What are static variables?

Static variables belong to the class, not to a specific instance. They exist as a single instance throughout the entire runtime of the program and are shared among all objects of that class. Changing a static variable by one object will be visible to other objects.

Main characteristics:

• Belonging: To the class.
• Number of instances: One per class.
• Lifetime: From the moment the class is loaded until the program terminates.
• Access: Usually by the class name ClassName.staticVariable, although access through an instance is also possible (not recommended).
• Initialization: Once when the class is loaded.

Examples of usage:

• Counters of created class objects.
• Constants shared across the entire class.
• Shared resources managed by the class.

Example in Java:

class MyClass {
    static int counter = 0; // Static variable

    public MyClass() {
        counter++; // Increment static counter upon object creation
    }

    public static void main(String[] args) {
        MyClass obj1 = new MyClass();
        MyClass obj2 = new MyClass();

        System.out.println(MyClass.counter); // Output: 2
    }
}

Example in Python:

class MyClass:
    counter = 0  # Static variable

    def __init__(self):
        MyClass.counter += 1  # Increment static counter

    def main():
        obj1 = MyClass()
        obj2 = MyClass()

        print(MyClass.counter) # Output: 2

    if __name__ == "__main__":
        main()