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Q121. Is it a good design practice to have programming constructs like if and loops in constructor ?

Ans. I would avoid that. If we need to initialize member elements differently on the basis of some condition, I would prefer having overloaded constructors. I don't see a need to have a loop for initializing member elements unless the count of elements is huge and they all need to be initialized with common value.

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Q122. Is it a good Design practice to call methods from a constructor ?

Ans. Constructor's objective is to initialize member elements. If we don't deviate from that and don't have methods with logic in them, I don't see an issue with constructor's calling other methods assuming the methods are doing nothing but initialization. There are situations wherein we classify the member elements based on their type and hence having different initialization methods for different element types will give a better abstracted way to initialize them.

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Q123. Which is your favorite Design pattern, each in Creational , Structural and Behavioral and Why ?

Ans. [Open Ended Answer]

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Q124. Name few Behavioral Design Patterns ?

Ans. Interpreter,Chain of Responsibility,Command,Iterator,Observer,Mediator,Memento

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Q125. Name few structural Design Patterns ?

Ans. Adapter,Bridge,Composite,Decorator,Facade,Flyweight,Proxy

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Q126. Name few creational design patterns ?

Ans. Factory,Abstract Factory,Singleton,Prototype and Builder

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Q127. Design a Passport Office system

^{This question was recently asked at 'Netcracker Technology'.This question is still unanswered. Can you please provide an answer.}

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Q128. How would you do an object oriented design on animals in a zoo ?

^{This question was recently asked at 'Booking.com,InterContinental Hotels,Caissa,Workday'.This question is still unanswered. Can you please provide an answer.}

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Q129. Difference between Singleton and Factory Design Pattern ?

Ans. Both are creational design patterns but singleton facilitates in creation and reuse of single object whereas Factory deals with creation of multiple objects.

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Q130. Write a program to print two digit numbers that fulfil following criteria

Summing their digits and then multiplying with 3 should result in the number

For ex - 27 , (2+7) * 3 = 27

Ans. public class BuggyBread {
   public static void main(String args[]) {
      for(int x=10;x<100;x++){
         int tensDigit = x/10;
         int unitDigit = x%10;

         if((tensDigit+unitDigit)*3 == x){
            System.out.println(x);
         }
      }
   }
}

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Q131. What is a factory design pattern ?

Ans. Factory Design Patterns is the pattern that recommends creation of separate Factory Object for creation of other object.

So its like saying - If you want to create an object of ClassA, Talk to FactoryObject ( which is an object of FactoryClass ). FactoryObject in itself encapsulates the inputs and logic required to make the decision regarding the creation and construction of object.

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Q132. How to make sure that only one instance is created in Singleton Pattern ?

Ans. public class SingleTon {
private SingleTon() {
if (singleTon != null) {
throw new RuntimeException("cant not create the object");
}
}
public Object clone() throws CloneNotSupportedException {
throw new CloneNotSupportedException("can not be create");
}

static private volatile SingleTon singleTon;
public static SingleTon getInstance() {
SingleTon singleTon = this.sample;
if (singleTon == null) {
synchronized (this) {
singleTon = this.singleTon;
if (singleTon == null) {
singleTon = this.singleton = new SingleTon();
}
}
}
return singleTon;
}
}

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Q133. Design a Data Structure for a full text Search ?

^{This question was recently asked at 'Myntra'.This question is still unanswered. Can you please provide an answer.}

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Q134. Implement an LRU Cache ?

Ans. https://www.programcreek.com/2013/03/leetcode-lru-cache-java/

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Q135. Design an online shopping site system ?

Ans. AWS Services - CloudFront for distribution / caching, EC2 for computing, EBS for block storage , S3 for object storage , RDS for database , Kinesis for streaming , CloudWatch for monitoring.

Technologies - Java for back end with Spring Boot , Angular , RxJs for front end .

Architecture - Service Oriented. Multi layer.

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Very Frequently asked to Senior Software Engineers or Developers.

Q136. Describe some of the Design Patterns you have used ?

Ans. [Open Ended Answer]

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Q137. What is a responsive web design ?

Ans. Responsive web design is a approach to web design that allow desktop webpages to be viewed perfectly in different devices and sizes.

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Q138. Can you please provide an implementation of application level cache ?

Ans. We can use an expiration map whose entries gets expired after a certain interval and then we can put the logic to retrieve the entries if its expired in map. Alternatively we can create a separate class and make map its element. We can refresh the map in this class periodically by using a monitoring thread within static block.

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Q139. What is coupling and Cohesion ?

Ans. Coupling is the degree of interdependence between software modules, a measure of how closely connected two modules are or the strength of the relationships between modules.

Cohesion refers to the degree to which the elements of a module belong together. Cohesion measures the strength of relationship between pieces of functionality within a given module.

