To build good software, you need to follow certain heuristics. While the heuristics are not always true, there are certain software principles that can help you create good software. In this article, we will discuss 8 principles of software engineering that govern the software development process. To make you understand in a better manner, we will also use code examples to describe the software engineering principles.
The DRY Principle in Software Engineering
The DRY (Don’t Repeat Yourself) principle is a software engineering principle that aims to reduce code duplication and increase maintainability. It does so by ensuring that the same logic or data is not repeated in multiple places. The idea for the DRY principle is that every piece of knowledge in the system should have a single, unambiguous, authoritative representation.
Code duplication leads to a number of problems, such as increased complexity, reduced maintainability, and increased likelihood of bugs. When we repeat the same logic or data in multiple places, it becomes harder to understand, modify, and test the code. If we want to make any changes to the code. duplicated code needs to be modified in multiple places. This increases the chances of errors and makes it more difficult to verify that the changes have been made correctly.
To follow the DRY principle, you should aim to create a single, reusable implementation of any given logic or data. For this, you can create reusable functions, classes, or modules, by using inheritance or composition to share code, by creating common libraries, or by using design patterns.
In practice, You can implement the DRY principle in software engineering by using the following measures.
- Identify and eliminate duplicate code by creating reusable functions and classes.
- Use inheritance, composition, common libraries, and design patterns.
- Create clear and well-defined interfaces.
- Use clear and meaningful names for variables and functions.
- Separate the concerns and keep the codebase modular. i.e. Increase cohesion and reduce coupling in your code.
By following the DRY principle, you can create more maintainable and less error-prone code.
To understand the DRY principle in a better manner, consider the following example.
class Employee:
def __init__(self, name, age, salary):
self.name = name
self.age = age
self.salary = salary
def calculate_bonus(self):
if self.age > 40:
return self.salary * 0.1
else:
return self.salary * 0.05
class Manager(Employee):
def calculate_bonus(self):
if self.age > 50:
return self.salary * 0.15
else:
return self.salary * 0.1
In the above example, the calculate_bonus method is duplicated in both the Employee and Manager classes. This violates the DRY principle. If the bonus calculation changes, it must be updated in both places. We can move the bonus calculation logic to a separate class to implement the DRY principle.
For instance, consider the following code.
class BonusCalculator:
def calculate(self, employee):
if type(employee)==”Employee”:
if employee.age > 40:
return employee.salary * 0.1
else:
return employee.salary * 0.05
Elif type(employee)==”Manager”:
if employee.age > 50:
return employee.salary * 0.15
else:
return employee.salary * 0.1
class Employee:
def __init__(self, name, age, salary):
self.name = name
self.age = age
self.salary = salary
self.bonus_calculator = BonusCalculator()
def calculate_bonus(self):
return self.bonus_calculator.calculate(self)
class Manager(Employee):
def __init__(self, name, age, salary):
super().__init__(name, age, salary)
self.bonus_calculator = BonusCalculator()
In the above code, the bonus calculation logic is moved to the BonusCalculator class. Then we use the code in both the Employee and Manager classes. This makes the code more maintainable, as any changes to the bonus calculation logic only need to be made in one place, which is the BonusCalculator class. Also, if a new type of employee is added, for example, a SeniorManager, it can use the BonusCalculator class and can make necessary changes.
The KISS Principle in Software Engineering
The KISS (Keep It Simple, Stupid) principle is a software engineering principle that encourages keeping software designs simple and easy to understand. The idea behind the KISS principle is that simple designs are easier to understand, maintain, and modify than complex designs. This principle encourages you to avoid unnecessary complexity and to prioritize simplicity in your code and designs. For this, you can break down complex problems into smaller, simpler parts that can be easily understood and solved.
The KISS principle promotes the use of simple, straightforward solutions rather than convoluted or overly complex ones. Simple code is typically easier to read, understand, and maintain, which leads to fewer bugs and faster development times. It also makes it easier for new developers to understand the codebase and contribute to the project.
In practice, the KISS principle can be implemented using the following tasks.
- Write code that is easy to read, understand and test.
- Use simple data structures and algorithms.
- Avoid unnecessary abstractions.
- Reduce the number of dependencies.
- Remove duplicate code.
- Use clear and meaningful names for variables and functions.
- Keep the overall design of the code simple.
To understand the KISS principle in a better way, consider the following example.
# Violating KISS principle
def create_message(name, age, gender, occupation):
message = "Hello, my name is " + name + " and I am " + str(age) + " years old. "
if gender.lower() == "male":
message += "I am a " + occupation + "."
elif gender.lower() == "female":
message += "I am a " + occupation + "."
else:
message += "My gender is not specified and I am a " + occupation + "."
return message
# Following KISS principle
def create_message(name, age, occupation):
message = f"Hello, my name is {name} and I am {age} years old. I am a {occupation}."
return messageIn the above code, the first function violates the KISS principle. It has multiple conditions and string concatenation to form the message. It’s harder to understand and test. In contrast, the second function follows the KISS principle by using string formatting to create the message, which is more readable, understandable, and testable.
By following the KISS principle, you can design software that is easy to understand, maintain, and modify. This can save development time, reduce bugs, and improve the overall quality of the software.
