In this example, we will learn to create an immutable class in Java.

Java Immutable Class

In Java, when we create an object of an immutable class, we cannot change its value. For example, String is an immutable class. Hence, we cannot change the content of a string once created.

Besides, we can also create our own custom immutable classes. Here’s what we need to do to create an immutable class.

• declare the class as final so it cannot be extended
• all class members should be private so they cannot be accessed outside of class
• shouldn’t contain any setter methods to change the value of class members
• the getter method should return the copy of class members
• class members are only initialized using constructor

Example: Java program to create immutable class

// class is declared final
final class Immutable {

  // private class members
  private String name;
  private int date;

  Immutable(String name, int date) {

    // class members are initialized using constructor
    this.name = name;
    this.date = date;
  }

  // getter method returns the copy of class members
  public String getName() {
    return name;
  }

  public int getDate() {
    return date;
  }

}

class Main {
  public static void main(String[] args) {

    // create object of Immutable
    Immutable obj = new Immutable("Programiz", 2011);

    System.out.println("Name: " + obj.getName());
    System.out.println("Date: " + obj.getDate());
  }
}

Output

Name: Programiz
Date: 2011

In the above example, we have created an immutable class named Immutable.

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