How to create the immutable class in Java?

An immutable class object's properties cannot be modified after initialization. For example String is an immutable class in Java. We can create a immutable class by following the given rules below.

• Make class final − class should be final so that it cannot be extended.

• Make each field final − Each field should be final so that they cannot be modified after initialization.

• Create getter method for each field. − Create a public getter method for each field. fields should be private.

• No setter method for each field. − Do not create a public setter method for any of the field.

• Create a parametrized constructor − Such a constructor will be used to initialize properties once.

In following example, we've created a immutable class Employee.

Example

 Live Demo

public class Tester {
   public static void main(String[] args) {
      Employee e = new Employee(30, "Robert");
      System.out.println("Name: " + e.getName() +", Age: " + e.getAge());
   }
}
final class Employee {
   final int age;
   final String name;
   Employee(int age, String name) {
      this.age = age;
      this.name = name;
   }
   public int getAge() {
      return age;
   }
   public String getName() {
      return name;
   }
}

Output

Name: Robert, Age: 30