Introduction

In software engineering, inheritance is a well-known principle used to create new classes by inheriting features from existing ones. However, inheritance can lead to problems such as tight coupling, brittleness, and an overly complex class hierarchy. A better alternative is composition, which allows for a more flexible, maintainable, and scalable design. In this blog post, we’ll explore the benefits of composition over inheritance, and provide examples of how you can apply it to your own code.

Inheritance vs Composition

Inheritance is the process by which one class is derived from another class. This means that the derived class inherits all the properties and methods of the parent class, and can also add its own properties and methods. While inheritance can be useful in certain cases, it can also lead to problems such as tight coupling, where changes to one class affect many other classes in the hierarchy. In addition, inheritance can lead to an overly complex class hierarchy, which can make it difficult to maintain and extend the code over time.

Composition, on the other hand, is the process of building complex objects by combining simpler objects or components. This means that a class can be composed of one or more objects, each of which has its own properties and methods. By using composition, you can create a more flexible and modular design, where each component can be modified or replaced without affecting other components.

Example of Composition

Let’s take a look at an example of composition in action. Suppose we have a program that manages employee data, and we want to create a class that calculates the total salary of a team of employees. We could create a new class called SalaryCalculator that extends the Employee class:

class SalaryCalculator extends Employee {
    public int calculateTotalSalary() {
        int totalSalary = 0;
        for (Employee employee : employees) {
            totalSalary += employee.getSalary();
        }
        return totalSalary;
    }
}

While this approach might work, it creates tight coupling between the SalaryCalculator and Employee classes. If we need to modify the Employee class, we might also need to modify the SalaryCalculator class.

A better approach is to use composition, and create a new class called Team that contains a list of Employee objects:

class Team {
    private List<Employee> employees;
    
    public Team(List<Employee> employees) {
        this.employees = employees;
    }
    
    public int calculateTotalSalary() {
        int totalSalary = 0;
        for (Employee employee : employees) {
            totalSalary += employee.getSalary();
        }
        return totalSalary;
    }
}

By using composition, we have created a more flexible design that can be modified or extended without affecting the other classes in the hierarchy. For example, if we need to add a new Employee class, we can do so without modifying the Team or SalaryCalculator classes.

Conclusion

In conclusion, composition is a powerful technique that can help you create more flexible, maintainable, and scalable software designs. By using composition, you can avoid the problems of tight coupling and an overly complex class hierarchy that can arise from inheritance. While it can be challenging to apply this principle at first, it can lead to code that is easier to maintain, extend, and understand over time.