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Interview Questions and Answers - Order By Rating

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 Q1801. Can you give a real world example of Encapsulation and Abstraction ?Core Java
Ans. Car Engine is an example of encapsulation and abstraction. You ignite the car using an interface called starter and least bothered about how the tire actually moves (This is abstraction). The engine encapsulates the complete process to itself only and doesn't allow you to start the other components like the radiator etc ( this is excapsulation )

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   Like         Discuss         Correct / Improve     encapsulation  object oriented programming (oops)  oops concepts  abstraction  oops  oops features  java features     Asked in 13 Companies

 Q1802. Does compiler treats it differently if we don't prefix this to the member element and its implicit as its the only variable available with that name ?
Ans. It makes no difference whether we add this to the variable or not. The only use of this is in the cases where there are multiple variables with the same name and we want to distinguish between the member variable and local variable. In case this is not added ,this is automatically added by the compiler in the byte code.

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   Like         Discuss         Correct / Improve     this keyword  member elements  member variables

This question can be asked in different variants like performace improvement of an application, improving performance for DB communication etc.
 Q1803. What are the ways in which execution time of the code can be improved ?Solution
Ans. This depends on entirely upon the code type. For example

1.If its just logic, we can try it to short circuit or put the if / switch case with maximum probability in the beginning.

2. Can use faster data structures, for eg - random retrieval instead of sequence / iterator

3. Working with primitive types or even bytes instead of Objects, even though it may result in marginal improvement.

4. If its service call, then service call with bulk load can help

5. If DB Operation, then with use of Indices , Views or using ORM , cache etc.


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   Like         Discuss         Correct / Improve     performance improvement  code optimization     Asked in 1 Companies

 Q1804. Which of the following Java features facilitates Dependency Injection - Inheritance or Composition ?
Ans. Composition for sure. Inheritance in case the reference of a parent class is used. If its interface, no Inheritance involved.

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   Like         Discuss         Correct / Improve     dependency injection  IOC

 Q1805. What is the difference between declaration, instantiation and initialization ?Core Java
Ans. Declaration is intimation to the compiler about the nature of Data a reference is going to hold.

For example - List myList;

Instantiation is reservation of memory.

For example

myList = new ArrayList();

Initialization or construction is setting the default values for member elements.

For example

myList = new ArrayList(mySet);

** Example 2nd is both for instantiation as well as initialization. The only difference is that 2nd will initialized the member elements to their default values whereas 3rd will initialized it with the elements from set.


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   Like         Discuss         Correct / Improve     declaration   instantiation   initialization   construction   declaration vs instantiation   instantiation vs initialization   declaration vs initialization     Asked in 1 Companies      basic        frequent

 Q1806. What are different types of variables in Java ?
Ans. 1. Function Local Variables
2. Instance Variables
3. Class variables or static variables

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   Like         Discuss         Correct / Improve     variables     Asked in 1 Companies      basic        frequent

  Q1807. What is a cookie ?Java EE
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

  Q1808. What are the different types of inner classes ?Core Java
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.
  Q1809. Difference between TreeMap and HashMap ?Core Java
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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Frequently asked in Indian Service Companies. Tech Mahindra ( Based on 3 inputs ) and Infosys ( 3 inputs )
  Q1810. What is the difference between List, Set and Map ?

or

What are the different Java Collections Interfaces ?		Core Java
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.
  Q1811. Difference between Public, Private, Default and Protected ?Core Java
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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 Q1812. What is servlet Chaining ?Java EE
Ans. Multiple servlets serving the request in chain.

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   Like         Discuss         Correct / Improve     java   web application   servlets     Asked in 1 Companies        rare

 Q1813. What are the Wrapper classes available for primitive types ?Core Java
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

 Q1814. What are concepts introduced with Java 5 ?Core Java
Ans. Generics , Enums , Autoboxing , Annotations and Static Import.

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 Q1815. Does Constructor creates the object ?Core Java
Ans. New operator in Java creates objects. Constructor is the later step in object creation. Constructor's job is to initialize the members after the object has reserved memory for itself.

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   Like         Discuss         Correct / Improve     java   constructor   object creation      intermediate        rare

 Q1816. Can static method access instance variables ?Core Java
Ans. Though Static methods cannot access the instance variables directly, They can access them using instance handler.

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   Like         Discuss         Correct / Improve     static   static method   java   oop   variables     Asked in 1 Companies      basic        frequent

  Q1817. 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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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
  Q1818. 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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Frequently asked at HCL Technologies ( Based on 3 feedback )
  Q1819. Difference between Checked and Unchecked exceptions ?Core Java
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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Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q1820. What is a Final Variable ?Core Java
Ans. Final variable is a variable constant that cannot be changed after initialization.

  Sample Code for final variable

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 Q1821. Which String class does not override the equals() and hashCode() methods, inheriting them directly from class Object?Core Java
Ans. java.lang.StringBuffer.

  Sample Code for StringBuffer

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Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q1822. What is a final method ?Core Java
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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 Q1823. Which interface does java.util.Hashtable implement?Core Java
Ans. Java.util.Map

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Frequently asked.
  Q1824. What is an Iterator?Core Java
Ans. Iterator is an interface that provides methods to iterate over any Collection.

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   Like         Discuss         Correct / Improve     java   collections   iterator     Asked in 11 Companies      basic        frequent

 Q1825. Which interface provides the capability to store objects using a key-value pair?Core Java
Ans. java.util.map

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Very frequently asked across all types of companies.
  Q1826. Difference between HashMap and Hashtable?Core Java
Ans. Hashtable is synchronized whereas HashMap is not.HashMap allows null values whereas Hashtable doesnt allow null values.

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 Q1827. Does java allow overriding static methods ?Core Java
Ans. No. Static methods belong to the class and not the objects. They belong to the class and hence doesn't fit properly for the polymorphic behavior.

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   Like         Discuss         Correct / Improve     java   oops   static   static method   overriding      intermediate
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 Q1828. When are static variables loaded in memory ?Core Java
Ans. They are loaded at runtime when the respective Class is loaded.

  Sample Code for static variable

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 Q1829. Can we serialize static variables ?Core Java
Ans. No. Only Object and its members are serialized. Static variables are shared variables and doesn't correspond to a specific object.

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 Q1830. What will this code print ?

String a = new String ("TEST");
String b = new String ("TEST");
if(a == b) {
System.out.println ("TRUE");
} else {
System.out.println ("FALSE");
}		Core Java
Ans. FALSE. == operator compares object references, a and b are references to two different objects, hence the FALSE. .equals method is used to compare string object content.

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   Like         Discuss         Correct / Improve     string   string class   java   ==   object references   coding     Asked in 2 Companies      basic        frequent
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