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Q140. Is it a Good practice to have application decision making in DAOs ?

Ans. No, DAO's should only have methods to perform CRUD operations. Application logic should reside in service methods.

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Q141. Have you ever felt the need of keeping the constructor private ?

Ans. Yes, When either we don't want an object to be created ( class having all static elements and hence not required ) or object to be created using a static method or static block. One such example could be a situation when we would like app to load objects at start up and we would like to restrict new object creation by any request.

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Q142. What are the advantages disadvantages of keeping config entries in database instead of property file and vice versa ?

Ans. Entries in DB will be retrieved at runtime unless a cache is maintained in application. Entries in File will be loaded to memory by default. Both can be implemented in 1 manner or other. By default property file will take space in memory, will be faster, and will require application restart on change. By Default DB config will be pulled at runtime, will be little slower, and doesn't require an application restart.

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Frequently asked Design Pattern interview question.

Q143. What is a prototype design pattern ?

Ans. The prototype pattern is a creational design pattern. It is used when the type of objects to create is determined by a prototypical instance, which is cloned to produce new objects. Prototype is used when we need duplicate copies of objects.

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Q144. Design a Library system ?

Ans. Following Tables can be created

ASSET - Entity Table With foreign key reference to Table AssetType

ASSET_TYPE - Entity Table specifying information related to Asset Type like Books, CDs etc.

MEMBER - Registration information for the member

MEMBERSHIP_TYPE - Membership Types provided by Library

MEMBERSHIP - Relation table with foreign key for MEMBER ,

MEMBERSHIP_TYPE

ASSET_ISSUE_LEDGER - Relationship between MEMBER and ASSET. This specify the issue of particular asset to a particular member.

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Q145. What are the advantages and disadvantages of Factory Design Pattern ?

Ans. Object Oriented Design Patterns is the science of identifying the pattern to make objects communicate in a way to effectively implement a Solution.

Factory Design Patterns is the pattern that recommends creation of separate Factory Object for creation of other object. So its like saying - If you want to create an object of ClassA, Talk to FactoryObject ( which is an object of FactoryClass ). FactoryObject in itself encapsulates the inputs and logic required to make the decision regarding the creation and construction of object.

Advantage of Factory Pattern - Loose Coupling and Segregation of Responsibilities. Now instead of hard binding the complete logic to decide the nature and shape of the object on the basis of some conditions, you are assigning the responsibility to some other object and hence making the relationship loosely coupled and hence main tenable.

Disadvantages - Before Understanding the Dis-advantages , we should understand that these patterns were chosen after a period of evolution and research and almost best fit for the required solution, otherwise these patterns would have easily been replaced by now.

Though the advantages of these pattern surpass the disadvantages keeping in mind the decreasing cost of resources and increasing scale of applications, but still loose coupling by means of additional objects results in decreased performance.

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Q146. Write a class explaining builder pattern ?

Ans.

public class BuggyBread { 



   private String element1; 



   private String element2; 



   private BuggyBread(String element1, String element2){ 

      this.element1 = element1; 

      this.element2 = element2; 

   } 



   public static class Builder { 

    

      private String element1; 



      private String element2; 



      Builder(BuggyBread buggybread){ 

         element1 = buggybread.element1; 

         element2 = buggybread.element2; 

      } 



      Builder withElement1(String element1){ 

         this.element1 = element1; 

         return this; 

      } 



      Builder withElement2(String element2){ 

         this.element2 = element2; 

         return this; 

      } 



      BuggyBread build(){ 

         BuggyBread buggybread = new BuggyBread(element1,element2); 

         return buggybread; 

      } 

   } 

}

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Q147. Can Enum be a replacement for a constant file in majority of the situation ?

Ans. Yes , it can be but it may not be an optimal alternative if we need to change the values frequently. As Enum is compiled like any Java File , any change requires the application to be rebuild , deployed and restart.

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Q148. Does it make sense to clone an object which is supposed to be immutable ?

Ans. It make sense only if we intend to modify either of the object and would like to preserve original state in other. Otherwise we can reuse the original object by making it singleton.

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Q149. What are design situations to use Singleton and Prototype Design Pattern ?

Ans. Both are creational design patterns.

Singleton is used when we would like to reuse an object if object is not supposed to hold request or thread specific information. Inversely Prototype is used in situations where we would like to reuse the object information but the request / thread may require it own data to be persisted.

In short, Singleton is used in situations where we can live with single object being shared across multiple requests or threads whereas Prototype is used when we need duplicate copies of objects.

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Frequently asked for Lead and Architect positions. Recently asked in many US companies.

Q150. What are Anti Patterns ?

Ans. Anti-pattern is simply the creation of a pattern in your coding that negatively affects your code i.e the Negatives surpasses the positives.

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