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Interview Questions and Answers - Order By Rating | ||||
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Ans. [Open Ended Answer] The objective of the question is to check how efficient one is in the language so that appropriate level questions are asked. Don't tell too high number if you are being interviewed for a junior or mid level position as the interviewer may throw advance level questions. | ||||
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Like Discuss Correct / Improve   Asked in 17 Companies | ||||
Frequently asked in Cognizant ( Based on 2 feedback ) | ||||
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Ans. Inner join is the intersection of two tables on the condition defined by the where clause i.e will get records from both tables matched by a column. Outer join is the union of two tables i.e will get all records from both tables and will put null in the columns where related records are not present. Left Outer join is the left union of two tables i.e all records from the table on the left and values from the right table for related records else null for the columns from right table. Right Outer join is the right union of two tables i.e all records from the table on the right and values from the left table for related records else null for the columns from left table. | ||||
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Like Discuss Correct / Improve  sql  inner join  outer join  right join  left join Asked in 24 Companies basic   frequent | ||||
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Ans. An Exception in java is the occurrence during computation that is anomalous and is not expected. Exception handling is the mechanism which is used to handle such situations. | ||||
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Like Discuss Correct / Improve  exception handling Asked in 18 Companies basic   frequent | ||||
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Ans. Ant is procedural, we need to provide information about what to do and when to do through code. Maven is declarative, everything is defined in the pom file. | ||||
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Like Discuss Correct / Improve  maven  maven vs ant Asked in 1 Companies | ||||
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Ans. Maven is a build automation tool used primarily for Java projects. | ||||
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Like Discuss Correct / Improve  maven  build Asked in 6 Companies basic   frequent | ||||
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Ans. <a href="http://javahungry.blogspot.com/2015/03/difference-between-array-and-arraylist-in-java-example.html" rel="nofollow">http://javahungry.blogspot.com/2015/03/difference-between-array-and-arraylist-in-java-example.html</a> | ||||
Sample Code for ArrayList | ||||
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Like Discuss Correct / Improve  array  arraylist Asked in 11 Companies basic   frequent | ||||
Very Frequently asked to Senior Software Engineers or Developers. | ||||
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Ans. [Open Ended Answer] | ||||
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Like Discuss Correct / Improve  design patterns Asked in 17 Companies intermediate   frequent | ||||
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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 | ||||
Basic and Very Frequently asked. | ||||
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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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Frequently asked Design Pattern interview question. | ||||
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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 | ||||
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Ans. The external tables feature is a complement to existing SQL Loader functionality. It enables to access data in external sources as if it were in a table in the database. We have used it few times for replicating tables across different database systems. | ||||
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Like Discuss Correct / Improve  external table oracle Asked in 1 Companies   rare | ||||
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Ans. GET is supposed to get information from the server. Client sends the minimal information so that Server can respond with the response body on basis of request. For example - You want to get complete employment record for employee id 123 POST is supposed to send the information for submission. Payload or a Body is usually sent so that it can be persisted on the server. For example - Sending the complete information of an employee ( id, name , dept etc ) to the server for persisting it. | ||||
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Like Discuss Correct / Improve  get vs post   web service   rest Asked in 11 Companies basic   frequent | ||||
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Ans. Earlier any class implementing an interface was supposed to implement all methods declared in an interface. There was no place for optionally implementing all or subset of methods.Though we have abstract classes wherein we could have provided such a mechanism by declaring some methods as abstract while providing definition for some. But as Abstract classes have a body and are comparatively heavier than interfaces and interfaces associate closely to the concept of providing interfacing than abstract classes, Java might have though of providing optional implementation for default methods. This way same interface can be reused in variety of ways rather than making copies of an interface to suit different needs. | ||||
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Like Discuss Correct / Improve  java 8   java8  interface default methods  default methods Asked in 6 Companies | ||||
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Ans. Fail-fast iterators detect illegal concurrent modification during iteration and fail quickly and cleanly rather than risking arbitrary, non deterministic behavior at an undetermined time in future. Example could be of an Iterator failing if it smells ConcurrentModificationException. | ||||
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Like Discuss Correct / Improve  fail-fast Iterators  Iterators Asked in 5 Companies intermediate | ||||
Frequently asked. Among first few questions in the J2EE segment of interview. | ||||
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Ans. Deployment Descriptor which is usually web.xml is used to specify the classes, resources and configuration of the application and how the web server uses them to serve web requests.This file is usually added to WEB-INF folder and contains following * Servlet entries and url mapping * Plugins * Some info regarding authentication / filters * Landing Page * Event Handlers | ||||
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Like Discuss Correct / Improve  web.xml   servlets  deployment descriptor Asked in 15 Companies basic   frequent | ||||
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Ans. A cookie is a small piece of text stored on a user's computer by the browser for a specific domain. Commonly used for authentication, storing site preferences, and server session identification. | ||||
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Like Discuss Correct / Improve  cookie   javascript   web application   session management   browser   j2ee Asked in 16 Companies basic   frequent | ||||
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Ans. Simple Inner Class, Local Inner Class, Anonymous Inner Class, Static Nested Inner Class. | ||||
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Like Discuss Correct / Improve  java   inner classes   classes Asked in 6 Companies basic   frequent | ||||
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Very frequently asked. Favorite question in Walk in Drive of many Indian service companies. | ||||
