Transient Keyword in Java

Last Updated: 04 October, 2023

Prerequisite : Serialization and Deserialization in Java

In Java, the transient is a modifier used in the serialization process. At the time of serialization, if we don’t want to serialize any particular variables of a class, then we use the transient keyword with those variables. When the JVM finds a variable as a transient variable, it ignores the original value of the variable and assigns the default value of that variable's data type.

In order to meet security constraints, transient keywords are very important.

The process of converting an object into a byte stream is known as Serialization, and its reverse process is known as Deserialization in Java.
The entire process of Serialization and Deserialization is platform-independent.

Let's understand the uses of transient keywords with the help of a given sample Java program.

Example 1 : Using transient keyword in a Java Program

import java.io.*; class Employee implements Serializable { // Normal Variables int empID = 101; String name = "Ganesh"; // Transient Variables transient String loginId = "testLoginId"; transient String password = "password123"; } public class TransientKeywordExample { public static void main(String args[]) throws Exception { Employee emp = new Employee(); // Serialization - Writing Employee object into the file FileOutputStream fos = new FileOutputStream("employee.ser"); ObjectOutputStream out = new ObjectOutputStream(fos); out.writeObject(emp); out.flush(); out.close(); fos.close(); System.out.println("Employee object successfully serialized"); System.out.println("Deserlized Object Employee values:"); // DeSerialization - Preparing Employee Object ObjectInputStream in = new ObjectInputStream(new FileInputStream("employee.ser")); Employee empObj = (Employee) in.readObject(); System.out.println("EmpID: " + empObj.empID + "\nName: " + empObj.name + "\nLoginID: " + empObj.loginId + "\nPassword: " + empObj.password); in.close(); } }

In the above example, Employee class has two confidential properties named loginId and password. These properties we don't want to serialize that's why they are declared as transient, which means that at the time of serialization, the JVM will assign a default value (String default value is null) to these two variables, not the actual value.

Output

Employee object successfully serialized
Deserlized Object Employee values:
EmpID: 101
Name: Ganesh
LoginID: null
Password: null

Using transient keyword with static variables

Static variables belong to a particular class, not to instances of that class. If we serialize the instance, then only instance variables will be serialized, not static variables. If we don't want to serialize the instance variable, we declare the instance variable as transient.

But if we declare transients with static variables, then there will be no impact and no use either. It will not give any compilation errors while compiling the code.

If a variable is defined as static and transient, then a static modifier will govern the behavior of the variable but not the transient.

Here is an example of transient keyword with static variables:

Example 2 : Using transient keyword with static in a Java Program

import java.io.*; class Employee implements Serializable { // Normal Variables int empID = 101; String name = "Ganesh"; // Static Variable static String department = "Human Resource"; // Static and Transient Variable static transient float ctc = 10.5f; // Transient Variable transient int totalYearsOfExp = 5; } public class TransientWithStaticExample { public static void main(String args[]) throws Exception { Employee emp = new Employee(); Employee.ctc = 15.5f; // Serialization - Writing Employee object into the file FileOutputStream fos = new FileOutputStream("employee.ser"); ObjectOutputStream out = new ObjectOutputStream(fos); out.writeObject(emp); out.flush(); out.close(); fos.close(); System.out.println("Employee object successfully serialized"); System.out.println("Deserlized Object Employee values:"); // DeSerialization - Preparing Employee Object ObjectInputStream in = new ObjectInputStream(new FileInputStream("employee.ser")); Employee empObj = (Employee) in.readObject(); System.out.println("EmpID: " + empObj.empID + "\nName: " + empObj.name + "\nDepartment: " + empObj.department + "\nCTC: " + empObj.ctc + "\nTotal Years of Experience: " + empObj.totalYearsOfExp); in.close(); } }

Output

Employee object successfully serialized
Deserlized Object Employee values:
EmpID: 101
Name: Ganesh
Department: Human Resource
CTC: 15.5
Total Years of Experience: 0

Using transient keyword with final variables

Using transient with the final keyword doesn’t have an impact on serialization as the variables declared final are directly serialized by their values. The JVM will assign the original value of those variables (declared transient and final, both).

Let's understand it with the help of the example given below.