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Design - Interview Questions and Answers for 'At' - 120 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 in HCL Tech ( Based of 4 inputs )
  Q2. Write a Program to reverse a string iteratively and recursivelyCore Java

Ans. Using String method -

new StringBuffer(str).reverse().toString();

Iterative -

Strategy - Loop through each character of a String from last to first and append the character to StringBuilder / StringBuffer

public static String getReverseString(String str){
StringBuffer strBuffer = new StringBuffer(str.length);
for(int counter=str.length -1 ; counter>=0;counter--){
strBuffer.append(str.charAt(counter));
}
return strBuffer;
}

Recursive -

Strategy - Call the method with substring starting from 2nd character recursively till we have just 1 character.

public static String getReverseString(String str){
if(str.length <= 1){
return str;
}
return (getReverseString(str.subString(1)) + str.charAt(0);
}

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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.
  Q3. Differences between abstract class and interface ?Core Java
Admin
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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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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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 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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 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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  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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 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 disadvantages of Design Patterns ?Design Pattern2018-06-20 12:20:03

 This question was recently asked at 'Bloomberg'.This question is still unanswered. Can you please provide an answer.


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 Q16. 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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 Q17. 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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 Q18. 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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 Q19. 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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 Q20. Example of Chain of Responsibility Design Pattern ?
Anonymous
Ans. Exception Handling Throw mechanism.

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 Q21. Example of Observer Design Pattern ?
Anonymous
Ans. Listeners.

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 Q22. 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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 Q23. 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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 Q24. 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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 Q25. 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)
  Q26. 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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 Q27. 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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 Q28. 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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 Q29. 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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 Q30. 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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Frequently asked in face to face interviews.
  Q31. 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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 Q32. Write code for singleton classDesign

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

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 Q33. 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


Frequently asked for Lead and Architect positions. Recently asked in many US companies.
  Q34. What are Anti Patterns ?Design2016-07-14 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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 Q35. What are design situations to use Singleton and Prototype Design Pattern ?Design2016-07-28 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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 Q36. Does it make sense to clone an object which is supposed to be immutable ?Design2016-07-28 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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   Like         Discuss         Correct / Improve     clone  clone objects  prototype design pattern   immutable  immutability  immutability  cloning


 Q37. Write a class explaining builder pattern ?Design2016-08-17 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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 Q38. What are the advantages and disadvantages of Factory Design Pattern ?Design2016-09-07 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.
 Q39. What is a prototype design pattern ?Design2016-11-04 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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   Like         Discuss         Correct / Improve     design pattern  prototype design pattern  cloning     Asked in 11 Companies      intermediate


 Q40. Have you ever felt the need of keeping the constructor private ?Design2016-11-15 09:40:58

Ans. Yes, When either we don't want an object to be created ( class having all static elements and hence not required ) or object to be created using a static method or static block. One such example could be a situation when we would like app to load objects at start up and we would like to restrict new object creation by any request.

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