Design Principles
When designing object-oriented systems, it is important to follow certain principles to ensure that the code is well-structured, maintainable, and scalable. Two commonly used design principles are SOLID and DRY.
SOLID
SOLID is an acronym for five design principles: Single Responsibility, Open-Closed, Liskov Substitution, Interface Segregation, and Dependency Inversion.
Single Responsibility Principle (SRP) states that a class should have only one reason to change. It means that a class should have only one responsibility or job. This principle helps in making the code easier to understand, test, and maintain.
Open-Closed Principle (OCP) states that software entities (classes, modules, functions, etc.) should be open for extension but closed for modification. It means that the behavior of a module or class should be able to be changed without modifying its source code.
Liskov Substitution Principle (LSP) states that objects of a superclass should be able to be replaced with objects of its subclasses without affecting the correctness of the program. In other words, the subclasses should be substitutable for their base classes.
Interface Segregation Principle (ISP) states that clients should not be forced to depend on interfaces they do not use. It means that an interface should have only those methods that are relevant to the implementing classes. This principle helps in keeping the code modular and avoiding unnecessary dependencies.
Dependency Inversion Principle (DIP) states that high-level modules should not depend on low-level modules. Instead, both should depend on abstractions. It means that the code should depend on abstractions (interfaces or abstract classes) rather than concrete implementations. This principle helps in achieving loose coupling and making the code more flexible and maintainable.
DRY
DRY stands for Don't Repeat Yourself. It is a principle of software development that promotes the elimination of duplicated code. Repeated code increases the chances of introducing bugs and makes the code harder to maintain and understand. By following the DRY principle, developers can reduce redundancy by creating reusable and modular code.
By applying these design principles, you can create code that is modular, flexible, and easier to understand and maintain. Let's take a look at an example of applying the SOLID principles:
1// Example of applying SOLID design principles
2
3class Shape {
4 // ...properties and methods...
5}
6class Circle extends Shape {
7 // ...properties and methods specific to Circle...
8}
9class Rectangle extends Shape {
10 // ...properties and methods specific to Rectangle...
11}
12
13interface Drawable {
14 void draw();
15}
16
17class CircleDrawer implements Drawable {
18 private Circle circle;
19
20 public CircleDrawer(Circle circle) {
21 this.circle = circle;
22 }
23
24 public void draw() {
25 // Draw the circle
26 }
27}
28
29class RectangleDrawer implements Drawable {
30 private Rectangle rectangle;
31
32 public RectangleDrawer(Rectangle rectangle) {
33 this.rectangle = rectangle;
34 }
35
36 public void draw() {
37 // Draw the rectangle
38 }
39}
40
41public class Main {
42 public static void main(String[] args) {
43 Circle circle = new Circle();
44 Rectangle rectangle = new Rectangle();
45
46 List<Drawable> shapes = new ArrayList<>();
47 shapes.add(new CircleDrawer(circle));
48 shapes.add(new RectangleDrawer(rectangle));
49
50 for (Drawable shape : shapes) {
51 shape.draw();
52 }
53 }
54}xxxxxxxxxx}// Example of applying SOLID design principlesclass Shape { // ...properties and methods...}class Circle extends Shape { // ...properties and methods specific to Circle...}class Rectangle extends Shape { // ...properties and methods specific to Rectangle...}interface Drawable { void draw();}class CircleDrawer implements Drawable { private Circle circle; public CircleDrawer(Circle circle) { this.circle = circle; } public void draw() { // Draw the circle }}class RectangleDrawer implements Drawable {