What is it?
In this article we will discuss and talk about immutability applied in Java
The concept of immutability refers to the property of objects whose state cannot be changed after they are created. This means that once an object is created, its attribute values and internal state cannot be modified, making it constant and predictable throughout its existence.
Why is the concept of immutability in Java programming so important?
The concept of immutability in Java programming (and other object-oriented programming languages) is important for several reasons, which include security, ease of reasoning, concurrency, and performance.
Security: Immutable objects cannot be changed after they are created. This prevents problems such as corrupted or inconsistent data, which can occur when multiple pieces of code change the same object simultaneously.
Easier reasoning: With immutable objects, you can rely on the fact that the state of an object will not change anywhere in the code. This makes reasoning about program behavior simpler, reducing overall complexity and avoiding unexpected side effects.
Concurrency: Immutability is especially valuable in concurrent environments, where multiple threads can access and modify shared data. If objects are immutable, there is no need for synchronization or locks to protect them, making the code safer and more efficient in terms of concurrency.
Cache and performance: Immutable objects can be easily cached as their state never changes. This can lead to significant improvements in performance, especially in operations that involve repeated calculations or frequent access to the same object.
Passing arguments: In Java, method parameters are passed by value. When a mutable object is passed as an argument, it can be changed within the method, which can lead to unexpected behavior. By using immutable objects, you ensure that the original state of the object is preserved, avoiding unwanted side effects.
To create immutable objects in Java, it is common to use the following practices:
Declare attributes as “final” so they cannot be reassigned after initialization.
Do not provide methods to modify the state of the object, only access methods to read the attribute values.
If you need to create copies of objects to make changes, you can do this using copy constructors or “clone” methods.
Stop Using Setters Methods!
In general, using immutability is a best practice for writing more robust, secure, and maintainable code, especially in complex or concurrent scenarios.
What are the disadvantages?
Although immutability brings several important advantages to Java programming, it can also have some disadvantages depending on the specific context and implementation. Some of the disadvantages include:
Memory overhead: Immutability generally involves creating copies of objects to make changes rather than modifying them directly. This can lead to increased memory consumption, especially in scenarios where there are many copy operations. In certain cases, this overhead can be significant and affect the overall performance of the program.
Cost of creating objects: When immutable objects are used extensively, the cost of creating many objects can become a performance issue, particularly in CPU-intensive situations or on resource-constrained devices.
Implementation complexity: In some cases, making an object immutable may require creating deep copies of all internal objects if they are also mutable. This can add complexity to the code and make the implementation more difficult to maintain and understand.
Limitations on some operations: Some operations that modify the state of the object may become less convenient or less efficient when working with immutable objects. For example, operations that would normally be performed in-place may now require the creation of new objects.
Large-scale updates: When dealing with a large amount of data that needs to be updated frequently, immutability can lead to a large number of copies and high memory consumption, making the update operation slower and more cumbersome.
It is important to note that not all objects in a program need to be immutable. Immutability is a recommended approach when you want to ensure that specific objects maintain a constant state over time and are protected from accidental or malicious changes.
Therefore, when deciding to use immutability in your implementation, it is essential to balance the advantages and disadvantages, and evaluate whether the approach well meets the specific requirements of the project in question. In many cases, you can intelligently combine immutable objects with mutable objects to achieve the best overall program performance and security.
How to intelligently combine immutable objects with mutable objects to achieve the best overall program performance and security?
Let’s assume we are developing a system to handle product ordering information in an online store. To exemplify how to intelligently combine immutable and mutable objects, we can create an Order class as immutable and a ShoppingCart class as mutable.
Order Class (Immutable Object):
The Order class represents a completed order and contains information about the products purchased, the customer, the total value of the order, among other details. Since a finalized order should not be changed, this class will be immutable.
public final class Order {
private final List products;
private final Customer customer;
private final double totalAmount;
public Order(List products, Customer customer, double totalAmount) {
this.products = Collections.unmodifiableList(new ArrayList<>(products));
this.customer = customer;
this.totalAmount = totalAmount;
}
// Access methods for reading attributes, but no methods for modifying the state.
