The final keyword in Java is a modifier that allows developers to prevent further modification of variables, methods, and classes. It serves a variety of purposes, from preventing accidental changes to important data to improving performance through the use of polymorphism. Additionally, the use of finalcan also aid in creating thread-safe classes and methods.
When deciding to use the final keyword, it’s important to consider the intended use case. For example, if you want to prevent a variable from being modified, you would declare it as final. Similarly, if you want to prevent a method from being overridden, you would declare it as final. And, if you want to prevent a class from being subclassed, you would declare it as final.
It’s also worth noting that while final can offer several benefits, it also has its drawbacks. For instance, declaring a variable as final can make it more difficult to change its value later on, and declaring a class as final can prevent it from being extended in the future. However, when used correctly, the final keyword can greatly improve the security and maintainability of your code.
What is final Keyword in Java
The final keyword in Java is a tool that indicates that a particular variable, method, or class cannot be modified. This means that a final variable cannot be reassigned, a final method cannot be overridden, and a final class cannot be extended. The final keyword is used to improve security and performance, as well as to create immutable objects and thread-safe classes.
For example, when you declare a variable as final, you can ensure that its value remains constant and cannot be changed. This can be useful for important data that should not be accidentally modified. Similarly, when you declare a method as final, you can prevent it from being overridden by subclasses and ensure that its behavior remains consistent. And when you declare a class as final, you can prevent it from being extended, which can be useful for utility classes and other special cases.
It’s important to note that you can also use the final keyword in combination with other Java features such as the private keyword and encapsulation to improve the security and maintainability of an application. This makes the final keyword a versatile and powerful tool for Java developers.
final Variables in Java
How to Declare a Variable as final
Declaring a variable as final in Java is simple. All you have to do is to add the final keyword before the variable’s data type. For example, the following line of code declares x as a final integer variable with a value of 5:
final int x = 5; final double y = 3.14; final String name = "John";
It’s also possible to declare a final variable without initializing it, but it must be initialized before the constructor ends, otherwise, the compiler will raise an error.
final int x;
public MyClass(){
x = 5;
}
Final variables can be used to improve the security of an application by preventing the accidental or intentional modification of important data. For instance, if you have a final variable that stores a password, you can ensure that the password cannot be changed, even by mistake. Also, you can use final variables to protect the state of an object from being modified by external code.
It’s important to note that there are common pitfalls and best practices when using final variables. For example, you should always properly initialize final variables, either in the declaration or in a constructor. Additionally, it’s important to understand the difference between final variables and constant variables, which are defined using the static final keyword and are usually written in all uppercase. Another best practice is to use final variables only when necessary, because it can make your code less flexible and harder to maintain.
Differences between final instance variables and final static variables
Final instance variables are specific to a particular object and belong to that object. For instance, if you create two objects of the same class, each object will have its own copy of the final instance variable. On the other hand, final static variables are shared by all objects of a class and belong to the class itself, which means that all the objects of the class share the same copy of the final static variable.
final Method in Java
How to Declare final Methods in Java
To declare a method as final, simply add the final keyword before the method’s return type, the method name, and the parameter list. For example, the following code declares a final method called MyMethod that takes no parameter and returns nothing:
final void myMethod(){
// method body
}
It’s also possible to declare a final method with parameters, such as the following example:
final int myMethod2(int a, int b){
return a+b;
}
Benefits and Drawbacks of final Methods in Java
Final methods offer some benefits such as preventing the method from being overridden by subclasses. This ensures the consistency of the method’s behavior, and it’s particularly useful when you want to prevent a subclass from changing the behavior of a method that should always behave in a specific way. Additionally, final methods can also improve security by preventing external code from modifying the behavior of the method, which can be important in cases where the method is used to handle sensitive data or perform critical operations.
However, declaring a method as final can also limit the flexibility of your code, because it cannot be overridden or extended. This can make it harder to extend the functionality of a class, or to write code that can work with a variety of different classes.
Final methods can be used in combination with polymorphism to improve performance by allowing the Java Virtual Machine (JVM) to perform method invocation at compile-time rather than runtime. This is called “invocation inlining”, and it can significantly increase the performance of your code by reducing the number of method calls.
When a final method is called, the JVM can replace the call with the actual code of the method, which eliminates the overhead of method invocation, and this results in faster execution time. However, this technique should be used with caution, because it can make your code less maintainable and more prone to errors, since the inlined code can be harder to understand, and it can make debugging more difficult.
It’s also important to note that the JVM may not always inline final methods, even if they are marked as such, because it depends on the JVM’s optimization settings and the complexity of the method.
Therefore, it’s not always guaranteed that final methods will result in improved performance, and it’s important to test and measure the performance of your code before relying on this technique. It’s also important to balance the potential performance gains with the maintainability and readability of your code, and to only use final methods when it’s necessary and beneficial for your specific use case.
final Classes in Java
To declare a class as final in Java, you simply add the final keyword before the class name. For example:
final class MyClass {
// class code here
}
An example of a final class is the String class in Java:
final class String {
// class code here
}
As String is a final class, it cannot be extended or subclassed. This ensures that the String class remains consistent and its behavior cannot be changed by subclasses, and also JVM can perform certain optimizations on final classes like inlining the methods.
Declaring a class as final has several benefits. One of the main benefits is that it prevents the class from being extended or subclassed. This means that no other class can inherit from it, and it cannot be used as a superclass. This can be useful in several scenarios, such as:
- Utility classes: A class designed to perform a specific function, such as a mathematical calculation or a date conversion, is often best left as a
finalclass. This ensures that the class’s behavior remains consistent and cannot be changed by subclasses. - Security:
Finalclasses are often used as part of a security strategy. By making a class final, you can prevent malicious code from subclassing it and potentially gaining access to sensitive data or methods. - Performance: The JVM can perform certain optimizations on
finalclasses. For example, when a method isfinal, the JVM knows it cannot be overridden, so it can inline the method for better performance.
