You need to ensure that certain data within your application remains constant and secure throughout its lifecycle. (Immutability)

Question

Accepted Answer

Immutability is a design principle where an object's state cannot be modified after it is created. Once initialized, the data remains unchanged throughout its lifetime. This approach improves application reliability, thread safety, and security by preventing unintended or unauthorized modifications.

Key Points:
• Immutable objects guarantee that their state remains constant after creation.
• They are inherently thread-safe because multiple threads can access them without synchronization.
• Immutability helps prevent bugs caused by accidental data modification and improves code predictability.

Example:
A user's Account Number or Aadhaar Number should not change after creation. By making these values immutable, you ensure their integrity and prevent accidental updates during application execution.

Code Example:
```
final class Employee {

private final int id;
    private final String name;

public Employee(int id, String name) {
        this.id = id;
        this.name = name;
    }

public int getId() {
        return id;
    }

public String getName() {
        return name;
    }
}
```
Interview Tip:
A concise interview answer is: Immutability means an object's state cannot be changed after it is created. It is achieved using final fields, no setter methods, and controlled object construction. Immutable objects improve security, thread safety, and application stability by preventing unintended modifications.