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Transient Keyword in Java: What It Is & How It Works

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In Java language, the transient keyword is an essential part of serialization. Serialisation converts an object’s state into a format that can be stored or transmitted, typically as a file or stream. Java serialization is achieved using the serialisable interface and related classes. The transient keyword is a variable modifier in Java that is used in the context of serialization. This article explained the transient keyword to you.

Introduction to Transient Keyword in Java

In Java, the transient keyword indicates that a particular field should not be serialized. When you serialize an object, the Java language converts it into a byte stream to save it to a file or send it over a network.

transient keyword in java

How to Use Transient Keywords in Java?

The transient keyword indicates that a field should not be serialized when an object is converted into a byte stream (for example, when saving an object to a file or sending it over a network). It is very useful for fields that contain sensitive or derived values that do not need to be persisted.

class Main{

public static void main(String args[]){

// Code

transient String password ;

}

}

The following program demonstrates the transient keyword example.

Program

import java.io.Serializable;

import java.io.FileOutputStream;

import java.io.ObjectOutputStream;

import java.io.FileInputStream;

import java.io.ObjectInputStream;

import java.io.IOException;

import java.util.Date; 

public class Employee implements Serializable { 

String firstName;

String secondName;

transient String fullName;

String email;

String password;

Date dob; 

/*

Constructor

*/

Employee(

String firstName,

String secondName,

String email,

String password,

Date dob

) {

this.firstName = firstName;

this.secondName = secondName;

this.email = email;

this.password = password;

this.dob = dob;

this.fullName = firstName + " " + secondName;

} 

public static void main(String[] args) {

Employee student = new Employee(

"Harry",

"Potter",

"harrt.potter@gmail.com",

"12345@Nk",

new Date()

); 

serialize(student);

deserialize();

} 

private static void serialize(Employee student) {

try {

System.out.println("Student serializing: " + student.toString());

FileOutputStream fileOut = new FileOutputStream("student.ser");

ObjectOutputStream out = new ObjectOutputStream(fileOut);

out.writeObject(student);

out.close();

fileOut.close();

} catch (IOException i) {

i.printStackTrace();

}

} 

private static void deserialize() {

try {

FileInputStream fileIn = new FileInputStream("student.ser");

ObjectInputStream in = new ObjectInputStream(fileIn);

Employee student = (Employee) in.readObject();

in.close();

fileIn.close();

System.out.println("Student deserialized: " + student.toString());

} catch (IOException | ClassNotFoundException i) {

i.printStackTrace();

}

} 

@Override

public String toString() {

return (

"Student{" +

"firstName='" +

firstName +

''' +

", secondName='" +

secondName +

''' +

", fullName='" +

fullName +

''' +

", email='" +

email +

''' +

", password='" +

password +

''' +

", dob=" +

dob +

'}'

);

}

}

Output

Student serializing: Student{firstName='Harry', secondName='Potter', fullName='Harry Potter', email='harrt.potter@gmail.com', password='12345@Nk', dob=Thu Sep 19 10:43:58 IST 2024}

Student deserialized: Student{firstName='Harry', secondName='Potter', fullName='null', email='harrt.potter@gmail.com', password='12345@Nk', dob=Thu Sep 19 10:43:58 IST 2024}

After running the following code, a new file named employee.str is generated in the project, which represents the serialized object.

We can use the transient keyword with the fullName variable. When we deserialize the object and inspect the result, we see that the fullName field is null.

Usage of Transient Keywords in Java

The transient modifier is used to secure the variables. Serialization creates a persistent file. If the object contains passwords or security keys, everything will be saved on the disk, which is not a good sign of a secure system. However, there might be some variables that you do not want to serialize—these are typically sensitive data, derived values, or any data that is not necessary for reconstructing the object. This is where the transient keyword comes into the play.

The password variable is critical data, so serialization must be avoided. To skip serialization, we can use the transient keyword in Java.

String firstName;

String secondName;

transient String fullName;

String email;

transient String password;

Date dob;

How to Use Transient with Final Keyword?

The transient with the final keyword does not affect the serialization because variables declared as final are serialized directly by their values. The final keyword is used to declare constants or restrict the modification of variables, methods, or classes. When we declare the field as final, it can only be assigned once and cannot be changed afterward. It means that the field will not be serialized but its value will remain the same even after deserialization. So, If a field is declared as final, its value will remain the same regardless of whether the object is serialized or not.

Difference between Transient and Volatile Keywords in Java

The following table differentiates the transient and volatile keywords in Java language.

Feature	transient	volatile
Purpose	It prevents serialization of a field	It ensures the visibility of changes to variables across threads
Use Case	It is used in serialization(eg ObjectOutputStream)	It used multithreading for shared variables.
Effect	The field is not saved during object serialization	It changes the variable are visible to all threads immediately.
Thread Safety	It does not provide thread safety	It provides limited form of thread safety by ensuring visibility
Keyword Usage	Transient is used before the field type	Volatile is used before the variable type.

Conclusion

In this article, we learned about the transient keyword in Java language. This keyword is a crucial feature in Object serialization to indicate that certain fields should not be included in the serialized representation of an object. It is particularly useful for protecting sensitive data, such as passwords, ensuring that non-serializable objects are excluded, and avoiding the serialization of large, resource-intensive fields like file streams. This selective serialization enhances control over data persistence, allowing developers to manage what information is stored, thereby improving security and performance in Java applications. Overall, the transient keyword is essential for effective and secure object serialization.

FAQs

What is the purpose of the transient keyword in Java?

The transient keyword indicates that a particular field should not be serialized when an object is converted into a byte stream. This is useful in excluding sensitive information or non-serializable objects.

Can a class with transient fields implement the Serializable interface?

Yes, a class can implement the Serializable interface and still contain transient fields. Only the non-transient fields will be serialized.

Can I use transient with enums?

Yes, we can mark fields of enum types as transient. During serialization these fields will be ignored.

Can a class with transient fields be serialized?

Yes, a class can still be serialized even with transient fields. Only the non-transient fields will be serialized.

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