Developers are always looking for ways to write better code. One way to achieve this is by following the SOLID principles.
SOLID is an acronym for the five Object-Oriented Design principles developed by Robert C. Martin:
In this article, we'll take a look at how these principles can be applied in Spring Boot development.
The single responsibility principle states that a class should have only one reason to change. In other words, a class should only have one responsibility.
For example, let's say we have a class that handles both database access and business logic. If we need to change the database access code, we'll also need to change the business logic code, even if we don't want to. This violates the single responsibility principle.
A better way to design this would be to create two separate classes, one for database access and one for business logic. This way, we can change the database access code without having to touch the business logic code.
The open-closed principle states that a class should be open for extension but closed for modification. In other words, we should be able to extend a class without having to modify the code of the class.
For example, let's say we have a class that handles customer orders. We may want to add a new feature that allows customers to cancel their orders. If the class is not designed in a way that allows us to add this feature without modifying the existing code, then we violate the open-closed principle.
A better way to design this would be to create an abstract Order class with an abstract cancel() method. Then we can create a concrete CustomerOrder class that extends Order and provides a concrete implementation of the cancel() method. This way, we can add the cancel feature without having to modify the existing code.
The Liskov substitution principle states that a subtype should be substitutable for its supertype. In other words, we should be able to use a subtype in place of its supertype without breaking the code.
For example, let's say we have a class that represents a rectangle. We may want to create a subclass that represents a square. However, if the square class is not designed in a way that it can be used in place of the rectangle class, then we violate the Liskov substitution principle.
A better way to design this would be to make the width and height of the rectangle class invariant. That is, we cannot change the width without also changing the height, and vice versa. This way, the square class can be used in place of the rectangle class without breaking the code.
The interface segregation principle states that a client should not be forced to implement an interface that it doesn't use. In other words, we should not create interfaces with too many methods.
For example, let's say we have an interface that defines methods for processing orders. We may want to create a subclass that only handles customer orders. However, if the interface defines methods for processing both customer and supplier orders, then the subclass will be forced to implement methods that it doesn't use. This violates the interface segregation principle.
A better way to design this would be to create two separate interfaces, one for processing customer orders and one for processing supplier orders. This way, the subclass can implement the interface that it needs without being forced to implement the other interface.
The dependency inversion principle states that a class should not depend on concrete classes, but rather on abstractions. In other words, we should not create dependencies on specific classes, but rather on interfaces or abstract classes.
For example, let's say we have a class that depends on a concrete database class. If we need to change the database, we'll also need to change the code of the class. This violates the dependency inversion principle.
A better way to design this would be to create a dependency on an abstract Database class. Then we can create a concrete MysqlDatabase class that extends Database. This way, we can change the database without having to change the code of the class.
In this article, we've looked at how the SOLID principles can be applied in Spring Boot development. These principles can help us write better code by making our code more maintainable and extensible.