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Interview Questions and Answers - Order By Rating | ||||
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Ans. We can overload the main method by specifying different argument types. For example - 2 main methods with different arguments is perfectly legal public static void main(); public static void main(String[] args); The following are not legal as compiler will complain of duplicate methods public static void main(String[] args); public static void main(String[] args); Even The following are not legal as we cannot overload on return types public static String main(String[] args); public static void main(String[] args); | ||||
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Like Discuss Correct / Improve  main method Asked in 2 Companies | ||||
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Ans. Yes we can have a main method with string[] argument in every class of an application. When we execute an app we specify the starting point i.e the class that will get the control first and hence main method of that class gets executed. | ||||
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Like Discuss Correct / Improve  main method Asked in 3 Companies | ||||
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Ans. PATH, CLASSPATH and JAVA_HOME | ||||
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Like Discuss Correct / Improve  environment variables  path  classpath  java_home Asked in 3 Companies basic   frequent | ||||
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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. https://en.wikipedia.org/wiki/Database_normalization | ||||
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Like Discuss Correct / Improve  normalization  database Asked in 35 Companies intermediate   frequent | ||||
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Ans. PID - process identification number is an identification number that is automatically assigned to each process when it is created USER - User Name PR - PR is the process actual priority NI is the nice value, which is a user-space concept. VIRT -Virtual Image (kb). The total amount of virtual memory used by the task. RES - Resident size (kb). The non-swapped physical memory a task has used. SHR - Shared Mem size (kb). The amount of shared memory used by a task. S - Process Status. The status of the task which can be one of: D = uninterruptible sleep R = running S = sleeping T = traced or stopped Z = zombie %CPU - % CPU usage %MEM - % MEM Usage TIME - Total CPU time the task has used since it started. COMMAND - Command which was used to execute the process | ||||
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Like Discuss Correct / Improve  top command  unix command Asked in 1 Companies | ||||
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Ans. du -a /var | sort -n -r | head -n 10 | ||||
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Like Discuss Correct / Improve  unix command Asked in 1 Companies | ||||
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Ans. 59 23 28-31 * * [ "$(date +%d -d tomorrow)" = "01" ] && job_name | ||||
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Like Discuss Correct / Improve  unix  crontab Asked in 1 Companies | ||||
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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. 1. HashSet doesnt maintain its elements in any specific order and is all random whereas TreeSet maintains elements in natural order 9 order defined by the equals method of TreeSet element type ) 2. TreeSet doesnt allow null elements whereas HashMap does. 3. As TreeSet orders elements and is hence insertion is comparatively slower. 4. HashSet performs basic operations like add(), remove(), contains(), size() etc. in a constant size time. A TreeSet performs these operations at the order of log(n) time. 5. HashMap in Java internally backs a HashSet. A NavigableMap backs a TreeSet internally. | ||||
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Like Discuss Correct / Improve  collections  hashset  treeset  set   hashet vs treeset Asked in 4 Companies Basic   frequent | ||||
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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 | ||||
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. We can use external table feature of Oracle. | ||||
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Like Discuss Correct / Improve   Asked in 1 Companies Intermediate | ||||
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Ans. <a href="http://www.programcreek.com/2009/02/diagram-for-hierarchy-of-exception-classes/" rel="nofollow">http://www.programcreek.com/2009/02/diagram-for-hierarchy-of-exception-classes/</a> | ||||
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Like Discuss Correct / Improve  exception hierarchy   exceptions Asked in 3 Companies | ||||
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Ans. Enums in Java are used to declare predefined objects and then reuse them. they offer many benefits 1. Enum instance are type safe and thread safe. 2. Enum instances are singleton and hence reused. 3. If we use Enums with Switch , It makes sure that the passed argument is either of its instance and hence provides a safeguard. 4. If we use Enum with Sorted Collections we can sort the elements with a predefined priorities ( as per constant declaration in enum ) 5. We can use Enum as a Factory by defining its constructor. 6. We can store related constant data within enum. For example - If we know the values for the map upfront, we can alternatively use an enum. | ||||
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Like Discuss Correct / Improve   Asked in 6 Companies | ||||
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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 | ||||
Frequently asked question in companies using Rest Web services. | ||||
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Ans. PUT requests are only meant to place the object as it is on server. For example - You want a file to be uploaded and then placed in a particular folder or you want an Employee object to be persisted in the table. POST requests are also meant to transfer information from client to server but that information once received at the server is evaluated , modified or refactored before persisting. | ||||
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Like Discuss Correct / Improve  Put vs Post   Rest Asked in 5 Companies   frequent | ||||
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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 | ||||
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 across all type of companies and across all levels. | ||||
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Ans. Private - Not accessible outside object scope. Public - Accessible from anywhere. Default - Accessible from anywhere within same package. Protected - Accessible from object and the sub class objects. | ||||
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Like Discuss Correct / Improve  java   oop   access specifier   public   private   default   protected   public vs private vs default vs protected Asked in 12 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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