Key differences between Static in Java and Final in Java

Static in Java

In Java, the keyword static indicates that a particular member (variable, method, or block) belongs to the class, rather than instances of the class. This means that static members are shared among all instances of the class. Static variables are initialized only once, at the start of the execution and reside in the common memory area. This makes them useful for implementing class-level data, such as constants or counters shared by all instances.

Static methods can be called without creating an instance of the class. They can only directly access other static members and can’t access instance variables or methods directly. Static methods are typically utility methods that operate independently of object state. Static blocks, used for static initializations, execute once when the class is loaded.

Functions of Static in Java:

• Shared Variable:

Static variables are shared among all instances of a class, storing a common value rather than individual states for each object.

• Memory Efficiency:

Since static variables are shared, they are created and stored only once in memory, which makes the program more memory efficient when many objects need to access the same data.

• Static Methods:

Static methods belong to the class rather than any object, and can be called without creating an instance of the class. This is useful for utility or helper methods that perform operations independent of object state.

• Singleton Pattern:

Static variables and methods are essential for implementing the Singleton pattern in Java, ensuring that a class has only one instance throughout the application.

• Static Blocks:

Static initialization blocks are executed when the class is loaded by the JVM, before any object instantiation or static method is called. This is useful for complex initialization that might require more than a simple field assignment.

• Constants:

Static final variables are used to create constants. These constants are accessible without object instantiation and are unchangeable once set, providing a secure way to maintain constant values.

• Class-level Accessibility:

Since static methods and variables can be accessed without creating an instance of their class, they provide a global point of access to resources or methods that are logically class-oriented.

• Static Import:

Java allows static members (fields and methods) to be accessed directly (without class reference) through static imports. This can make the code cleaner when repeatedly accessing static members of a particular class.

Example of Static in Java:

Here’s a simple example in Java demonstrating the use of static variables and methods:

public class Calculator {

    // static variable to keep track of the number of calculations

    static int calculationCount;

    // static method to add two numbers

    public static int add(int a, int b) {

        calculationCount++; // Increment the count of calculations

        return a + b;

    }

    // static method to multiply two numbers

    public static int multiply(int a, int b) {

        calculationCount++; // Increment the count of calculations

        return a * b;

    }

    // static method to get the total number of calculations

    public static int getCalculationCount() {

        return calculationCount;

    }

    public static void main(String[] args) {

        // Directly call static methods without creating an instance of Calculator

        int sum = Calculator.add(5, 3);

        int product = Calculator.multiply(4, 2);

        System.out.println(“Sum: ” + sum);

        System.out.println(“Product: ” + product);

        System.out.println(“Total calculations: ” + Calculator.getCalculationCount());

    }

}

Explanation:

• Static Variable:

calculationCount is a static variable. It keeps track of the total number of calculations performed by all methods in the Calculator class. Being static, it is shared across all instances of the class.

• Static Methods:

The methods add, multiply, and getCalculationCount are static. They can be called without creating an instance of the Calculator class. This makes it easier to perform simple operations without needing to manage the state of a specific Calculator object.

• Static Usage:

main method demonstrates how static methods and variables are accessed using the class name rather than through instances. This is typical usage for utility methods that don’t rely on the state of an object.

Final in Java

In Java, the keyword final is used to denote immutability and can be applied to variables, methods, and classes with specific and distinct implications for each. When used with a variable, final makes the variable a constant, meaning its value cannot be modified once it has been assigned. For methods, applying final prevents them from being overridden in subclasses, thereby locking down the method’s implementation in the inheritance hierarchy. When applied to a class, final prevents the class from being subclassed. This is particularly useful for creating immutable classes or ensuring consistent behavior without alteration through inheritance, enhancing security and design clarity. Overall, final helps enforce a contract of behavior that should not be changed by user extensions or misuse.

Functions of Final in Java:

• Prevent Inheritance:

Applying final to a class prevents it from being subclassed. This is useful when a class is not designed to be extended or when an immutable model is required.

• Immutable Variables:

When applied to variables, final ensures that the variable’s value cannot be changed once it is initialized. This is commonly used to define constants.

• Method Locking:

Applying final to methods prevents them from being overridden in subclasses. This is important for methods with critical behavior that must not be altered by inheriting classes.

• Safety in Concurrency:

final variables are safe from change in multi-threaded environments, making them useful in concurrent programming to avoid issues with variable modifications.

• Compiler Optimization:

Since final variables are immutable after assignment, the Java compiler can optimize code more effectively, potentially leading to performance improvements.

• Enforcing Design:

Using final on methods and classes can help enforce certain design constraints and architectural decisions within a software project.

• Use in Anonymous Classes:

Inside anonymous classes, only final or effectively final variables can be accessed from the enclosing scope. This restriction is pivotal for lambda expressions in Java 8 and onward.

• Ensure Consistency:

When an object is passed frequently between different parts of a program, using final on fields or variables helps to ensure that they remain consistent (i.e., their state does not change unexpectedly).

Example of Final in Java:

Here is an example of using the final keyword in Java, demonstrating its application in different contexts such as variables, methods, and classes:

// Final class cannot be subclassed.

final class Constants {

    // Final variable declaration, often used for constants.

    public static final double PI = 3.14159;

    // Final method cannot be overridden.

    public final void showMessage() {

        System.out.println(“This is a final method and cannot be overridden.”);

    }

}

public class Application {

    public static void main(String[] args) {

        // Creating an instance of the Constants class

        Constants constants = new Constants();

        // Accessing the final variable

        System.out.println(“Value of PI: ” + Constants.PI);

        // Calling the final method

        constants.showMessage();

        // The following attempt to extend the final class would result in a compilation error:

        // class ExtendedConstants extends Constants { }

    }

}

Breakdown:

1. Final Class:

Constants class is declared as final, which means it cannot be subclassed. Any attempt to create a subclass of Constants would lead to a compilation error.

2. Final Variable:

PI variable is a constant because it is declared as static final. This combination makes it a constant because it cannot be changed and can be accessed without creating an instance of the class.

3. Final Method:

showMessage() method is declared as final, preventing any subclass (if it were possible to subclass Constants) from overriding this method.

Key differences between Static in Java and Final in Java

Key Similarities between Static in Java and Final in Java

• Both are Keywords:

Static and final are both keywords in Java, used to modify various elements within classes including variables, methods, and classes themselves.

• Compile-Time Handling:

Both static and final attributes are determined at compile-time, meaning that their usage and restrictions are enforced during compilation rather than at runtime.

• Optimization Tools:

Both modifiers can be used to optimize the program. static can reduce memory usage by sharing its fields among all instances, while final can improve efficiency by allowing compilers to make assumptions about the immutability of variables or behavior of methods.

• Access Control:

Each keyword serves as a tool for better defining and controlling access and behavior within classes. static allows for class-wide management without instance-specific data, and final prevents further modification or extension.

• Impact on Inheritance:

Both modifiers influence the inheritance. Static methods can be hidden but not overridden, while final methods can neither be hidden nor overridden. This impacts how subclasses can use and access methods from their superclasses.

• Usage in Class Contexts:

Both can be applied in the context of a class—static can be used to define static blocks, static variables, or static methods, and final can be used to prevent a class from being subclassed.

• Visibility and Utility:

Both modifiers do not inherently affect visibility directly (like private, protected, and public do); however, they modify how elements (variables, methods, classes) can be used or accessed, which plays a crucial role in designing secure and well-organized classes.