1. Introduction
In our journey as Java programmers, we often encounter a crucial keyword that plays a significant role in making our code more secure and stable – the final keyword. Mastering this keyword allows us to prevent unwanted modifications and promote safer, cleaner code.
Throughout this article, we will delve into the various ways to use the final keyword effectively in Java, including applying it to variables, methods, and even classes. By the end of our discussion, you will understand when and how to employ the final keyword to help you write more robust and reliable code.
2. Understanding the Final Keyword in Java
We use the final keyword in Java for a variety of purposes. It allows us to make variables, methods, and classes constant or non-modifiable, depending on the context in which it is used. In this section, let’s dive into the different uses of the final keyword and see some examples.
First, let’s look at how to use the final keyword with variables. When a Java final variable is declared, its value cannot be changed once it has been initialized. This is particularly helpful for declaring constants that should not be modified. For example:
final double PI = 3.14159;
In the above code example, we define a final variable named PI and assign it the value of 3.14159. This value cannot be changed throughout the program, and any attempts to do so will result in a compile-time error.
Next, let’s explore the usage of the final keyword in Java with methods. When a final method is declared, it cannot be overridden by a subclass. This is useful when we want to ensure that the implementation of a method in a superclass remains unchanged in any subclasses. Here’s an example:
public class Vehicle { public final void maxSpeed() { System.out.println("The maximum speed is 200 km/h."); } } public class Car extends Vehicle { // This override will result in a compile-time error // because the maxSpeed() method in the Vehicle class is final. @Override public void maxSpeed() { System.out.println("The maximum speed is 250 km/h."); } }
In the above example, the Car class attempts to override the maxSpeed() Java final method, declared in the Vehicle superclass. This will lead to a compile-time error as the final keyword prevents the method from being overridden.
Lastly, let’s discuss using the final keyword in Java with classes. A class declared using the final keyword cannot be extended. This is useful to prevent a class from being a superclass to any other class. For example:
public final class ImmutableClass { // class implementation } // This class definition will result in a compile-time error // because the ImmutableClass is declared as final. public class MutableClass extends ImmutableClass { // class implementation }
As shown above, the MutableClass attempts to extend the ImmutableClass, declared final. This will cause a compile-time error because the final keyword prevents the ImmutableClass from being extended.
3. Java Final Variables
Let’s discuss in detail how to create Java final variable. We will cover two sub-sections: Primitive Data Types and Reference Variables.
3.1. Primitive Data Types
When using the Java final keyword with primitive data types (such as float, int, char, etc.), the variable’s value cannot be changed once it has been initialized. This is particularly useful when declaring constants or values that should not be modified. Consider the following example:
final int MAX_VALUE = 100; // MAX_VALUE = 200; // This would result in a compiler error.
As you can see, the primitive data type’s final variable ensures its value remains constant throughout the program’s life.
3.2. Final Reference Variable
Creating final reference variables, such as objects or arrays, ensures that the reference cannot be changed once initialized. However, the properties or elements of the object or array can still be modified. Here’s an example:
final List myList = new ArrayList<>(); myList.add("Hello"); // Allowed, modifying the object, not reference. // myList = new ArrayList<>(); // Results in a compiler error.
The above example shows that defining the final reference variable prevents reassigning the object reference to a new object. However, the object’s contents can still be modified.
It is important to remember that protecting the object’s properties or elements from being modified may require additional steps, such as making the properties individually final or using immutable data structures.
4. Final Methods
When working with Java, it’s common to encounter situations where we want to restrict or control the behaviour of our methods. One useful way to achieve this is to define the final method. This helps protect our implementation from being unintentionally or undesirably overridden in subclasses.
Creating the final method means that subclasses cannot override the method. This is particularly useful when we have an implementation that must not change and is critical to maintaining a consistent state throughout the application. Let’s see an example:
public class Vehicle { public final void startEngine() { // Implementation here } } class Car extends Vehicle { // This will produce a compile-time error because // startEngine is marked as final in the parent class. public void startEngine() { // Attempt to override startEngine } }
In the code above, we have a parent class named Vehicle with a startEngine() final method. When we create a subclass called Car and attempt to override the startEngine() method, we receive a compile-time error.
