Java Design Pattern Interview Questions [ MOST ASKED DESIGN PATTERN INTERVIEW QUESTIONS ]

Design Pattern Java Interview Questions and Answers for Experienced with examples.
Content covered -

Java Design Pattern Interview Questions part 2
https://youtu.be/QfnZGam76kE

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In Video of java interview questions and answers we have covered live real time coded example and flow charts to illustrate this and for better visual understanding. Content here is servers just theoretical purpose. Practical Real time examples with flow charts will be covered in video itself.
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This content covers step by step approach for beginners to experienced.

Q) What do we need Design pattern-
A) As Design Patterns are well documented and understood by software architects, designers and developers, then their application within a specific solution will likewise be well understood.

Patterns give a software developer an array of tried and tested solutions to common problems, thus reducing the technical risk to the project by not having to employ a new and untested design, thus saving time and effort during the implementation stage of the software development lifecycle

Q) What are the Creational Patterns?
Creational design patterns are related to the way of creating objects.
This pattern is used to define and describe how objects are created at class instantiation time

Q) What Is Factory Pattern?
In the Factory pattern, we don't expose the creation logic to the client and refer the created object using a standard interface.
The Factory Pattern is also known as Virtual Constructor.

Steps:
1) create main class which call factory class.
2) Factory class returns required class instance

Q) What Is Abstract Factory Pattern?
This factory is also called as factory of factories.
Abstract Factory lets a class returns a factory of classes.
So, this is the reason that Abstract Factory Pattern is one level higher than the Factory Pattern.

An Abstract Factory Pattern is also known as Kit.

Steps:
1) create main class which call factory of factory class.
2) Factory of factory / factory Producer creates instance of factory class.
3) Factory class returns required class instance

Q) What Is Singleton Design Pattern?
Singleton pattern is one of the simplest design patterns in Java.
This pattern involves a single class which is responsible to create an object while making sure that only single object gets created.
This class provides a way to access its only object which can be accessed directly without need to instantiate the object of the class.

Q) What Is Prototype Design Pattern?
Prototype pattern refers to creating duplicate object while keeping performance in mind.
It involves implementing a prototype interface which tells to create a clone of the current object.
This pattern is used when creation of object directly is costly. For example it requires data base calls or required too much of processing that will take a lot of memory.

What can be done ? : We can cache the object, returns its clone on next request

Steps:
1) create main class which call CacheImpl Class.
2) CacheImpl class has 2 methods : 1st to load the key value in map and create the cache. 2nd to return the required cloned object.
3) The main class , parent of all reuired concerete class contains cloning technique. Rest concrete class are normal POJOs, nothing special.
Q) What Is Builder Design Pattern?
Builder Pattern refers to approach that focuses on constructing a complex object from simple objects using step-by-step approach.

Major roles used in this design patterns are :
Complex Object / Final Product – e.g. house – complex object which we will generate with builder design pattern
Builder – abstract class / interface that defines all ways to create the product. It also has getFinalProduct method that will finally return complex object.
ConcreteBuilder – multiple Builder Impls that will give different final objects which are complex to design,
Director: Controls complex object creation. It has 2 main goals : 1st to call appropriate concrete builder class to create correct complex object. 2nd to return that complex object.

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