Mutable Class in Java

In the world of object-oriented programming, the concept of immutability is often emphasized for its benefits in terms of code stability and predictability. However, there are situations where mutable classes play a crucial role, providing flexibility and the ability to modify object state. In Java, a mutable class allows its instances to be modified after creation, offering a different programming paradigm compared to immutable classes. In this section, we will discuss the concept of mutable classes in Java, their characteristics, advantages, and best practices.

What is a Mutable Class?

In Java, a mutable class is a class whose instances can be modified after they are created. It means that the state of the object can change through various methods and operations during its lifetime. Unlike immutable classes, where instances are fixed upon creation and cannot be modified, mutable classes offer flexibility and dynamic behavior.

Characteristics of Mutable Classes

• State Modification: The primary characteristic of mutable classes is that they allow modifications to their internal state. This can be achieved by exposing public methods that update the object's fields or properties. By allowing such modifications, mutable classes provide the ability to change the state of an object dynamically.
• Mutability Across Instances: Unlike immutable classes, where all instances share the same state, mutable classes can have different states across different instances. Each object maintains its own state, making it possible to have multiple objects of the same class with varying values.

Advantages of Mutable Classes

• Flexibility and Dynamic Behavior: Mutable classes allow developers to change the state of an object during runtime. This flexibility can be beneficial in scenarios where frequent modifications are required. For example, when working with complex data structures or building systems with dynamic requirements, mutable classes offer the necessary flexibility to accommodate changes.
• Performance and Memory Efficiency: Mutable classes can provide performance benefits in certain scenarios. When dealing with large datasets, it can be more efficient to modify an existing object rather than creating a new one from scratch. By reusing existing instances, the memory footprint and processing overhead can be reduced.
• Simplified Coding: Mutable classes can simplify the coding process by eliminating the need to create new objects for every state change. This can lead to cleaner and more concise code, as it avoids the complexities associated with managing immutable objects and their copies.

Using Mutable Classes

• Encapsulation: It is important to maintain proper encapsulation when designing mutable classes. Encapsulation ensures that the internal state of an object is protected from direct access and modification by external code. By encapsulating data and providing controlled access through getter and setter methods, you can maintain better control over the object's state.
• Consistency and Thread Safety: When working with mutable classes, it is crucial to ensure consistency and thread safety. In multi-threaded environments, concurrent modifications to mutable objects can lead to unexpected behavior and data corruption. Proper synchronization mechanisms, such as locks or concurrent data structures, should be employed to ensure thread safety.
• Documentation and Communication: As mutable classes allow modifications to object state, it is important to document and communicate the intended usage and limitations of these classes. Clearly specify which methods are responsible for modifying the state and any potential side effects that may occur. This helps other developers understand how to use the class correctly and avoid unintended consequences.
• Consider Immutability: While mutable classes have their advantages, it's essential to evaluate whether immutability might be a better fit for certain scenarios. Immutability ensures thread safety by eliminating the need for synchronization and reduces the risk of accidental modifications. Evaluate the trade-offs and make an informed decision based on the specific requirements of your project.

How to Create a Mutable Class?

The following two things are essential for creating a mutable class:

• Methods for modifying the field values
• Getters and Setters of the objects

Consider the below example of the mutable class:

MutableExample.java

Output:

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In the above example, we are changing the name value using the setName() method.

Mutable classes in Java provide the ability to modify object state after creation, offering flexibility and dynamic behavior. While immutability is often recommended for its benefits in terms of code stability and predictability, mutable classes have their own advantages in certain scenarios. They allow for flexibility, dynamic behavior, and improved performance and memory efficiency. It is also important to consider whether immutability might be a better fit for certain scenarios. Immutability ensures thread safety, eliminates the need for synchronization, and reduces the risk of accidental modifications. Evaluating the trade-offs and making an informed decision based on the specific requirements of your project is key.