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Interview Questions and Answers for 'Redis' - 19 question(s) found - Order By Newest

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 ) and Epam Systems
  Q1. Difference between == and .equals() ?Core Java
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   == vs equals   equals vs ==     Asked in 293 Companies      basic        frequent

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Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q2. What is the difference between ArrayList and LinkedList ?Core Java
Ans. Underlying data structure for ArrayList is Array whereas LinkedList is the linked list and hence have following differences -

1. ArrayList needs continuous memory locations and hence need to be moved to a bigger space if new elements are to be added to a filled array which is not required for LinkedList.

2. Removal and Insertion at specific place in ArrayList requires moving all elements and hence leads to O(n) insertions and removal whereas its constant O(1) for LinkedList.

3. Random access using index in ArrayList is faster than LinkedList which requires traversing the complete list through references.

4. Though Linear Search takes Similar Time for both, Binary Search using LinkedList requires creating new Model called Binary Search Tree which is slower but offers constant time insertion and deletion.

5. For a set of integers you want to sort using quicksort, it's probably faster to use an array; for a set of large structures you want to sort using selection sort, a linked list will be faster.

  Sample Code for ArrayList

  Sample Code for LinkedList

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   Like         Discuss         Correct / Improve     collections   java   data structures   arraylist   linkedlist   arraylist vs linkedlist     Asked in 61 Companies      Basic        frequent

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Basic and Very Frequently asked.
  Q3. What is Polymorphism in Java ?Core Java
Ans. Polymorphism means the condition of occurring in several different forms.

Polymorphism in Java is achieved in two manners

1. Static polymorphism is the polymorphic resolution identified at compile time and is achieved through function overloading whereas

2. Dynamic polymorphism is the polymorphic resolution identified at runtime and is achieved through method overriding.

  Sample Code for overloading

  Sample Code for overriding

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   Like         Discuss         Correct / Improve     polymorphism  object oriented programming (oops)  oops concepts  oops concepts     Asked in 108 Companies      Basic        frequent

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 Q4. Difference between Predicate, Supplier and Consumer ? Core Java
Ans. Predicate represents an anonymous function that accepts one argument and produces a result.

Supplier represents an anonymous function that accepts no argument and produces a result.

Consumer represents an anonymous function that accepts an argument and produces no result.

  Sample Code for Predicate

  Sample Code for Supplier

  Sample Code for Consumer

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   Like         Discuss         Correct / Improve     java   java8   predicate   consumer   supplier   lambda expression   predicate vs consumer vs supplier      expert


  Q5. Does Java support Multiple Inheritance ?Core Java
Ans. Java doesn't support multiple inheritance. Interfaces does't facilitate inheritance and hence implementation of multiple interfaces doesn't make multiple inheritance.

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   Like         Discuss         Correct / Improve     java   oop   oop concepts   inheritence   multiple inheritence   basic interview question     Asked in 10 Companies      basic        frequent

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  Q6. Why java doesn't support multiple Inheritance ?

or

Explain Java Diamond Problem.
Core Java
Ans. class A {
void test() {
System.out.println("test() method");
}
}

class B {
void test() {
System.out.println("test() method");
}
}

Suppose if Java allows multiple inheritance like this,

class C extends A, B {
}

A and B test() methods are inheriting to C class.

So which test() method C class will take? As A & B class test() methods are different , So here we would Facing Ambiguity.

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   Like         Discuss         Correct / Improve     multiple inheritance  object oriented programming (oops)  oops concepts  diamond problem     Asked in 20 Companies      basic        frequent


 Q7. What is PermGen or Permanent Generation ?Core Java
Ans. The memory pool containing all the reflective data of the java virtual machine itself, such as class and method objects. With Java VMs that use class data sharing, this generation is divided into read-only and read-write areas. The Permanent generation contains metadata required by the JVM to describe the classes and methods used in the application. The permanent generation is populated by the JVM at runtime based on classes in use by the application. In addition, Java SE library classes and methods may be stored here.

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   Like         Discuss         Correct / Improve     java   jvm   memory management   permgen   permanent generation   advanced   architecture     Asked in 9 Companies      expert


 Q8. What are some different logging levels for log4j ?Log4j
Ans. DEBUG
ERROR
ALL
WARN
INFO
FATAL
OFF
TRACE
TRACE_INT
WARN

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   Like         Discuss         Correct / Improve     java   log4j   log4j level   logging   error logging     Asked in 10 Companies


 Q9. What is the difference between log4j and java logging api.Log4j
Ans. log4j is by apache while java logging api is given by sun. log4j is more powerful,extensible and simple to use than java logging api.

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   Like         Discuss         Correct / Improve          Asked in 1 Companies


 Q10. What are the advantages and disadvantages of CopyOnWriteArrayList ?Core Java
Ans. This collections class has been implemented in such a manner that it can never throw ConcurrentModificationException. As it performs update and write operations by creating a new copy of ArrayList, It's slower compared to ArrayList.

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   Like         Discuss         Correct / Improve     java   collections   list   arraylist   copyonwritearraylist   advantages-disadvantages   ConcurrentModificationException     Asked in 4 Companies      Expert


  Q11. How is multiple inheritance implemented in Java ?Core Java
Ans. There was no multiple inheritance in java before version 8 as implementing multiple interfaces cannot be termed as inheritance.

With Java 8 , came the concept of default methods wherein the class implementing the interface carries the default implementation from the interface and hence facilitating multiple inheritance.

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   Like         Discuss         Correct / Improve     multiple inheritance  object oriented programming (oops)  oops concepts   inheritance  object oriented programming (oops)  oops concepts   oops concept     Asked in 10 Companies        frequent


 Q12. What is Dirty read in Database Transactions ?Database
Ans. A dirty read occurs when a transaction is allowed to read data from a row that has been modified by another running transaction but not yet committed.

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   Like         Discuss         Correct / Improve     database transaction     Asked in 8 Companies


 Q13. What is Redis ?Redis
Ans. Redis is an in-memory data structure store, used as a database, cache and message broker.

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   Like         Discuss         Correct / Improve     redis


 Q14. What is replication in Redis ? why do we need it ?Redis
Ans. Asynchronous Replication of information from master to all slaves. Redis is an in memory storage and hence any crash may result in complete loss of information on a cluster.

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   Like         Discuss         Correct / Improve     Redis  replication in redis     Asked in 1 Companies


 Q15. What is the difference between Oracle , Cassandra and Redis ?Database
Ans. Oracle is a relational database. Cassandra is a noSQL Database whereas Redis is an inmemory cache.

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   Like         Discuss         Correct / Improve     oracle  casandra  redis


 Q16. How can we check all fields and values for a particular Redis key ? Redis
Ans. HGETALL <key>

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   Like         Discuss         Correct / Improve     Redis  check fields and value for a key


 Q17. How can we get count of all keys within Redis ?Redis
Ans. We can either do DBSIZE or KEYS *

Keys * will return the list of all keys too so DBSIZE is preferred if we just want the count.

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   Like         Discuss         Correct / Improve     Redis  Count All Keys  DBSIZE  Keys *


 Q18. How can we set a key within Redis ?Redis
Ans. SET <KEY_NAME> <VALUE>

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   Like         Discuss         Correct / Improve     redis  setting a key


 Q19. Do you know how can we export Redis data ?Redis
 This question is still unanswered. Can you please provide an answer.


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   Like         Discuss         Correct / Improve     Amazon Web Services (AWS)  Redis  Memcache



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