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Design - Interview Questions and Answers for 'Design pattern' - 49 question(s) found - Order By Newest

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Very frequently asked.Usually among first few questions.
  Q1. What is MVC ? Design
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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Almost sure to be asked in every company using any Dependency Injection framework ( Spring, Guice etc )
  Q2. 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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   Like         Discuss         Correct / Improve     design patterns   ioc ( Inversion of Control )  dependency injection     Asked in 83 Companies      intermediate        frequent


 Q3. What are the Wrapper classes available for primitive types ?Core Java
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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   Like         Discuss         Correct / Improve     java   java5   data types   wrapper classes   adapter design pattern        rare


 Q4. Difference between Factory and Abstract Factory Design Pattern ?Design
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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 Q5. Difference between Factory and Builder Design Pattern ?Design
Ans. Builder pattern is the extension of Factory pattern wherein the Builder class builds a complex object in multiple steps.

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 Q6. What are the disadvantages of Design Patterns ?Design Pattern
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. What Design pattern Wrapper Classes implement ?Design
Ans. Adapter.

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 Q8. Difference between Proxy and Adapter ?Design
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
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 ?
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 ?
Ans. Exception Handling Throw mechanism.

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 Q12. Example of Observer Design Pattern ?
Ans. Listeners.

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 Q13. Difference between Factory and Strategy Design Pattern ?Design
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. What are different types of dependency injections ?Design
Ans. Setter injection
Constructor injection
Interface injection
Look-up method/method injection

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Very Frequently asked to Senior Software Engineers or Developers.
  Q15. Describe some of the Design Patterns you have used ?Design
Ans. [Open Ended Answer]

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   Like         Discuss         Correct / Improve     design patterns     Asked in 17 Companies      intermediate        frequent


 Q16. What are some uses of interceptors ?Java EE
Ans. Authentication / Authorization
URL forwarding
Auditing / Logging
Localization

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 Q17. When singleton can break and how to resolve itDesign
Ans. Deserialization. In serialization, we can save the object of a byte stream into a file or send over a network. Suppose if you serialize the Singleton class, and then again de-serialize that object, it will create a new instance, hence deserialization will break the Singleton pattern.

To overcome this issue, we need to override readResolve() method in the Singleton class and return the same Singleton instance.

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 Q18. If you are given choice to either load object eagerly or lazily , which one would you use in case of singleton pattern ?Design
Ans. I would choose Eager as the cost for 1 additional object is too minute for any such consideration.

Eager Loading results in Faster access ( Object available at load time) at the cost of additional space.

Lazy loading results in space saving ( Object available at first use ) at the cost of access speed.

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 Q19. Shall we use abstract classes or Interfaces in Policy / Strategy Design Pattern ?
Ans. Strategy deals only with decision making at runtime so Interfaces should be used.

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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)
  Q20. Explain Singleton Design Pattern ?Design
Ans. http://www.buggybread.com/2014/03/java-design-pattern-singleton-interview.html

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 Q21. Give an Example for Builder Pattern ?Core Java
Ans. String str = new StringBuilder().append("Buggy").append("Bread").toString();

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 Q22. 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.
Ans. Singleton class instance is initiated using new keyword whereas static class instance is created using static method.

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 Q23. Write code for singleton classDesign
Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?keyword=singleton+class&category=code

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 Q24. 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.
  Q25. What are Anti Patterns ?Design
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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 Q26. What are design situations to use Singleton and Prototype Design Pattern ?Design
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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 Q27. Does it make sense to clone an object which is supposed to be immutable ?Design
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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 Q28. What are the advantages and disadvantages of Factory Design Pattern ?Design
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.
 Q29. What is a prototype design pattern ?Design
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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 Q30. 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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