with
* default value of that data type. e.g. If transient variable is Object than after
* deserialization its value would be null.
*
* @author Javin
*/
public class TransientTest {
public static void main(String args[]) {
Book narnia = new Book(1024, "Narnia", "unknown", 2);
System.out.println("Before Serialization: " + narnia);
try {
FileOutputStream fos = new FileOutputStream("narnia.ser");
ObjectOutputStream oos = new ObjectOutputStream(fos);
oos.writeObject(narnia);
System.out.println("Book is successfully Serialized ");
FileInputStream fis = new FileInputStream("narnia.ser");
ObjectInputStream ois = new ObjectInputStream(fis);
Book oldNarnia = (Book) ois.readObject();
System.out.println("Book successfully created from Serialized data");
System.out.println("Book after seriazliation : " + oldNarnia);
} catch (Exception e) {
e.printStackTrace();
}
}
}
/*
* A class which implements Serializable interface and has a transient variable.
*/
class Book implements Serializable{
private int ISBN;
private String title;
private String author;
private transient int edition = 1; //transient variable not serialized
public Book(int ISBN, String title, String author, int edition) {
this.ISBN = ISBN;
this.title = title;
this.author = author;
this.edition = edition;
}
@Override
public String toString() {
return "Book{" + "ISBN=" + ISBN + ", title=" + title + ", author=" + author + ", edition=" + edition + '}';
}
}
Output:
Before Serialization: Book{ISBN=1024, title=Narnia, author=unknown, edition=2}
Book is successfully Serialized
Book successfully created from Serialized data
Book after seriazliation : Book{ISBN=1024, title=Narnia, author=unknown, edition=0}
If you look
at this example of Serializing Object in
Java you will realize that value of transient variables are not serialized and persisted and during
deserialization those value are initialized with there default value which is zero
in case of int variable. Since constructor also didn't run during
de-serialization it won't get the value provided during constructor. In Summary
use transient variable carefully in Java.
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