Advertisement

---

Top

< Prev

Next >

What is "transient" in Java?

In Java, transient is a keyword. When an object is being serialized, its instance variables which are declared with the transient keyword are skipped by the process of serialization i.e. when an object is serialized by the process of serialization, the state of transient instance variables of this object is not saved.

Why "transient" keyword is used?

In some situations when an object is serialized, we may not want to save the state of a few unimportant instance variables of an object. In this case, we only need to declare these instance variables with the transient keyword.

What happens to an instance variable with "transient" keyword in Serialization?

After an object's state is saved by the process of serialization, when this saved object is deserialized, its instance variables marked with the transient keyword are assigned their default values. Let us take a look at the different instance variable types and their default values.

Instance variable type	Default value
boolean	false
byte, short, int, long	zero
float,double	0.0
character	'\u0000'
Object reference variable	null

Such default values are implicitly given to the transient declared instance variables of an object during deserialization.

Advertisement

Let's understand "transient" with an example -:

//Java - Example of transient keyword 


import java.io.*;

//A class implementing Serializable interface 
class TransientExm implements Serializable	
{
transient int i=10;	//instance variable of primitive int type is marked "transient"
public static void main(String... ar)
{
TransientExm ob= new TransientExm();
System.out.println("Before Serialization object has value : " + ob.i);
try
{
	//Writing saved state of the object in this file
	FileOutputStream fos= new FileOutputStream("E:\\File.ser");
	ObjectOutputStream oos= new ObjectOutputStream(fos);
	
	//Serializing, i.e. saving the state of this object, ob
	oos.writeObject(ob);	
	oos.close();
}
catch(Exception exp)
{
	System.out.println(exp);
}

try
{
	//Reading the same file for Deserialization
	FileInputStream fis= new FileInputStream("E:\\File.ser");	
	ObjectInputStream ois= new ObjectInputStream(fis);
	
	//Deserializing, i.e. restoring the object to its original state.
	ob=(TransientExm)ois.readObject();	
	ois.close();
	System.out.println("After Deserialization restored object has value : "+ ob.i);
}
catch(Exception exp)
{
	System.out.println(exp);
}


}

}

Output is -:

Before Serialization object has value : 10
After Deserialization restored object has value : 0

Program Analysis

• In the code above, we are first performing the serialization of an object by saving its state, without saving the state of its instance variable which is marked with the transient keyword.
• This instance variable has a value 10 at the time of serialization of the object.
• Finally, when this object is then deserialized, its instance variable(which is a primitive type - int) is initialized to its default value, zero, and its value 10 at the same of serialization is lost.

Please share this article -

< Prev

Next >

< What is Serialization?

Static in Serialization >

Advertisement