On the other hand, there are also drawbacks to using final classes. For example, it can make your code less flexible and limit the ability to reuse or extend existing classes. If a class is final , you cannot use it as a superclass for other classes, which can make it harder to share functionality between classes. Additionally, it can be difficult to test final classes, since they cannot be overridden. Therefore, it’s important to carefully consider when and why you want to use final classes in your code.
It’s important to note that final classes can be used in combination with other Java features such as the private keyword and encapsulation to improve the security and maintainability of an application. It’s also a good idea to use final classes when creating utility classes that should not be subclassed, to prevent unintended behavior.
Using final Keyword with Inheritance in Java
The final keyword in Java affects inheritance by preventing a class or method from being overridden or subclassed. For example, when you declare a class as final , any attempt to extend it will result in a compilation error. Similarly, when you declare a method as final, any attempt to override it in a subclass will also result in a compilation error.
Using final in this way can be useful in several scenarios such as:
- Preventing unintended behavior: Declaring a class or method as
finalcan prevent unintended behavior caused by subclasses. For example, if you have a class that performs a specific function, you may want to prevent any subclasses from modifying its behavior. - Improving security: By making a class or method
final, you can prevent malicious code from subclassing it and potentially gaining access to sensitive data or methods.
Additionally, the use of final can also be used to create immutable classes and objects. An immutable class is one whose state cannot be modified after it is created. This can be useful for improving thread safety, as well as for creating objects that will always have the same state.
Creating immutable classes has several benefits, such as:
- Thread safety: Immutable classes are thread-safe because their state cannot be modified, so there is no need for synchronization.
- Simplifying code: Immutable classes are simpler to reason about than mutable classes, because their state cannot change.
However, there are also drawbacks to creating immutable classes, such as:
- Increased memory usage: Immutable classes can use more memory than mutable classes, because a new object must be created each time the state changes.
- Limited flexibility: Immutable classes are less flexible than mutable classes, because their state cannot be modified.
Here are some examples of how the final keyword can be used with inheritance in Java:
1. Preventing a class from being subclassed
final class MyClass {
// class code here
}
// This will result in a compilation error
class MySubclass extends MyClass {
// class code here
}
2. Preventing a method from being overridden
class MyClass {
final void myMethod() {
// method code here
}
}
class MySubclass extends MyClass {
// This will result in a compilation error
void myMethod() {
// method code here
}
}
3. Creating an immutable class
final class MyImmutableClass {
private final int myField;
public MyImmutableClass(int myField) {
this.myField = myField;
}
public int getMyField() {
return myField;
}
}
In the above example, once an instance of MyImmutableClass is created, its myField variable cannot be modified, making the class immutable.
4. Creating an immutable object
class MyImmutableClass {
private final MyMutableClass myMutableObject;
public MyImmutableClass(int myField) {
this.myMutableObject = new MyMutableClass(myField);
}
public int getMyField() {
return myMutableObject.getMyField();
}
public MyImmutableClass withMyField(int myField) {
return new MyImmutableClass(myField);
}
}
In the above example, MyImmutableClass holds a reference to an instance of MyMutableClass, but it does not expose any setters to modify its state. Instead, it provides a method withMyField that creates a new instance of MyImmutableClass with the desired value, making the object immutable.
It’s important to note that while the use of final can be used to create immutable classes and objects, it’s not the only way to do so. Other techniques such as using private final fields and returning new objects can also be used to create immutable classes.
Difference between final, finally and finalize
In Java, the keywords “final, finally and finalize have distinct meanings and uses.
Final is used to indicate that a particular variable, method, or class cannot be modified. This means that a final variable cannot be reassigned, a finalmethod cannot be overridden and a finalclass cannot be subclassed. This can be useful for preventing unintended behavior, improving security, and creating immutable classes and objects.
Finally is used in exception handling. It is used in a try-catch block to specify a block of code that will always be executed regardless of whether an exception is thrown or not. For example, if you open a file in a try block and an exception is thrown when trying to read from it, the finally block can be used to close the file, ensuring that the resources are cleaned up properly.
Finalize is a method that is called by the garbage collector before an object is garbage collected. It is used to perform any final cleanup before the object is destroyed. However, it’s important to note that the garbage collector is not guaranteed to call the finalize method, so it’s not recommended to use this method for critical tasks.
To sum up,
finalis used to make variables, methods and classes non-modifiablefinallyis used in exception handling to ensure that certain code runs after try-catch blockfinalizeis a method called by garbage collector to perform cleanup before an object is destroyed. It’s important to note that these three keywords have distinct uses and should not be confused with one another.
Conclusion
In conclusion, the final keyword in Java is a powerful tool that allows developers to indicate that a particular variable, method, or class cannot be modified. This means that a final variable cannot be reassigned, a final method cannot be overridden and a final class cannot be subclassed. The use of final can be used for various purposes, such as preventing unintended behavior, improving security, and creating immutable classes and objects.
When using final , it’s important to keep in mind that it can limit the flexibility and reusability of code. However, when used correctly, it can help improve the security and performance of your application. It can also be used in conjunction with other Java features such as the “private” keyword and encapsulation to further improve the security and maintainability of the application.
In summary, the final keyword is a powerful feature in Java, which can be used to make your code more secure and maintainable, but it’s important to use it wisely and with a clear purpose in mind. With the knowledge of final keyword and its implications, you can make better decisions about when and how to use it in your code.
