Design - Interview Questions and Answers for 'Pattern' | Search Java Interview Question

Design - Interview Questions and Answers for 'Pattern' - 57 question(s) found - Order By Newest

Almost sure to be asked in every company using any Dependency Injection framework ( Spring, Guice etc )

Q1. What is Dependency Injection or IOC ( Inversion of Control ) ?

Design

Ans. It is a Design Pattern that facilitates loose coupling by sending the dependency information ( object references of dependent object ) while building the state of the object. Objects are designed in a manner where they receive instances of the objects from other pieces of code, instead of constructing them internally and hence provide better flexibility.

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Q2. What are the Wrapper classes available for primitive types ?

Core Java

^Anonymous

Ans. boolean - java.lang.Boolean
byte - java.lang.Byte
char - java.lang.Character
double - java.lang.Double
float - java.lang.Float
int - java.lang.Integer
long - java.lang.Long
short - java.lang.Short
void - java.lang.Void

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Q3. Difference between Factory and Abstract Factory Design Pattern ?

Design

^Anonymous

Ans. Factory Pattern deals with creation of objects delegated to a separate factory class whereas Abstract Factory patterns works around a super-factory which creates other factories.

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Very frequently asked.Usually among first few questions.

Q4. What is MVC ?

Design

^Anonymous

Ans. MVC is a Design Pattern that facilititates loose coupling by segregating responsibilities in a Web application

1. Controller receives the requests and handles overall control of the request
2. Model holds majority of the Business logic, and
3. View comprise of the view objects and GUI component

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Q5. What Design pattern Wrapper Classes implement ?

Design

^Anonymous

Ans. Adapter.

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Q6. What are the disadvantages of Design Patterns ?

Design Pattern

^{2018-06-20 12:20:03}

Ans. 1. Design patterns are abstraction heavy and hence sometimes creates memory and performance overheads.

2. Sometimes they create unnecessary complexity without much added advantage.

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Q7. Difference between Factory and Builder Design Pattern ?

Design

^Anonymous

Ans. Builder pattern is the extension of Factory pattern wherein the Builder class builds a complex object in multiple steps.

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Q8. Difference between Proxy and Adapter ?

Design

^Anonymous

Ans. Adapter object has a different input than the real subject whereas Proxy object has the same input as the real subject. Proxy object is such that it should be placed as it is in place of the real subject.

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Q9. Difference between Adapter and Facade ?

Design

^Anonymous

Ans. The Difference between these patterns in only the intent. Adapter is used because the objects in current form cannot communicate where as in Facade , though the objects can communicate , A Facade object is placed between the client and subject to simplify the interface.

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Q10. Difference between Builder and Composite ?

^Anonymous

Ans. Builder is a creational Design Pattern whereas Composite is a structural design pattern. Composite creates Parent - Child relations between your objects while Builder is used to create group of objects of predefined types.

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Q11. Example of Chain of Responsibility Design Pattern ?

^Anonymous

Ans. Exception Handling Throw mechanism.

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Q12. Example of Observer Design Pattern ?

^Anonymous

Ans. Listeners.

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Q13. Difference between Factory and Strategy Design Pattern ?

Design

^Anonymous

Ans. Factory is a creational design pattern whereas Strategy is behavioral design pattern. Factory revolves around the creation of object at runtime whereas Strategy or Policy revolves around the decision at runtime.

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Q14. Shall we use abstract classes or Interfaces in Policy / Strategy Design Pattern ?

^Anonymous

Ans. Strategy deals only with decision making at runtime so Interfaces should be used.

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Q15. What are different types of dependency injections ?

Design

^{2017-11-07 09:37:47}

Ans. Setter injection
Constructor injection
Interface injection
Look-up method/method injection

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Q16. What's wrong with this code ?

public static void main(String[] args) {
String regex = "(\\w+)*";
String s = "Java is a programming language.";

Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(s);
while (matcher.next()) {
System.out.println("The e-mail id is: " + matcher.group());
}
}

Core Java

^{Admin
info@buggybread.com}

Ans. matcher.find() should have been used instead of matcher.next() within while.

