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Interview Questions and Answers for 'Design' - 178 question(s) found - Order By Newest

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Very frequently asked. Among first few questions in almost all interviews. Among Top 5 frequently asked questions. Frequently asked in Indian service companies (HCL,TCS,Infosys,Capgemini etc based on multiple feedback )
  Q1. Difference between == and .equals() ?Core Java
Anonymous
Ans. "equals" is the method of object class which is supposed to be overridden to check object equality, whereas "==" operator evaluate to see if the object handlers on the left and right are pointing to the same object in memory.

x.equals(y) means the references x and y are holding objects that are equal. x==y means that the references x and y have same object.

Sample code:

String x = new String("str");
String y = new String("str");

System.out.println(x == y); // prints false
System.out.println(x.equals(y)); // prints true

  Sample Code for equals

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   Like         Discuss         Correct / Improve     java   string comparison   string   object class   ==    equals   object equality  operator     Asked in 289 Companies      basic        frequent

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Very Frequently asked. Have been asked in HCL Technologies very frequently ( based on 3 feedback ). Among first few questions in many interviews.
  Q2. Differences between abstract class and interface ?Core Java
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Ans. Abstract classes can have both abstract methods ( method declarations ) as well as concrete methods ( inherited to the derived classes ) whereas Interfaces can only have abstract methods ( method declarations ).

A class can extend single abstract class whereas it can implement multiple interfaces.

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   Like         Discuss         Correct / Improve     java   classes   abstract class   interfaces     Asked in 65 Companies      basic        frequent


 Q3. Let's suppose we have an to destroy objects, Design a program to implement garbage collection ?Design2017-08-04 14:08:01

Ans. Step 1 - We can create a Registry Class having Map of all created objects as key and References list as value.

Step 2 - Whenever we create an object , we should update the Registry in the constructor to add the new object.

Step 3 - Whenever we assign a new reference to the object , we need to update the entry in Map. Similarly if the reference get's removed ( end of scope etc ), we need to remove the entry of reference from the list.

Step 4 - We can have threaded code to monitor the Map to see if any object looses all it's references and should call the method to destroy object and clean the memory.

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   Like         Discuss         Correct / Improve     garbage collection


Almost sure to be asked in every company using any Dependency Injection framework ( Spring, Guice etc )
  Q4. 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 80 Companies      intermediate        frequent


 Q5. 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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   Like         Discuss         Correct / Improve     java   java5   data types   wrapper classes   adapter design pattern        rare


 Q6. 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.
  Q7. 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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 Q8. If you are given a choice to implement the code to either Insert a Record or Update if already exist, Which approach will you follow ?

1. Insert into the DB Table. If exception occurs, update the existing record.
2. Check if the record exists and update it if it exists, If not insert a new record.
Solution
admin
info@buggybread.com
Ans. In first case, there would be 2 DB calls in worst case and 1 in best case. In 2nd approach there will be always 2 DB calls.

Decision on the approach should depend on the following considerations -

1. How costly is the call to DB ? Are we using indices , hibernate etc

If calls to DB are costly , 1st approach should be the choice.

2. Exception Book keeping load upon exception.

The benefit of saving 1st call in approach 1 should be bigger than the Book keeping for the exception.

3. Probability of the exception in first apparoach.

If the DB Table is almost empty, it makes sense to follow Approach 1 as majority of the 1st calls will pass through without exception.

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   Like         Discuss         Correct / Improve     database   insert-update   db exceution plan   db strategy   design   architecture   technical lead


 Q9. In which cases , moving methods to utility class could be useful ?Core Java

Ans. It could be worthy to move a method to util class if the method needs to be shared, doesn't require polymorphic behavior and need not be overridden in special cases.

Don't belong to one group through is-a relationship ( You can share through parent class method )

Don't implement a specific interface ( java 8 default methods )

Doesn't involve complex computing as you will be loosing the benefit of object state with just static method.

Doesn't require polymorphic behavior as static methods don't participate in runtime polymorphism.

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   Like         Discuss         Correct / Improve     utility classes   util classes   static methods   application design        rare


 Q10. If you need to consume messages from the queue faster, which approach will you recommend - batching or concurrency ?Design2017-07-24 13:34:47

Ans. Each has it's own advantages

Batching requires less resources but may result in loosing whole batch in case of failure whereas concurrency even though is little more expensive in terms of resources but would result in minimal loss in case of failure.

In case messages are to be consumed in a particular order, batching them in that order and then consuming them makes better sense.

if incoming messages are not continuous , it makes more sense to do concurrency as we need not wait for all messages to form a batch and flush. Though time sensitivity can be added but that would add unnecessary complexity.

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   Like         Discuss         Correct / Improve     concurrency vs batching   concurrency  multithreading  batch


  Q11. What is the use of Transient Keyword ?Core Java
Anonymous
Ans. It in Java is used to indicate that a field should not be serialized.

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   Like         Discuss         Correct / Improve     java   oops   serialization   transient   java keywords     Asked in 38 Companies      intermediate        frequent

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 Q12. What Design pattern Wrapper Classes implement ?Design
Anonymous
Ans. Adapter.

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 Q13. What is the difference between these two approaches of creating singleton Class ?

