Class Method, Static Method, and Instance Method: Understanding Their Differences and Benefits
Have you ever wondered what class method, static method, and instance method are all about? These are some of the essential programming concepts you’ll encounter in most object-oriented programming languages like Python and Java.
Understanding the differences between these methods, their primary uses, and the best time to use them can help you become a more efficient programmer. In this article, we’ll discuss class, static, and instance methods, their differences, and when to use them.
Instance Method
Instance methods are methods that are bound to any object instance of a class. In simple terms, these are methods that exist only in an instance of a class, and their results only apply to that specific instance.
The primary keyword(s) associated with instance methods include instance variables and instance methods. Here’s an example of an instance method in Python:
class Rectangle:
def __init__(self, width, height):
self.width = width
self.height = height
def get_area(self):
return self.width * self.height
r = Rectangle(10, 5)
print(r.get_area())
In this example, get_area is an instance method that returns the area of a rectangle object.
We create a rectangle object with a width of 10 and a height of 5. The get_area method is invoked on the r rectangle object, which returns 50.
Class Method
A class method is a method that operates on the class level rather than an instance level. In other words, class methods are bound to a class, not an instance of it.
The primary keyword(s) associated with class methods include class variables, class method, and factory method. Here’s an example of a class method in Python:
class Employee:
num_of_employees = 0
def __init__(self, name, salary):
self.name = name
self.salary = salary
Employee.num_of_employees += 1
@classmethod
def from_string(cls, emp_str):
name, salary = emp_str.split('-')
return cls(name, salary)
e = Employee.from_string('John Adams-50000')
In this example, we define a class method from_string that takes a string and creates a new employee object based on the string.
The cls keyword represents the class. We use it to create a new instance of the class.
We call the from_string class method using the Employee class rather than an instance of it.
Static Method
A static method is a method that’s bound to the class and not the instance of the class. Static methods are not associated with the class or instance state; they perform tasks that have no relation to instance or class state.
The primary keyword(s) associated with static methods include utility method, instance variables, and class variables. Here’s an example of a static method in Python:
class MathUtils:
@staticmethod
def add(a, b):
return a + b
print(MathUtils.add(2, 3))
In this example, we define a static method add that takes two arguments a and b.
The method returns the sum of the arguments passed to it. Notice that there’s no need to create an instance of the class to use the add static method.
Differences between Class Method, Static Method, and Instance Method
Primary Use of Class Method
Class methods operate on the class level, making them ideal for accessing or modifying class state or modifying class variables. You should use a class method when you want to modify a class variable that holds common data across all instances of the class or when you want to modify the class state.
Primary Use of Instance Method
Instance methods operate on an object instance, making them ideal for modifying object state. You should use instance methods when you need to change the value of instance variables.
Primary Use of Static Method
Static methods have limited use and are ideal for performing utility or data conversion tasks that do not depend on instance or class state. You should use a static method when you need to perform a task that has no relation to instance or class state.
Method Definition
To define a class method, you can use the classmethod decorator. To define a static method, you can use the staticmethod decorator.
You do not need any decorator to define an instance method.
Method Call
To call a class method or a static method, you can call it using the class name. To call an instance method, you can only call it using an instance of the class.
Attribute Access
You can access both class and instance attributes in instance methods. However, in class methods, you can only access class attributes and not instance attributes.
In static methods, you cannot access class or instance attributes because they are independent of both.
Class Bound and Instance Bound
Instance methods are bound to an object instance, which means they only operate on that specific instance. Unlike instance methods, class methods and static methods are bound to the class and are not associated with any instance.
To access class methods and static methods, you can use the class name or an instance of the class.
Conclusion
In conclusion, knowing the differences between class method, static method, and instance method is essential for writing better and more efficient object-oriented programs. Class methods perform tasks on the class level, while instance methods operate on object instances.
On the other hand, static methods are independent of both class and instance. This basic understanding of these methods and their primary uses can help you write better and more powerful programs.
Memory Consumption of Instance and Static Methods
When choosing between instance and static methods, another important consideration lies in the memory consumption of the program. Instance methods and static methods consume memory differently due to the way they are stored in the program’s memory.
Instance Methods and Memory Consumption
When you define an instance method in a class, each time you create a new instance of that class, the method is duplicated, and a new copy is created for each instance. This means that if you have many instances of the class, the memory consumption of the program will increase as each instance will have its unique copy of the method.
For instance, suppose that we define a simple class that has an instance method:
class Dog:
def bark(self):
print("Woof!")
When we create an instance of this class, the bark method is duplicated, and a new copy is created for the instance. If we create several instances of the Dog class, each instance will have its own copy of the bark method, leading to an increase in memory consumption.
first_dog = Dog()
second_dog = Dog()
print(first_dog.bark is second_dog.bark) # False
The output of the above code will be False since each instance has a unique method. The memory consumption of instance methods can become more significant if the methods are complex and perform many operations, as each copy needs memory to store the code and any variables that they use.
Static Methods and Memory Consumption
In contrast to instance methods, when you define a static method in a class, only one copy of the method is created for the class, regardless of how many instances of the class are created. This means that the memory consumption of the program will remain constant, regardless of the number of instances created.
For instance, suppose we define a class with a static method:
class Shape:
@staticmethod
def get_area(length, width):
return length * width
In this example, the get_area method is defined as a static method. When we create instances of the Shape class, the get_area method remains the same for all instances since it is a static method.
This means that, unlike with instance methods, the memory consumption of the program doesn’t increase with each instance created.
first_shape = Shape()
second_shape = Shape()
print(first_shape.get_area is second_shape.get_area) # True
The output of the above code will be True since both instances use the same static method.
Static methods are especially useful when we need to define a method that doesn’t modify any state but instead performs a specific task or returns a value. Since static methods do not rely on an instance, they can be used independently and do not contribute to an increase in memory consumption.
Class Methods and Memory Consumption
Class methods work differently from both instance and static methods in terms of memory consumption. Similar to static methods, class methods only have a single copy in memory and are associated with the class, not any particular instance.
However, they can still modify the class state, which can increase memory consumption. For example, suppose we define a class with a class method:
class Car:
num_of_cars = 0
def __init__(self):
Car.num_of_cars += 1
@classmethod
def get_num_of_cars(cls):
return cls.num_of_cars
In this example, the get_num_of_cars method is defined as a class method.
However, it can still modify the num_of_cars class variable and thereby contribute to an increase in memory consumption. Since the num_of_cars variable is shared across all instances of the Car class, all instances can access and modify the variable.
The memory consumption of class methods, therefore, depends on the size and complexity of the class state that they modify. Since class methods can modify the class state, they must be used somewhat sparingly, and the class state should be kept as minimal as possible to avoid any unnecessary increase in memory consumption.
Conclusion
When writing object-oriented programs, it’s crucial to consider the memory consumption of instance, static, and class methods. Instance methods tend to increase memory consumption as each instance has a unique copy of the method, while static methods have a constant memory consumption since there is only one copy for the entire class.
Class methods are similar to static methods but can modify the class state leading to an increase in memory consumption. By understanding how these methods impact memory consumption, you can make informed decisions when choosing between them to create more efficient and optimized programs.
In this article, we have discussed the differences between class method, instance method, and static method in detail. We have seen that instance methods are bound to object instances and consume memory each time a new instance is created, while static methods and class methods have constant memory consumption.
We have also highlighted the primary use cases for each method, how to define and call them, and their attribute access and binding. As developers, understanding the differences between these methods is essential to writing more efficient and optimized object-oriented programs.
By considering memory consumption and the methods’ primary uses, we can make informed decisions when choosing which method to use and create more powerful and streamlined programs.