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

Interview Questions and Answers - Order By Newest

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

Q31. 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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Q32. 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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Q33. Write a class explaining builder pattern ?

Design

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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Frequently asked Design Pattern interview question.

Q34. 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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Q35. 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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Q36. 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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Q37. 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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Q38. Name few creational design patterns ?

Design

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

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Q39. Name few structural Design Patterns ?

Design

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

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Q40. Name few Behavioral Design Patterns ?

Design

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

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Q41. Which is your favorite Design pattern, each in Creational , Structural and Behavioral and Why ?

Design

Ans. [Open Ended Answer]

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Q42. 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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Q43. 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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Q44. 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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Q45. What could be the real world example of Adapter Design Pattern ?

Design

Ans. Voltage converters / Power Adapters

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Q46. What are the trade offs between public constructor and static final method ?

Core Java

Ans. Public constructor is simple and easy as it's the default way of object creation. So there are no additional coding overheads as compiler provides the default constructor if none is provided by coder.

With static final methods, it facilitates loose coupling by segregating the responsibility of object creation to a separate method. Validation can be done on the constructor arguments before calling it. Moreover if any adaption on the arguments is required that can achieved easily with factory method.On the flip side, there is coding overhead and additional method call.

Sample Code for constructor

Sample Code for factory

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Q47. What are the worst anti patterns in Java ?

Design

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

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Q48. How one dao Implementation object (singleton) can handle multiple requests?

Design Pattern

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Q49. Explain Facade design pattern

Design

Ans. Single gateway of the entire application is called Facade Design Pattern.

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Q50. What is the difference between Observer and Subscriber ?

Design

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

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Q51. Design a Program to clone an object and all it's children.

Design

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Q52. Draw uml for singleton pattern.

Design

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

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Q53. What is MVC in GUI components ?

Design

Ans. The Model/View/Controller pattern, a strategy for dividing responsibility in a GUI component.

The model is the data for the component.

The view is the visual presentation of the component on the screen.

The controller is responsible for reacting to events by changing the model.

According to the MVC pattern, these responsibilities should be handled by different objects.

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Q54. If you have to pull a sub string out of a string, which method would you use - using String methods or Pattern / Matcher ?

Design

Ans. It depends on how complex it is and if in future it would need any sort opf debugging. It's not easy to debug code if it's making heavy use of shortcuts like Lambda , Patterns etc.

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Q55. Design pattern used in struts.

Struts

Ans. Struts controller uses the Command design pattern and the action classes use the Adapter design pattern. The process() method of the RequestProcessor uses the Template method design pattern.

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Q56. With the following code, Which is a valid way to initialize ?
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;
      }
   }
}