06 static, final keywords

• 1. Static Keyword
  • [[#1. Static Keyword#Definition|Definition]]
  • [[#1. Static Keyword#Characteristics|Characteristics]]
  • [[#1. Static Keyword#Usage|Usage]]
  • [[#1. Static Keyword#Example|Example]]
• 2. Final Keyword
  • [[#2. Final Keyword#Definition|Definition]]
  • [[#2. Final Keyword#Characteristics|Characteristics]]
  • [[#2. Final Keyword#Usage|Usage]]
  • [[#2. Final Keyword#Example|Example]]

In Java, the static and final keywords are used to define the behavior of variables, methods, and classes. Here’s a detailed overview of both keywords, including definitions, characteristics, examples, and use cases.

1. Static Keyword

Definition

The static keyword is used to indicate that a particular member (variable or method) belongs to the class itself rather than to instances of the class. This means that a static member can be accessed without creating an instance of the class.

Characteristics

• Class-level Access: Static members belong to the class and can be accessed directly using the class name.
• Single Instance: There is only one copy of a static member, regardless of how many instances of the class exist.
• Memory Management: Static variables are stored in the static memory, making them accessible even when no instances of the class exist.

Usage

• Static Variables: Often used for constants or shared resources.
• Static Methods: Used for utility functions that do not depend on instance variables.

Example

public class StaticExample {
    static int staticCounter = 0; // Static variable
 
    public StaticExample() {
        staticCounter++; // Increment the static variable for each instance
    }
 
    static void displayCounter() { // Static method
        System.out.println("Static counter: " + staticCounter);
    }
 
    public static void main(String[] args) {
        StaticExample obj1 = new StaticExample();
        StaticExample obj2 = new StaticExample();
        
        StaticExample.displayCounter(); // Outputs: Static counter: 2
    }
}

2. Final Keyword

Definition

The final keyword is used to declare constants. When a variable, method, or class is declared as final, it cannot be changed, overridden, or inherited.

Characteristics

• Final Variables: Once assigned, their values cannot be changed (immutable).
• Final Methods: Cannot be overridden by subclasses.
• Final Classes: Cannot be subclassed or extended.

Usage

• Final Variables: Used for constants that should not be changed.
• Final Methods: Used to prevent method overriding.
• Final Classes: Used to prevent inheritance.

Example

public final class FinalClass { // Final class
    final int finalValue; // Final variable
 
    public FinalClass(int value) {
        this.finalValue = value; // Initialize final variable
    }
 
    final void displayValue() { // Final method
        System.out.println("Final value: " + finalValue);
    }
}
 
// Cannot subclass FinalClass
// class SubClass extends FinalClass {} // This would cause a compile-time error
 
public class Main {
    public static void main(String[] args) {
        FinalClass obj = new FinalClass(100);
        obj.displayValue(); // Outputs: Final value: 100
    }
}