Interview Questions and Answers for 'Design' | Search Interview Question

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Frequently asked Design Pattern interview question.

Q61. 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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Q62. What are the advantages disadvantages of keeping config entries in database instead of property file and vice versa ?

Design

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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Q63. Have you ever felt the need of keeping the constructor private ?

Design

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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Q64. Is it a Good practice to have application decision making in DAOs ?

Design

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

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Q65. Can you please provide an implementation of application level cache ?

Design

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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Q66. What is a responsive web design ?

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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Q67. Design an online shopping site system ?

Design

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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Q68. Implement an LRU Cache ?

Design

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

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Q69. How to make sure that only one instance is created in Singleton Pattern ?

Core Java

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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Q70. What is a factory design pattern ?

Design

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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Q71. 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

Core Java

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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Q72. Difference between Singleton and Factory Design Pattern ?

Design

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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Q73. Design a Passport Office system

Design

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

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Q74. Name few creational design patterns ?

Design

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

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Q75. Name few structural Design Patterns ?

Design

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

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Q76. Name few Behavioral Design Patterns ?

Design

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

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Q77. Which is your favorite Design pattern, each in Creational , Structural and Behavioral and Why ?

Design

Ans. [Open Ended Answer]

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Q78. Is it a good Design practice to call methods from a constructor ?

Design

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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Q79. Is it a good design practice to have programming constructs like if and loops in constructor ?

Design

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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Q80. Which are the most commonly used Design Patterns ?

Design

Ans. Builder ( While Writing Unit Tests )
Prototype ( Cloning )
Adapter ( asList , toString )
Chain Of Responsibility ( Logging )
Singleton
Factory ( Action Mapping )
Proxy
Observer ( Event Listener )
MVC ( Web frameworks )
Filter ( Criteria )

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Try 1 Question(s) Test

Q81. What should be the intended sequence in which elements and methods should be declared in a class ?

Design

Ans. static final variables
public variables ( though it should be avoided )
private variables
constructor
public methods
private methods.

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Q82. Is it a good practice to override static methods ?

Design

Ans. Though it's useful but it's not as useful as overriding member or object methods. We cannot achieve polymorphic behavior with static methods by overriding their definition in derived class.

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Q83. How do you prefer to keep names for classes and interfaces ?

Design

Ans. I like to keep the names in Capital Camel case. Moreover I prefer to keep the names for classes, enums and interfaces such that they are easily distinguishable just by the pattern of their names.

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Q84. How can we prevent duplicate object creation in Java?

Design

^{This question is still unanswered. Can you please provide an answer.}

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Q85. Create an object oriented design using classes and interfaces to show relationship in a Sport tournament ?

Design

^{This question is still unanswered. Can you please provide an answer.}

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Q86. What is "convention over configuration" ? Which framework uses this design paradigm ?

Design

Ans. Convention over configuration is a way of software design used by frameworks that attempt to decrease the number of decisions that a developer is required to make without necessarily losing flexibility. The objective is to reduce the unnecessary configurations and follow conventions to accomplish that. For example - DB Entity and DB Table name conventionally should be same and hence shouldn't require configuring mapping between the two.

"Spring Boot" and "Ruby on Rails" have adopted this design principle.

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Q87. Are there any disadvantages of "Convention over configuration" Design paradigm ?

Design

Ans. Yes, It may result in some loss of flexibility as the application has to follow all conventions. Moreover it can contradict with other design paradigms or principles used in the application or framework.

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Q88. Can you give an example of "Convention over configuration" Design principle ?

Design

Ans. Hibernate mapping configurations are used for mapping hibernate entities and corresponding DB Tables. Conventionally Entities and Table can share the same name and hence framework can provide implicit mapping instead of explicit mapping through configurations. Though it may result in little loss of flexibility in extreme cases but will work with all applications following the convention.

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Q89. Explain Interceptor Design Pattern ?

Design

Ans. It is used for intercepting the request. It's primary use is to implement security policy. All or specific request types can be intercepted and hence forwarded to authentication / authorization module so as to facilitate authorized requests to application.

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Q90. What are the disadvantages of Adapter Design Pattern ?

Design

Ans. It introduces a layer of adaptations before it reaches the final and desired interface.

Moreover sometimes all requests are forwarded to adapter class. Some of such requests doesn't even require any sort of adaptions as they are qualified to call the final interface directly and introducing overheads.

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