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Ans. They are different the way their elements are stored in memory. TreeMap stores the Keys in order whereas HashMap stores the key value pairs randomly. | ||||
Sample Code for treemap Sample Code for hashmap | ||||
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Like Discuss Correct / Improve  java   collections   map   treemap   hashmap   treemap vs hashmap Asked in 31 Companies basic   frequent | ||||
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Frequently asked in Indian Service Companies. Tech Mahindra ( Based on 3 inputs ) and Infosys ( 3 inputs ) | ||||
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Ans. List - Members are stored in sequence in memory and can be accessed through index. Set - There is no relevance of sequence and index. Sets doesn't contain duplicates whereas multiset can have duplicates. Map - Contains Key , Value pairs. | ||||
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Like Discuss Correct / Improve  java   collections   list   set   map   list vs set vs map Asked in 8 Companies basic   frequent | ||||
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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 ) and Epam Systems | ||||
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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 294 Companies basic   frequent | ||||
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Frequently asked at HCL Technologies ( Based on 3 feedback ) | ||||
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Ans. Checked exceptions are the exceptions for which compiler throws an errors if they are not checked whereas unchecked exceptions are caught during run time only and hence can't be checked. | ||||
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Like Discuss Correct / Improve  java   exceptions   checked exceptions   unchecked exceptions   exception handling   checked vs unchecked exceptions Asked in 39 Companies basic   frequent | ||||
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Very frequently asked. Favorite question in Walk in Drive of many Indian service companies. | ||||
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Ans. Its a method which cannot be overridden. Compiler throws an error if we try to override a method which has been declared final in the parent class. | ||||
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Like Discuss Correct / Improve  java   oops   final   final method Asked in 30 Companies basic   frequent | ||||
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Very frequently asked across all types of companies. | ||||
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Ans. Hashtable is synchronized whereas HashMap is not.HashMap allows null values whereas Hashtable doesnt allow null values. | ||||
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Like Discuss Correct / Improve  java   collections   hashmap   map   hashtable   hashmap vs hashtable Asked in 14 Companies basic   frequent | ||||
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Frequently asked in Infosys India | ||||
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Ans. String pool (String intern pool) is a special storage area in Java heap. When a string is created and if the string already exists in the pool, the reference of the existing string will be returned, instead of creating a new object and returning its reference. | ||||
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Like Discuss Correct / Improve  java   oops   string   string class   string pool   heap memory Asked in 31 Companies intermediate   frequent | ||||
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Ans. There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference | ||||
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Like Discuss Correct / Improve  java   data types   casting  type casting   basic interview question Asked in 8 Companies basic   frequent | ||||
Very frequently asked. Usually asked in different variants like Diff between StringBuffer , String Builder ; Difference between StringBuilder and String class; Choice between these classes etc. | ||||
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Ans. A string buffer implements a mutable sequence of characters. A string buffer is like a String, but can be modified. At any point in time it contains some particular sequence of characters, but the length and content of the sequence can be changed through certain method calls. The String class represents character strings. All string literals in Java programs, such as "abc" are constant and implemented as instances of this class; their values cannot be changed after they are created. | ||||
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Like Discuss Correct / Improve  java   string   stringbuffer   frequently asked Asked in 18 Companies basic   frequent | ||||
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Advanced level question usually asked in High end product companies. Have been asked in Google and Amazon (Based on 1 Feedback) | ||||
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Ans. The Java runtime environment deletes objects when it determines that they are no longer being used. This process is known as garbage collection. The Java runtime environment supports a garbage collector that periodically frees the memory used by objects that are no longer needed. The Java garbage collector is a mark-sweep garbage collector that scans Java dynamic memory areas for objects, marking those that are referenced. After all possible paths to objects are investigated, those objects that are not marked (i.e. are not referenced) are known to be garbage and are collected. | ||||
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Like Discuss Correct / Improve  java   garbage collection   java memory management   advanced Asked in 21 Companies intermediate   frequent | ||||
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Very frequently asked to Fresh graduates. | ||||
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Ans. 1.Abstraction solves the problem at design level while encapsulation solves the problem at implementation level 2.Abstraction is used for hiding the unwanted data and giving relevant data. while Encapsulation means hiding the code and data into a single unit to protect the data from outside world. 3. Abstraction lets you focus on what the object does instead of how it does it while Encapsulation means hiding the internal details or mechanics of how an object does something. 4.For example: Outer Look of a Television, like it has a display screen and channel buttons to change channel it explains Abstraction but Inner Implementation detail of a Television how CRT and Display Screen are connect with each other using different circuits , it explains Encapsulation. | ||||
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Like Discuss Correct / Improve  java   oops   oops concepts   encapsulation  object oriented programming (oops)  oops concepts   abstraction   basic interview question   encapsulation vs abstraction Asked in 10 Companies basic   frequent | ||||
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Very Frequently asked to fresh graduates and less experienced. Favorite question in Walk in drives. Frequently asked in Indian Services companies. | ||||
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Ans. Overloading - Similar Signature but different definition , like function overloading. Overriding - Overriding the Definition of base class in the derived class. | ||||
Sample Code for overloading Sample Code for overriding | ||||
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Like Discuss Correct / Improve  java   oops   overloading   overriding   oops concepts   basic interview question   overloading vs overriding Asked in 86 Companies basic   frequent | ||||
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Ans. Vectors are synchronized whereas Array lists are not. | ||||
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Like Discuss Correct / Improve  java   basic interview question   vector   arraylist   collections   synchronization   vector vs arraylist Asked in 35 Companies basic   frequent | ||||