Suggested reading: C# vs Java: Performance, Syntax, Advantages, and Disadvantages
The SOLID Principles of Software Engineering
SOLID is an acronym used for the five principles of object-oriented programming and design. These principles were first introduced by Robert C. Martin and are widely used as a guide for creating maintainable and scalable software. The SOLID principles of software engineering are as follows.
- Single Responsibility Principle (SRP)
- Open-Closed Principle (OCP)
- Liskov Substitution Principle (LSP)
- Interface Segregation Principle (ISP)
- Dependency Inversion Principle (DIP)
Single Responsibility Principle (SRP)
The single responsibility principle states that a class or module should have one and only one reason to change. This principle encourages the separation of concerns and promotes the creation of small, focused classes that have a single responsibility.
To understand this, consider the following example.
class Account:
def __init__(self, account_number, account_holder):
self.account_number = account_number
self.account_holder = account_holder
self.balance = 0
def deposit(self, amount):
self.balance += amount
def withdraw(self, amount):
self.balance -= amount
In the above example, the Account class has a single responsibility, which is to represent an account and perform operations on it. The class has three attributes: account_number, account_holder, and balance. It also has two methods: deposit() and withdraw(). The deposit() method increases the balance of the account by a given amount, and the withdraw() method decreases the balance of the account by a given amount.
By having only one responsibility, the class is easy to understand, test, and maintain. If a requirement comes in to add new functionality, let’s say adding a method to check the account status, it can be added to a different class.
Open/Closed Principle (OCP)
The open-closed principle states that the classes and modules in a program should be open for extension but closed for modification. This principle encourages the use of abstraction, encapsulation, and polymorphism to create flexible and extensible code.
To understand this, consider the following example.
class Shape:
def area(self):
pass
class Rectangle(Shape):
def __init__(self, width, height):
self.width = width
self.height = height
def area(self):
return self.width * self.height
class Circle(Shape):
def __init__(self, radius):
self.radius = radius
def area(self):
return 3.14 * (self.radius ** 2)
In the above example, the Shape class is an abstraction of different types of shapes. It has a single method area that is not implemented and should be overridden by the subclasses.
The Rectangle and Circle classes are two examples of subclasses that extend the Shape class and provide their own implementation of the area method. The Rectangle class calculates the area of a rectangle using its width and height, and the Circle class calculates the area of a circle using its radius. The advantage of this design is that if a new shape is added, for example, an Ellipse, it can be added as a new subclass of Shape without changing any existing code.
Liskov Substitution Principle (LSP)
The Liskov substitution principle states that the subtypes of a class or data type must be substitutable for their base types. This principle ensures that subclasses maintain the same behavior as their base classes and can be used interchangeably.
To understand this, consider the following code.
class Bird:
def fly(self):
pass
class Sparrow(Bird):
def fly(self):
return "Flying"
class Penguin(Bird):
def fly(self):
return "Cannot Fly"
In the above example, the Bird class is an abstraction of different types of birds. It has a single method fly that should be overridden by the subclasses.
The Sparrow and Penguin classes are two examples of subclasses that extend the Bird class and provide their own implementation of the fly method. The Sparrow class returns “Flying” when the fly method is called, and the Penguin class returns “Cannot Fly” when the fly method is called.
The advantage of this design is that if a new bird is added, for example, an Ostrich, it can be added as a new subclass of Bird without changing any existing code and it will still be substitutable.
Interface Segregation Principle (ISP)
The interface segregation principle in software engineering states that the classes and modules should not be forced to implement interfaces they do not use. This principle encourages you to create small, focused interfaces that are used by only the classes that need them.
For instance, consider the following example.
class Document:
def print(self):
pass
def fax(self):
pass
class PDF(Document):
def print(self):
return "Printing PDF"
class Word(Document):
def print(self):
return "Printing Word"
def fax(self):
return "Faxing Word"
In the above code, the Document class is an abstraction of different types of documents that can be printed or faxed. It has two methods print and fax that should be overridden by the subclasses.
The PDF and Word classes are two examples of subclasses that extend the Document class. The PDF class provides its own implementation of the print method and does not implement the fax method, as it does not need it. The Word class, on the other hand, provides its own implementation of both the print and fax methods.
This design follows the ISP principle because it allows subclasses to only implement the methods they need, which makes the code more maintainable.
Dependency Inversion Principle (DIP)
The dependency inversion principle states that high-level modules should not depend on low-level modules; both should depend on abstractions. This principle encourages the use of dependency injection and inversion of control to create loosely coupled and easily testable code.
To understand this, consider the following example.
class Controller:
def __init__(self, service):
self.service = service
class Service:
def __init__(self, repository):
self.repository = repository
class Repository:
def __init__(self):
passHere, the dependencies are inverted because the high-level module (Controller) depends on the abstraction of the Service class rather than the implementation. The Service class also depends on the abstraction of the Repository class rather than the implementation.
This design allows for more flexibility and maintainability, as it makes it easy to swap out the implementation of the Repository class without affecting the other classes. Additionally, it allows the addition of new functionality or change of the existing functionality of the Repository class independently of the other classes.
Conclusion
In this article, we have discussed 8 principles of software engineering. To explain the software engineering principles, we have also used code examples.
To learn more about coding, you can read this article on best coding practices. You might also like this article on the advantages of being a programmer.
I hope you enjoyed reading this article. Stay tuned for more informative articles.
Happy Learning!
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