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Ans. Component methods called by the container to notify the component of the events

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Q2163. What is the difference between authentication and authorization ?

Authentication

Ans. Authentication is the process of verifying the identity and credentials of the user to authenticate him into the system.

whereas

Authorization is the process by which access to a segment , method or resource is determined.

Authorization is usually a step next to authentication.

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Q2164. What is archiving ?

Process

Ans. It's the process of preserving the state of an object and then restoring it.

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Q2165. What is an applet ?

Ans. Applet is a J2EE component or a tiny application that gets executed in a widget engine ( like browser )

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Q2166. What does the Web module contains ?

Ans. JSP files, media files and deployment descriptor ( web.xml )

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Q2167. What are the different J2EE modules ?

Ans. 1. Application Client Module
2. Web Module
3. EJB
4. Resource Adapter

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Q2168. What is the difference between

File f = new File("homexyz.txt");

and

File f = File.createTempFile("xyz",".txt","home"); ?

Ans. First will not create physical file in storage whereas the second will.

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Q2169. Can you name some of the Java frameworks in different domains ?

Frameworks

Ans. Web Framework - Spring , Struts, Play
Dependency Injection frameworks - Google Guice , PicoContainer and Dagger
ORM Framework - Hibernate
Big Data / ETL Frameworks - Apche Hadoop , Apache Crunch, Apache Spark.
View Frameworks - JSF , Apache Wicket,jtwig.
Java Gui Frameworks - SWT , AWT, JavaFX
Testing - Junit, Mockito, PowerMock, EasyMock, JMock, JMockit
Rest Web services - Jersey , Restlet , RestX, RestEasy ,Restfulie

Here is the big list for reference - http://javasearch.buggybread.com/home2.php?keyword=

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Q2170. What are the benefits of creating immutable objects ?

Ans. 1. Security and Safety - They can be shared across multiple threads as they are thread safe. Moreover, it protects then from bad state due to interception by the other code segment. One such problem due to mutability and access by alternate code segment could be the change of hash code and then the impact on its search with hash collections.

2. Reuse - In some cases they can be reused as only one copy would exist and hence it can be relied upon. For example - String Pool

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Q2171. How does Lazy Initialization helps improving performance of an application ?

Hibernate

Ans. Lazy Initialization means , Load Dependencies when required. Which means less load on application resources as only required data is loaded upfront. It's not only good for better performance but for better resource utilization too.

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Q2172. What are the points to be considered if we move from Eager initialization to Lazy Initialization in Hibernate ?

Hibernate

Ans. Make sure that the properties of dependent Hibernate entities are not accessed and if yes, better wrap the whole code within single transaction.

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Q2173. What are some advantages of Scala ?

Ans. Scala code is more concise and hence easy to read and maintain. It supports all features of functional programming and provide a pure object oriented way of application creation. It is ideal for creating all scales of applications. It is inter operable with Java code and hence can import / use Java libraries and frameworks.

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Q2174. Does Scala code compile to be Java Byte Code ?

Ans. Yes, that's the reason Scala code is inter operable with Java and they run smoothly with each other in JVM.

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Q2175. What is Scala ?

Ans. Scala is a general purpose programming language that runs on JVM. Its completely inter operable with Java, purely object oriented and has full support for functional programming and a strong static type system.

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Q2176. What are the similarities and differences between Scala and Java ?

Ans. Similarities - Both and Object Oriented and Statically typed languages that runs on JVM.

Difference - Unlike Java, Scala is a Pure Object Oriented language as it doesn't use primitives and static variables.Unlike Java 8 which supports some functional programming concepts, Scala provides support for all functional programming concepts. Java 8 does not support Pattern Matching, Function Currying etc

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Usually asked to entry level software developers.

Q2177. Write a program to swap two variables without using third

Ans. public static void main(String[] args) {
   int num1 = 1;
   int num2 = 2;
   num1 = num1^num2;
   num2 = num1^num2;
   num1 = num1^num2;
   System.out.print("num1 = " + num1 +", num2 = "+num2);
}

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Q2178. What is a binary tree ?

Algorithm

Ans. Binary tree is a tree in which each node has up to two children.Tree is a data structure composed of nodes.Each tree has a root node(not necessary in graph theory). The root node has zero or more child nodes.Each child node has zero or more child nodes, and so on.The tree cannot contain cycles.

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Q2179. Write an algorithm / Java Program to show duplicates in an array of n elements?

Algorithm

Ans. int duplicateArray[] = { 1, 2, 2, 3, 4, 5, 6, 8, 9}
Set unique = new HashSet();
for (int i = 0; i < duplicateArray.length; i) {
if (unique.contains(duplicateArray[i])) {
System.out.println(duplicateArray[i]);
} else {
unique.add(duplicateArray[i]);
}
}

Complexity O(n) = nHashSet contains and add has O(n) = 1

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Q2180. Write an algorithm / java program for Heap Sort ?

Algorithm

Ans. https://www.geeksforgeeks.org/heap-sort/

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Q2181. What is memory leak ? How Java helps countering memory leaks compared to C++ ?

Ans. Memory Leak is a situation wherein we have a reserved memory location but the program has lost its reference and hence has no way to access it.

Java doesn't have concept of Pointers, Moreover Java has concept of Garbage collection that frees up space in heap that has lost its references.

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Q2182. Can we override wait() or notify() methods?

Ans. wait and notify are declared final in object class and hence cannot be overridden.

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Q2183. Can we have only try block in java ?

Ans. No, It should be followed by either catch or finally.

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Q2184. Does Java supports Default arguments ?

Ans. No

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Q2185. How should we handle errors while writing or accessing Stored Procedures?

Database

Ans. Store Procedure returns the error code. Moreover we can put the call withing try block and catch SQL Exception.

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Q2186. Explain dot(.) operator ?

Ans. Its used to access the object properties using the object reference or class properties using the Class Name. Moreover its used to access the classes and Interfaces of a package.

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Q2187. What is a class and object ?

or

How would you explain a fresher the concept of class and object in simple terms ?

Ans. Class is a template using which objects are created in memory. It's kind of a mold using which objects with body / state are made.

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Q2188. Have you heard of SiteMesh ?

Ans. Sitemesh is a web page layout and decoration framework by OpenSymphony. SiteMeshFilter can intercept the requests and then build UI components (based on configuration) then renders the final page.

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Q2189. What is the difference between filter and filter-mappings xml tag within deployment descriptor ?

Ans. filter tag speficies the filter name and respective class for handling filter action whereas filter mapping maps the filter to the url patterns ( specifying the url that needs to be intercepted )

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Q2190. What is a Servlet Filter ?