}
Note that the product list is transformed into an immutable list using Collections.unmodifiableList(), to prevent it from being modified after the order is created.
ShoppingCart Class (Mutable Object):
The ShoppingCart class represents a customer’s shopping cart, where products are added or removed before completing the order. Since a shopping cart is a mutable object, let’s create methods to add and remove products.
public class ShoppingCart {
private List products;
public ShoppingCart() {
this.products = new ArrayList<>();
}
public void addProduct(Product product) {
products.add(product);
}
public void removeProduct(Product product) {
products.remove(product);
}
// Access methods for reading products, but we do not provide methods for modifying the list directly.
}
Smart Combination
To combine the immutable Order and mutable ShoppingCart objects, we can create logic that transfers the products from the shopping cart to the completed order when the customer completes the purchase.
public class OrderProcessor {
public Order createOrderFromCart(ShoppingCart cart, Customer customer) {
// Perform calculations to obtain the total order value from the products in the cart
double totalAmount = calculateTotalAmount(cart);
// Create an immutable order based on the products in the cart
return new Order(cart.getProducts(), customer, totalAmount);
}
private double calculateTotalAmount(ShoppingCart cart) {
// Implement logic to calculate the total value based on the products in the cart
// ... (calculations here)
}
}
In this example, the OrderProcessor class is responsible for processing the creation of the finished order. It receives the customer’s ShoppingCart, calculates the total order value and creates the Order immutable object based on the products present in the cart.
This way, we can take advantage of immutability by ensuring that the completed order is protected from accidental or unwanted changes, while maintaining the mutability of the shopping cart, allowing the customer to continue adding or removing products before finalizing the order.
This approach is useful for maintaining the security and integrity of final orders while providing flexibility and changeability during the purchasing process.
Most common errors
By not implementing immutability correctly, some common errors can arise, resulting in unexpected behavior and difficulties in code maintenance. Here are some examples of these errors:
Corrupted data in shared objects:
If mutable objects are shared between different parts of the code and are modified by multiple threads simultaneously, data corruption can occur, resulting in inconsistent or incorrect results.
// Example of mutable shared object without proper synchronization
class SharedData {
private List data = new ArrayList<>();
public void addData(int value) {
data.add(value);
}
public List getData() {
return data;
}
}
// Somewhere in the code:
SharedData shared = new SharedData();
shared.addData(42);
// In a different thread:
List data = shared.getData();
data.clear(); // This modifies the shared object without the other thread knowing, causing data corruption.
Unexpected side effects
When objects are mutable, it is easy to inadvertently modify their state in one part of the code and negatively affect other parts that depend on the same object.
// Example of unexpected side effect
class Calculator {
private int result;
public void add(int value) {
this.result += value;
}
public int getResult() {
return this.result;
}
}
Calculator calc = new Calculator();
calc.add(5);
int result1 = calc.getResult(); // result1 = 5
calc.add(10);
int result2 = calc.getResult(); // result2 = 15, but result1 is still 5
Difficulties tracking state: With mutable objects, it can be difficult to track when and where an object has been modified, especially in complex or long-running code. This makes debugging and maintenance more challenging.
Caching issues and optimizations: If objects are mutable and widely used, cache optimization techniques may become less effective as information may change unpredictably.
Difficulties with Concurrency: In concurrent environments, mutable objects can be problematic, requiring manual synchronization or resulting in race conditions and indeterminate results.
Conclusion
In general, immutability avoids many of the problems mentioned above, providing more security and predictability to the code. Therefore, it is recommended to use immutable objects whenever possible and ensure that mutable objects are properly protected and synchronized across concurrent environments.
4 de February de 2024
