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

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

Q1. Design pattern used in 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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Q2. 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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Q3. When singleton can break and how to resolve it

Design

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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Q4. 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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Q5. Draw uml for singleton pattern.

Design

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

Design

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Q8. What is the difference between subject and observable ?

RxJava

Ans. Subject has state, it keeps a list of observers. On the other hand, an Observable is really just a function that sets up observation. While Subjects are Observables, Subjects also implement an Observer interface.

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Q9. What is the difference between Observer and Subscriber ?

Design

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Q10. Explain Facade design pattern

Design

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

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Q11. How one dao Implementation object (singleton) can handle multiple requests?

Design Pattern

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Q12. What are different types of dependency injections ?

Design

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

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Q13. 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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Q14. What could be the real world example of Adapter Design Pattern ?

Design

Ans. Voltage converters / Power Adapters

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Q15. 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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Q16. What are some uses of interceptors ?

Java EE

Ans. Authentication / Authorization
URL forwarding
Auditing / Logging
Localization

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Q17. 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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Q18. 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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Q19. Which is your favorite Design pattern, each in Creational , Structural and Behavioral and Why ?

Design

Ans. [Open Ended Answer]

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Q20. Name few Behavioral Design Patterns ?

Design

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

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Q21. Name few structural Design Patterns ?

Design

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

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Q22. Name few creational design patterns ?

Design

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

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Q23. 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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Q24. 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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Q25. 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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Very Frequently asked to Senior Software Engineers or Developers.

Q26. Describe some of the Design Patterns you have used ?

Design

Ans. [Open Ended Answer]

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Frequently asked Design Pattern interview question.

Q27. 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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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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Q29. 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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Q30. 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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