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

//Single checked locking code
public static Singleton createInstance() {
   synchronized(Singleton.class) {
      if(singleton == null) {
         singleton = new Singleton();
      }
   }
   return singleton;
}
Design
Admin
info@buggybread.com
Ans. In First Case , Lock for the synchronized block will be received only if singleton == null whereas in second case every thread will acquire the lock before executing the code.
The problem of synchronization with singleton will only happen when the object has not be instantiated. Once instantiated , the check singleton == null will always generate true and the same object will be returned and hence no problem. First condition will make sure that synchronized access ( acquiring locks ) will only take place if the object has not been created so far.

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  Q14. What is coupling and Cohesion ?Design2016-11-15 16:16:10

Ans. Coupling is the degree of interdependence between software modules, a measure of how closely connected two modules are or the strength of the relationships between modules.

Cohesion refers to the degree to which the elements of a module belong together. Cohesion measures the strength of relationship between pieces of functionality within a given module.

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   Like         Discuss         Correct / Improve     coupling  cohesion     Asked in 10 Companies        frequent


 Q15. What are the benefits of Dependency Injection or IOC ?Design2017-06-23 11:51:20

Ans. Central place for configuring dependencies.

No need to create object, container manage all this By using Run time polymorphism and association.

Facilities development of framework / libraries by injecting implementation classes in the implementation code.

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   Like         Discuss         Correct / Improve     dependency injection  IOC  inversion of control


 Q16. What are the disadvantages of Design Patterns ?Design Pattern2018-06-20 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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 Q17. 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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 Q18. 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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 Q19. 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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 Q20. 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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 Q21. Example of Chain of Responsibility Design Pattern ?
Anonymous
Ans. Exception Handling Throw mechanism.

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 Q22. Example of Observer Design Pattern ?
Anonymous
Ans. Listeners.

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 Q23. 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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 Q24. 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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 Q25. What is a Listener ?Design
Anonymous
Ans. In GUI programming, an object that can be registered to be notified when events of some given type occur. The object is said to listener? for the events.

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 Q26. What are use cases?Process
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Ans. It is part of the analysis of a program and describes a situation that a program might encounter and what behavior the program should exhibit in that circumstance.

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 Q27. What is a Cursor ?Database
Admin
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Ans. It's a facility that allows traversal over the records pulled from a table or combination of tables. Its like iterator in Java.

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 Q28. 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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Very frequently asked. Usually followed by questions related to private constructor and synchronized access. Frequently asked in JPMorgan and TCS (Based on 2 feedback)
  Q29. Explain Singleton Design Pattern ?Design
Admin
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Ans. http://www.buggybread.com/2014/03/java-design-pattern-singleton-interview.html

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 Q30. Shouldn't we make a class with all static members is its just expected to be executed as a standalone program with just one thread. Moreover Lets assume that there is no runtime Polymorphism required and there is no need for serialization ?Design
Admin
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Ans. Still No in case we are making use of inheritance. we may have problem wherein we have program flow moving across common inherited method and specific methods of the derived class. call made to another static method in the parent class will only access the static class of the Parent class irrespective of the call from any of the derived class.

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   Like         Discuss         Correct / Improve     static class   static vs singleton   inheritance


 Q31. Give an Example for Builder Pattern ?Core Java
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Ans. String str = new StringBuilder().append("Buggy").append("Bread").toString();

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 Q32. Which UML diagrams you usually use for design ?Design
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Ans. Use Case Diagram, Component Diagram for High level Design and Class Diagram , Sequence Diagram for low level design.

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 Q33. What kind of software architecture your organization follow ?Design
Admin
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Ans. We have multi tier architecture with multiple layers , We have series of web servers and applications in application tier, infrastructure libraries at middle tier and Database servers at the lower tier. We are using Oracle as Database, ESB ( Enterprise service Bus ) for asynchronous communication and Rest Web Services.

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 Q34. 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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 Q35. What are the fail safe systems ?Operating System2016-06-09 09:29:43

Ans. Fail Safe systems are tolerant systems that continue processing even if they sense any problem. the objective here is to continue with the processing even if there are some problems instead of completely shutting it down. Example could be to catch an exception and still letting it complete with partial results.

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   Like         Discuss         Correct / Improve     fail safe systems   system design   exception handling     Asked in 3 Companies


 Q36. Explain TDD or Test Driven Design ?Design

Ans. TDD is a development process that involves short iterations: first an automated test case is written. Then, the code is written to pass that test, and finally one refactors the new code to acceptable standards.

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Frequently asked in face to face interviews.
  Q37. Write a program to print fibonacci series.Core Java

Ans. int count = 15;
int[] fibonacci = new int[count];
fibonacci[0] = 0;
fibonacci[1] = 1;
for(int x=2; x < count; x++){
fibonacci[x] = fibonacci[x-1] + fibonacci[x-2];
}

for(int x=0; x< count; x++){
System.out.print(fibonacci[x] + " ");
}

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   Like         Discuss         Correct / Improve     ebay   fibonacci series     Asked in 66 Companies      basic        frequent


 Q38. Write code for singleton classDesign

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

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   Like         Discuss         Correct / Improve     singleton  code  coding  design pattern     Asked in 1 Companies      Intermediate        frequent


 Q39. 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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   Like         Discuss         Correct / Improve     builder design pattern  builder pattern  code  coding      intermediate


 Q40. What are the fail fast systems ?2016-06-09 09:31:27

Ans. Fail fast systems are intolerant systems that fails at the first instance of smelling any problem. The objective here is to break the system instead of continuing with the possibly flawed processing. Example could be breaking the processing upon an exception.

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   Like         Discuss         Correct / Improve     fail fast systems   system design     Asked in 1 Companies


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