Immutable Class in Java

In this post on Immutable class in Java, we will explore into the characteristics that define these classes, the benefits they bring, and how to create them.

Table of Contents

What is Immutable Class in Java ?

An immutable class in Java is one whose instances cannot be changed after they have been created. This means that once an immutable class object is formed, its internal state cannot be altered. This design pattern ensures that objects are thread-safe, have predictable behavior, and may be safely shared among several threads without the danger of unanticipated changes.

The very common example is String class. Also all wrapper classes like Integer, Long are immutable.

How to Create Immutable Class in Java?

For creating an immutable class in Java, we need to do the following things:

1. Make the class final

2. Make all the fields private and final.

3.Don’t provide any method that allows to change the values of the fields. For example don’t have any setter methods.Only getters should be there.

Java Code

Let’s write the code to implement Immutable Class in Java.

public final class ImmutablePerson {
    private final String name;
    private final int age;

    public ImmutablePerson(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }
}

In this example, the ImmutablePerson class has final fields, a constructor for initialization, and getter methods to access the fields. Once an instance is created, its state cannot be modified.

Benefits of Immutable Class in Java

Let’s look into the advantages that immutable classes bring to the table:

Thread Safety: Immutable classes inherently possess thread safety. As their state cannot be modified after creation, there’s no need for complex synchronization mechanisms.
Predictable Behavior: With immutability, an object’s state remains constant throughout its lifecycle. This predictability guarantees that an object’s behavior won’t unexpectedly change due to external influences, leading to more reliable and bug-free code.
Caching Efficiency: Immutable objects are ideal candidates for caching. Since their state is fixed, they can be cached and shared across different parts of an application without fear of modification.
Simplicity and Maintainability: Immune to the complexities of mutable state, code based on immutable classes becomes simpler to write, read, and maintain.
Functional Programming Advantages: Immutable classes align seamlessly with functional programming principles. They facilitate writing pure functions, as function behavior is solely determined by inputs without side effects.
Consistent Hashing and Equality: Immutable classes maintain consistent hash codes and equality checks throughout their lifecycle. This ensures reliable usage in data structures like collections and hash maps.
Global Stability: Objects of immutable classes, once created, are not influenced by external factors. This makes them ideal for representing constants, configuration settings, and shared resources, ensuring consistency across the entire application.
Resilience to Malicious Attacks: Immutable classes provide a level of protection against certain types of attacks, like unauthorized modification of objects, making your codebase more secure.

Use Cases and Scenarios: Immutable Class in Java

Let’s explore some of the most use cases where we can use Immutable Classes:

Multithreaded Environments: In applications with concurrent access from multiple threads, mutable state can lead to synchronization challenges and race conditions. Immutable classes offer a solution by ensuring that objects remain unchanged, eliminating the need for complex synchronization mechanisms.
Functional Programming: Immutable classes are a natural fit for functional programming paradigms, where functions avoid side effects and rely on immutable data. They enable you to write pure functions without the worry of altering object state.
Caching: Immutable objects are ideal for caching, as they can be safely shared among different parts of an application without risk. This is particularly useful for frequently used data that doesn’t change often.
Configuration Settings: Configuration settings, such as those used in frameworks, are excellent candidates for immutability. Once set, these values remain constant throughout the application’s execution.
Value Types: Objects that represent values, like coordinates, dates, or currency amounts, benefit from immutability. This prevents unintended changes that could lead to data corruption.
Immutable Collections: Immutable collections provide a snapshot of data at a particular point in time, which can be useful for scenarios where data integrity is crucial, such as audit trails or historical records.
Domain Objects: In domain-driven design, entities that represent fundamental concepts in your application’s domain can often be made immutable. This ensures the integrity of those concepts throughout the application’s lifecycle.
Shared Resources: Resources like database connections, network sockets, or other shared components can be encapsulated in an immutable object to prevent accidental changes or unauthorized modifications.
Flyweight Design: Immutable classes can be used as flyweight objects, representing shared, reusable instances in memory. This reduces memory consumption by avoiding the creation of duplicate objects.
Serialization and Deserialization: Immutable objects simplify the serialization and deserialization process. Since their state doesn’t change, you can ensure consistent data representation across different environments.

Best Practices: Immutable Class in Java

Let’s explore the best practices for using immutable Class in Java.

Memory Consumption: Although immutability guarantees consistency, it can lead to increased memory consumption when creating new instances for every modification. Balance memory efficiency with immutability, considering object frequency and data size.
Performance Implications: Creating new instances might seem performance-intensive. Employ techniques like object pooling or instance reuse where feasible to optimize memory usage and reduce object creation overhead.
Effective Constructor Design: Immutable classes often rely on constructors for initializations. Design constructors to accept all necessary parameters and initialize all final fields to ensure completeness.
Avoid Excessive Chaining: Chaining constructors excessively might lead to confusion and errors. Consider using builder patterns for more complex objects to improve readability and maintainability.
Immutable State: Ensure that the state of all fields remains unmodified after construction. Prevent even internal methods from altering the state to maintain the integrity of the object.
Consistency in Equals and HashCode: Implement equals and hashCode methods consistently to maintain reliable behavior in collections and comparison operations.
Serialization and Deserialization: Immutable classes simplify serialization and deserialization, but be cautious when evolving your class structure over time to maintain backward compatibility.
Avoid Mixing Mutable and Immutable Objects: Mixing mutable and immutable objects in the same context can lead to unexpected behaviors. If possible, work within a consistent paradigm to prevent confusion.
Cloning and Copying: Be cautious with cloning or copying immutable objects, as it may lead to unnecessary memory consumption and performance issues. Usually, there’s little need for this due to immutability.
Limit Fields: Limit the number of fields in your immutable classes. Too many fields can complicate the constructor and hinder the readability of your code.
Inheritance: If designing an inheritance hierarchy with immutable classes, ensure that derived classes maintain immutability principles to avoid unexpected behavior.
Immutability vs. Primitives: In some cases, using primitives (like int, char, etc.) might be more efficient than wrapping them in immutable classes.

Conclusion: Immutable Class in Java

In this comprehensive article, we explored the intricate world of immutable class in Java. We looked into the core principles, benefits, use cases, and best practices surrounding this essential design pattern.