Programming Fundamentals › Object-Oriented Programming

Static Member

A field or method that belongs to the class rather than an instance.

Also known as: static method, static field, class method, class variable

A static member is a field or method that belongs to the class itself, not to any one object. You use it through the class name, without creating an instance.

class MathUtil {
    static final double TAX = 0.2;                       // static field (a constant)
    static int square(int n) { return n * n; }           // static method
}

MathUtil.square(5);       // 25, no object needed

class Temperature:
    @staticmethod
    def c_to_f(c):                    # no self: it doesn't use an object
        return c * 9 / 5 + 32

    @classmethod
    def from_kelvin(cls, k):          # receives the class; handy as an alternative constructor
        return cls(k - 273.15)

class Id { static next = 1; static generate() { return Id.next++; } }

Static vs instance

When to use

• Utility functions that don’t depend on object state.
• Constants shared by all instances.
• Factory methods (User.from_json(...)).

Cautions

• Shared mutable static state is a global variable in disguise: hard to test and unsafe across threads or requests.
• Hard to replace in tests. Code that calls static methods directly can’t easily be swapped for a fake.
• Overuse turns a class into a bag of functions. A plain module may be clearer.