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Q61. How is static and dynamic polymorphism achieved in Java ?

Ans. Static polymorphism is the polymorphic resolution identified at compile time and is achieved through function overloading whereas dynamic polymorphism is the polymorphic resolution identified at runtime and is achieved through method overriding.

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Q62. What is a Destructor ? Do we have Destructors in Java ?

Ans. Destructor is used to de-allocate memory allocated by objects.

There are no destructors in Java. Alternatively, Java provides Automatic garbage collection i.e automatically releasing the un-referenced memory.

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Q63. Write a java program to implement Quick sort ?

Ans. http://www.programcreek.com/2012/11/quicksort-array-in-java/

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Frequently asked to Fresh graduates.

Q64. Write a program to implement Binary search ?

Ans. http://algs4.cs.princeton.edu/11model/BinarySearch.java.html

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Q65. Which data structure would you recommend for ordered and sorted data?

Ans. TreeSet and TreeMap are used for maintaining sorted elements.

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Q66. Explain Exception Hierarchy in Java SE ?

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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Q67. What is a Database Procedure ?

Ans. Stored procedures are a batch of SQL statements along with programming constructs ( if else, loops etc ) and stored as a single program that can be called by different clients and hence reused.

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Q68. What is a Database sequence ?

Ans. Its a feature wherein database creates unique values incremental values to be stored as primary key for the table.

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Q69. What do you know about JQuery ?

Ans. jQuery is a cross platform JavaScript library designed to simplify the client-side scripting of HTML. JQuery is the most popular JavaScript library.

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Q70. Can we have try statement without catch? If try statement contains return will the finally block be executed? What happens if there is an exception inside finally block?

Ans. Yes, with finally.

Yes, finally block will be executed even if there is no exception in try block.

If finally throws an exception, the exception gets thrown to the calling module.

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Very Frequently asked to fresh graduates and less experienced.

Q71. What are the principle concepts of Object Oriented Programming ?

Ans. Abstraction Polymorphism Inheritance Encapsulation

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All these acronyms JDK,JRE,JVM etc are very frequently asked.

Q72. Difference between JDK and JRE ?

Ans. JRE or Java Runtime Environment is the Java Virtual Machine on which class files are executed. It includes borwser plugins that facilitates execution of class files in browsers.

JDK or Java Development Kit includes JRE , compiler and development tools.

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Q73. What are the benefits of Enums ?

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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Q74. What are the disadvantages of multithreading ?

Ans. 1. Switching Overheads - Even though multi threading aims at improving performance by reducing the wait time and hence improving overall throughput, there is a cost of switching resources between threads and sometime this cost can surpass the benefits if there isnt much wait for IO or external communication.

2. Debugging is hard with multi threaded code.

3. Deadlock - Execution of multi threaded code many a times lead to deadlock due to shared resources.

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Q75. What is Spring Boot ?

Ans. Spring Boot is Springs convention-over-configuration solution for creating stand-alone, production-grade Spring-based Applications.

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Q76. What is an exception and exception handling in Java ?

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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Q77. Explain Generics in Java ?

Ans. Generics are a facility of generic programming that were added to the Java programming language in 2004 within J2SE5.0. They allow "a type or method to operate on objects of various types while providing compile-time type safety.

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Q78. Explain OOps concepts.

Ans. There are four main OOP concepts in Java. These are:

Abstraction. Abstraction means using simple things to represent complexity. We all know how to turn the TV on, but we don?t need to know how it works in order to enjoy it. In Java, abstraction means simple things like objects, classes, and variables represent more complex underlying code and data. This is important because it lets avoid repeating the same work multiple times.

Encapsulation. This is the practice of keeping fields within a class private, then providing access to them via public methods. It?s a protective barrier that keeps the data and code safe within the class itself. This way, we can re-use objects like code components or variables without allowing open access to the data system-wide.

Inheritance. This is a special feature of Object Oriented Programming in Java. It lets programmers create new classes that share some of the attributes of existing classes. This lets us build on previous work without reinventing the wheel.

Polymorphism. This Java OOP concept lets programmers use the same word to mean different things in different contexts. One form of polymorphism in Java is method overloading. That?s when different meanings are implied by the code itself. The other form is method overriding. That?s when the different meanings are implied by the values of the supplied variables. See more on this below.

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Q79. What is the use of second level cache in Hibernate ?

Ans. Second level cache is shared between sessions. Hibernate by default uses first level cache. Second level cache need to be configurd to use.
There are several second level cache e.g eh cache,jboss cache etc.

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Q80. When to use List, Set and Map in Java

Ans. I. If we want a Collection that does not store duplicate values, then we use a Set based collection.

II. If we want to frequently access elements operations based on an index value then we use a List based collection. E.g. ArrayList

III. If we want to maintain the insertion order of elements in a collection then we use a List based collection.

IV. For fast search operation based on a key, value pair, we use a HashMap based collection.

V. If we want to maintain the elements in a sorted order, then we use a TreeSet based collection.

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Q81. What does System.exit() do ?

Ans. Generally used to indicate termination

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Q82. What are the benefits of Junits ?

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Q83. How you can check Object is created or not in case of Singleton using Object class method ?

Ans. Reflections-- setAccesible--avoid using enumns

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Q84. Explain different inheritance mapping strategies with JPA / Hibernate.

Ans. table per hierarchy
table per concrete class
table per sub class

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Q85. How would you securely migrate a database to RDS?

Amazon Web Services (AWS)

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Q86. Describe AWS VPC and subnets.

Amazon Web Services (AWS)

Ans. VPC stands for Virtual Private Cloud. You can define a VPC and subnets for a region in AWS and that can be used to access shared resources on the cloud. For eg: API gateway to access any file on S3.

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Q87. What is your experience with AWS EMR ?

Amazon Web Services (AWS)

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Q88. How many objects are created when we define a bean with two different name in spring?

Ans. we wont create the objects because of each and every bean will be an object

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Q89. What are different types of Polymorphism in Java ?

Ans. run time polymorphism
compile time polymorphism

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Q90. Is String mutable or immutable in Java ?

Ans. String is Immutable because of String Constant Pool.

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