SOLID in Software Development - 4

Interface Segregation Principle (ISP)

The Interface Segregation Principle (ISP) is one of the five SOLID principles of object-oriented programming (OOP). It states that "Many client-specific interfaces are better than one general-purpose interface." In other words, we should avoid creating large, monolithic interfaces that expose a lot of functionality that not all clients need. Instead, we should create smaller, more specific interfaces that only expose the functionality that a particular client needs.

here is an example of how the Interface Segregation Principle (ISP) can be violated:

public interface Shape {
    void draw();
    void resize();
    void rotate();
    void translate();
}

public

class

Circle

implements

Shape

{
    private

double radius;

    public

Circle(double radius)

{
        this.radius = radius;
    }

    @Override


public

void draw() {
        // Draw a circle
    }

    @Override
    public void resize() {
        // Resize the circle
    }

    @Override
    public void rotate() {
        // Rotate the circle
    }

    @Override
    public void translate() {
        // Translate the circle
    }
}

public

class

Triangle

implements

Shape

{
    private

double sideA;
    private

double sideB;
    private

double sideC;

    public

Triangle(double sideA, double sideB, double sideC)

{
        this.sideA = sideA;
        this.sideB = sideB;
        this.sideC = sideC;
    }

    @Override


public

void draw() {
        // Draw a triangle
    }

    @Override
    public void resize() {
        // Resize the triangle
    }

    @Override
    public void rotate() {
        // Rotate the triangle
    }

    @Override
    public void translate() {
        // Translate the triangle
    }
}

The Shape interface defines five methods: draw, resize, rotate, translate, and getArea. However, not all shapes support all of these methods. For example, a circle does not support the getArea method, and a triangle does not support the rotate method. This violates the ISP because it forces all shapes to implement methods that they do not support.

A better way to design this code would be to create separate interfaces for each type of shape:

public interface Drawable {
    void draw();
}

public interface Resizable {
    void resize();
}

public interface Rotatable {
    void rotate();
}

public interface Translatable {
    void translate();
}

public interface Shape extends Drawable, Resizable, Translatable {
    double

getArea();
}

public

class

Circle

implements

Shape

{
    private

double radius;

    public

Circle(double radius)

{
        this.radius = radius;
    }

    @Override
    public void draw() {
        // Draw a circle
    }

    @Override
    public void resize() {
        // Resize the circle
    }

    @Override
    public void translate() {
        // Translate the circle
    }

    @Override
    public double getArea() {
        return Math.PI * radius * radius;
    }
}

public

class

Triangle

implements

Shape

{
    private

double sideA;
    private

double sideB;
    private

double sideC;

    public

Triangle(double sideA, double sideB, double sideC)

{
        this.sideA = sideA;
        this.sideB = sideB;
        this.sideC = sideC;
    }

    @Override


public

void draw() {
        // Draw a triangle
    }

    @Override
    public void resize() {
        // Resize the triangle
    }

    @Override
    public void translate() {
        // Translate the triangle
    }

    @Override
    public double getArea() {
        // Calculate the area of the triangle
    }
}

This code follows the ISP because the Shape interface only defines methods that are common to all shapes, and the Drawable, Resizable, Rotatable, and Translatable interfaces define methods that are specific to certain types of shapes. This allows us to only implement the methods that are relevant to a particular shape, and it makes our code more modular and easier to maintain.

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