It’s essential to note that creating the final method does not affect its behaviour or impact callers; it restricts the method from being overridden in subclasses. The choice to use the final keyword in Java comes down to individual preference and the specific use cases of methods within your application.
When designing methods and classes, consider whether the implementation must remain consistent and unchangeable within subclasses. Using the final keyword can be a helpful tool in establishing design constraints and promoting a stable and predictable application structure.
5. Final Classes
A class can be marked as final using the following syntax:
public final class ExampleClass { // Class contents }
By marking a class as final, we prevent it from being extended by any other class. This essentially means that no class can inherit from a Java final class. This can be useful if we want to prevent misuse or ensure the encapsulation of our class. For instance, if our class implements a specific algorithm or behaviour that should remain untouched or contain sensitive data, marking it as final ensures its integrity.
Consider the following example:
public final class SensitiveData { private String secret; public SensitiveData(String secret) { this.secret = secret; } public String getSecret() { return secret; } }
In this example, by marking the SensitiveData class as final, we can ensure that the secret is not accessed or modified by any subclass, maintaining the security of our data.
Using the Java final keyword with classes is an effective strategy to maintain the integrity and encapsulation of our code, especially when dealing with sensitive data or unchangeable behaviours. However, it is crucial to handle such a design decision wisely and consider its potential impact on the flexibility and extensibility of our code.
6. Benefits of the Java Final Keyword
There are several benefits when using the final Keyword in Java. This section will explore how it prevents modifications, ensures immutability, and optimizes performance.
6.1. Preventing Modifications
By declaring a class, attribute, or final method, we make it non-changeable. This means that a final class cannot be extended, a final attribute will always have the same value, and a final method cannot be overridden.
6.2. Immutability
Immutability is a valuable aspect of programming, ensuring that an object’s state cannot be altered after its creation. By marking a class and its attributes as final, we can create an immutable object, enhancing code readability and reducing the likelihood of bugs.
6.3. Performance Optimization
Using the final keyword in Java can improve performance by allowing the compiler to optimize the code more effectively. Since variables, methods, or classes cannot be changed when defined with the final keyword, the compiler can make better decisions about inlining variables or method calls and reduce the time spent in lookups. Here’s an example that illustrates the performance benefits:
public class PerformanceTest { public final int optimizedValue = 42; public final int calculateSquare() { return optimizedValue * optimizedValue; } }
In this case, the compiler can inline the calculateSquare final method, which means replacing method calls with the actual method code, thereby reducing the overhead of method calls and improving the execution speed.
7. Common Use Cases of Final Keyword
In Java, using the final keyword in method parameters is possible. By using the final keyword with method parameters, we can prevent them from being modified inside the method. This can be useful to ensure that the parameter value remains unchanged throughout the method execution.
public void exampleMethod(final int a, final String b) { // a = 10; // This would cause a compile-time error. // b = "New String"; // This would also cause a compile-time error. }
Although this usage is not as common, it can be helpful in some situations where parameter modifications might lead to unexpected behaviour or bugs.
Anonymous Inner Classes
One more common use case for the final keyword in Java is in anonymous inner classes. When working with anonymous inner classes, we often need to access local variables from the enclosing method. To do that, the local variables should be either final or effectively final (not modified after initializing). This ensures that the variable’s value does not change after creating the anonymous inner class instance.
public void exampleInnerClass() { final int outerVariable = 42; new Thread(new Runnable() { public void run() { System.out.println("Outer variable: " + outerVariable); } }).start(); }
5. Summary
In this article, we explored the importance and usage of the final keyword in Java. Utilizing final variables, methods, and classes, we can create constant values, prevent methods from being overridden, and stop classes from being extended.
Using the final keyword appropriately in our Java programs allows us to establish a solid foundation for building reliable, efficient, and maintainable code. It also helps convey our intentions clearly to other developers working with or maintaining our code in the future.
Daniel Barczak
Daniel Barczak is a software developer with a solid 9-year track record in the industry. Outside the office, Daniel is passionate about home automation. He dedicates his free time to tinkering with the latest smart home technologies and engaging in DIY projects that enhance and automate the functionality of living spaces, reflecting his enthusiasm and passion for smart home solutions.
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