Common design patterns Ask in Software Engineer interview

 Common design patterns Ask in Software Engineer interview

The two most commonly asked design patterns in Software Engineering interviews are.

👉01. Singleton Design Pattern

👉02. Factory Design pattern 

Both the design pattern are creational design patterns it means It gives the way to create objects while hiding creation logic.

👉01. Factory Design Pattern

In the Factory design pattern, we create objects without exposing the creation logic to the client and refer to newly created objects using a common interface.

Steps in creating Factory design Pattern

Step 1: Create an interface

Shape.java

public interface Shape{

      void draw();

}

Step 2: Create a concrete class using the same interface.

Rectangle.java

public class Rectangle implements shape{

    @override

    public void draw(){

   sop("rectyange");  

   }

}

Square.java

public class Square implements shape{

    @override

    public void draw(){

   sop("Square");  

   }

}

Step 3: Create a factory to generate object

ShapeFactory.java

public class ShapeFactory{

public shape getShape(String shape){

       if(shape == null) return null;

       if(shape.equals("Square") ) return new Square();

       if(shape.equals("Rectangle")) return new Rectangle();

}

return null;

}

👉02. Singleton Design Pattern

Used to create singleton class and singleton class is a class that can have only one object at a time.

Steps to create Singleton design pattern

👉01. Mark the constructor private.

👉02. Create a private static class variable.

👉03. Create a public method to create an object after checking if the object is not already created.

Example:

class Singleton{

private static Singleton obj = null;

private Singleton(){}

public static singleton getInstance(){

     if(obj == null) obj = new Singleton();

return obj;

}

}

📓 We can make Singleton class thread-safe in the following ways:

👉 mark the method to get instance synchronized (WORST)

👉 mark the code block of creating an object as synchronized (BETTER)

👉 Create an instance using enum INSTANCE; (BEST)