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Q17. Which methods of the Pattern class have equivalent methods in the String class?

Core Java

^{Admin
info@buggybread.com}

Ans. split() and macthes()

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Very frequently asked. Usually followed by questions related to private constructor and synchronized access. Frequently asked in JPMorgan and TCS (Based on 2 feedback)

Q18. Explain Singleton Design Pattern ?

Design

^{Admin
info@buggybread.com}

Ans. http://www.buggybread.com/2014/03/java-design-pattern-singleton-interview.html

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Q19. Give an Example for Builder Pattern ?

Core Java

^{Admin
info@buggybread.com}

Ans. String str = new StringBuilder().append("Buggy").append("Bread").toString();

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Q20. Which of the following is not the difference between Singleton and Static class ( Class with static members only ) ?

a. Only one object can be created for Singleton class whereas No objects are created for static class.
b. Singleton class instance is initiated using new keyword whereas static class instance is created using static method.
c. Singleton class can be serialized whereas Static class cannot be.
d. Singleton Class can participate in runtime Polymorphism whereas Static class cannot.

^Anonymous

Ans. Singleton class instance is initiated using new keyword whereas static class instance is created using static method.

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Q21. Write code for singleton class

Design

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?keyword=singleton+class&category=code

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Q22. Write code for the usage of Builder Design Pattern

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?&category=code&searchOption&keyword=964

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

Q23. What are Anti Patterns ?

Design

^{2016-07-14 14:21:11}

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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Q24. What are design situations to use Singleton and Prototype Design Pattern ?

Design

^{2016-07-28 20:28:43}

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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Q25. Does it make sense to clone an object which is supposed to be immutable ?

Design

^{2016-07-28 20:54:59}

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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Q26. Write a class explaining builder pattern ?

Design

^{2016-08-17 10:32:03}

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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Q27. What are the advantages and disadvantages of Factory Design Pattern ?

Design

^{2016-09-07 09:19:26}

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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Frequently asked Design Pattern interview question.

Q28. What is a prototype design pattern ?

Design

^{2016-11-04 08:06:01}

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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Very Frequently asked to Senior Software Engineers or Developers.

Q29. Describe some of the Design Patterns you have used ?

Design

^{2016-12-01 16:31:17}

Ans. [Open Ended Answer]

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Q30. How to make sure that only one instance is created in Singleton Pattern ?

Core Java

^{2016-12-21 10:00:04}

Ans. By Using Double Checked Locking code

//Double Checked Locking Code
public static Singleton createInstance() {
if(singleton == null){
synchronized(Singleton.class) {
if(singleton == null) {
singleton = new Singleton();
}
}
}
return singleton;
}

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Q31. What is a factory design pattern ?

Design

^{2017-01-09 13:21:43}

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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Q32. Difference between Singleton and Factory Design Pattern ?

Design

^{2017-02-02 11:24:01}

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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Q33. Name few creational design patterns ?

Design

^{2017-02-12 16:06:15}

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

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Q34. Name few structural Design Patterns ?

Design

^{2017-02-12 16:07:00}

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

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Q35. Name few Behavioral Design Patterns ?

Design

^{2017-02-12 16:07:59}

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

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Q36. Which is your favorite Design pattern, each in Creational , Structural and Behavioral and Why ?

Design

^{2017-02-12 16:08:45}

Ans. [Open Ended Answer]

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Q37. Which are the most commonly used Design Patterns ?

Design

^{2017-03-10 10:42:50}

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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Q38. Explain Interceptor Design Pattern ?

Design

^{2017-05-06 19:23:08}

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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Q39. What are some uses of interceptors ?

Java EE

^{2017-05-06 19:26:02}

Ans. Authentication / Authorization
URL forwarding
Auditing / Logging
Localization

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Q40. What are the disadvantages of Adapter Design Pattern ?

Design

^{2017-05-07 08:43:19}

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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