Creating an immutable object in Java means creating an object whose state cannot be changed after it is constructed. To achieve immutability, follow these principles:

1. Declare the class as final so that it cannot be subclassed.

2. Make all fields private and final to ensure they are not modified after the object is constructed.

3. Provide only getters for the fields, and no setters.

4. Ensure that any mutable fields are deeply copied to prevent modification through references.

https://raw.githubusercontent.com/vsaravanan/java22/master/src/main/java/com/saravanjs/java22/console/corejava/Immutable.java

final class Person {
private final String name;
private final int age;
private final Date birthDate;

public Person(String name, int age, Date birthDate) {
this.name = name;
this.age = age;
// Create a defensive copy of the mutable Date object
this.birthDate = new Date(birthDate.getTime());
    }

public String getName() {
return name;
    }

public int getAge() {
return age;
    }

public Date getBirthDate() {
// Return a defensive copy of the mutable Date object
return new Date(birthDate.getTime());
    }
}
public class Immutable {
public static void main(String[] args) {
Date birthDate = new Date();
Person person = new Person("John Doe", 30, birthDate);

System.out.println("Name: " + person.getName());
System.out.println("Age: " + person.getAge());
System.out.println("Birth Date: " + person.getBirthDate());

// Attempt to modify the birthDate object
birthDate.setTime(0);
System.out.println("Variable : " + birthDate);

// Verify that the birthDate inside Person is not affected
System.out.println("Modified Birth Date: " + person.getBirthDate());
    }
}

Name: John Doe

Age: 30

Birth Date: Mon Jun 17 23:06:06 SGT 2024

Variable : Thu Jan 01 07:30:00 SGT 1970

Modified Birth Date: Mon Jun 17 23:06:06 SGT 2024