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Q1201. Write a class explaining builder pattern ?

Ans.

public class BuggyBread { 



   private String element1; 



   private String element2; 



   private BuggyBread(String element1, String element2){ 

      this.element1 = element1; 

      this.element2 = element2; 

   } 



   public static class Builder { 

    

      private String element1; 



      private String element2; 



      Builder(BuggyBread buggybread){ 

         element1 = buggybread.element1; 

         element2 = buggybread.element2; 

      } 



      Builder withElement1(String element1){ 

         this.element1 = element1; 

         return this; 

      } 



      Builder withElement2(String element2){ 

         this.element2 = element2; 

         return this; 

      } 



      BuggyBread build(){ 

         BuggyBread buggybread = new BuggyBread(element1,element2); 

         return buggybread; 

      } 

   } 

}

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Q1202. What is the difference between = and == in Java ?

Core Java

Ans. = is the assignment operator that assigns the result of the expression on the right to the variable on the left, whereas

== is the operator to check object equality to see if the reference on left and right are pointing to the same object. For primitive types, its used to check if both variables holds the same value.

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Q1203. How is == operator different for objects and primitive types ?

Core Java

Ans. For objects or references, == operator check if the reference on left and right points to the same object.

For primitive types or variables, == operator check if the variable on left and right holds the same value.

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Q1204. What are the benefits of Enums ?

Core Java

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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Q1205. Have you heard of Ban Duplicate Classes Maven enforcer plugin ? What is its use ?

Maven

Ans. Yes , we have been using this plugin with our projects and its purpose is to warn and stop the Build if there are duplicates of the same package and class are being carried either directly or through transitive dependencies. the duplicate could be coming through different types of dependencies or through different versions of the same dependency. Its purpose is to make sure that there is only one copy thats being used at compile time and runtime and hence shouldnt later result in runtime problems.

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Q1206. How to tackle duplicate classes in maven build ?

Maven

Ans. The simplest way is to ignore them if Maven enforcer plugin is complaining about it but it may lead to runtime problems later.

We can do the dependency:tree to see from where these duplicate ones are coming and hence can exclude the duplicate one.

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Q1207. What are different dependency scopes in Maven ?

Maven

Ans. Compile

This is the default scope. Compile dependencies are available in all classpaths of a project. Moreover, these dependencies are propagated to dependent projects.

Provided

This is much like compile, but indicates you expect the JDK or a container to provide the dependency at runtime.

Runtime

This scope indicates that the dependency is not required for compilation, but is for execution.

Test

This scope indicates that the dependency is is only available for the test compilation and execution phases. This scope is not transitive.

System

This scope is similar to provided except that you have to provide the JAR which contains it explicitly.

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Q1208. What are the build lifecycles of Maven ?

Maven

Ans. Default , Clean and Site.

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Q1209. Why Collection interface does not extend Cloneable interface ?

Core Java

Ans. Here is the list of classes that implements Collections Interface - http://www.buggybread.com/2015/02/java-collections-classes-that-implement.html

Having Collection interface to extend Cloneable interface would mean necessarily implement clone method by all implementing classes. As not all collection classes allow duplicate elements, it makes no sense to clone elements for them.

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Q1210. What happens to the Exception object after the exception handling is done ?

Core Java

Ans. As with all other objects its garbage collected after its usage unless its rethrown.

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Q1211. What are the disadvantages of multithreading ?

Core Java

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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Q1212. What is the difference between Controller and Task Command ?

IBM WCS

Ans. Controller Command is the command that gets called upon a request, just like We have actions in struts and controller in Spring. Task is a step in this bigger process. Task command are the commands that perform specific task for a controller command, like service classes in other frameworks. In order to complete the request, a controller command may invoke multiple task commands.

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Q1213. Which is the root interface of Collection classes in Java ?

Core Java

Ans. java.util.Collection

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Q1214. What is the difference between URI, URL and URN ?

Java EE

Ans. URI stands for Uniform Resource Indicator
URL stands for Uniform Resource Locator
URN stands for Uniform Resource Name

URI = URL + URN

For ex - http://javasearch.buggybread.com/InterviewQuestions/questionSearch.php?keyword=url

This is URI. The string from start till .php is URL whereas keyword=url is URN.

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Q1215. In this url

http://javasearch.buggybread.com/InterviewQuestions/questionSearch.php?searchOption=label&keyword=url

What is protocol , domain , path and query param ?

Java EE

Ans. the web URI starts with the protocol which is http in this case, javasearch.buggybread.com is the domain in this case which is a subdomain of buggybread.com, /InterviewQuestions is the path, questionSearch.php is the resource, searchOption and keyword are query params.

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Q1216. What is the character limit of url and doesn it apply to GET and POST Requests ?

Java EE

Ans. Its 2048 and Yes it applies to get request but not POST. As in Get Request , elements are passed as part of the url, this limit applies to Get requests.

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Q1217. Write code for Binary tree traversal ?

Core Java

Ans. http://javabeat.net/binary-search-tree-traversal-java/

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Q1218. Explain what happens when insertion is performed in case of ArrayList and LinkedList.

Data Structure

Ans. Array List works on Array and when we add an element in middle of the list, Array List need to update the index of all subsequent elements. I the capacity is full, it even may need to move the whole list to a new memory location . Linked List works on Double linked list algorithm and all it has to do is to adjust the address of the previous and next elements.

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Q1219. How to Bulk upload the data into Oracle database?

Database

Ans. We can use external table feature of Oracle.

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Q1220. Can there be a Thread without a Process ?

Core Java

Ans. No.

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Q1221. Can we have an inner class within Interface ?

Core Java

Ans. Yes, we can define an inner class within interface.Inside the interface, the inner class is implicitly public static.

So the following is legit in Java

public interface BuggyBreadInterface {
   void doSomething();

   public class BuggyBreadClass implements BuggyBreadInterface{
      void doSomething(){
         System.out.println("Do something");
      }
   }
}

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Q1222. Is it a valid identifier in Java ?

int 123Abc = 5;

Core Java

Ans. No, identifier in java cannot start with a numeral.

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Q1223. What is the difference between Collections.emptyList() and creating new instance of List using new ?

Core Java

Ans. But Collections.emptyList() returns an Immutable list whereas new arraylist() creates a mutable list.

Advantage of getting an empty list using Collections.emptyList is that it returns a singleton list which can be shared among many references and hence made immutable. This is good fit for situations where we would like to initialize a list to basic minimum empty to avoid null pointer exception.

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Frequently asked Design Pattern interview question.

Q1224. What is a prototype design pattern ?

Design

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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Q1225. Write a Test Case using Mock ?

Testing

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?keyword=mock&category=code

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Very frequently asked.

Q1226. What is the use of synchronized keyword ?

Core Java

Ans. Synchronize is used to achieve mutual exclusion i.e at one time, the segment of the code, method that has been declared synchronized should be executed by single thread only and hence the lock needs to be retrieved before executing the segment and then released.

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Q1227. Write an SQL Statement to add a foreign key constraint in oracle ?

Database

Ans. ALTER TABLE <Table_Name> ADD CONSTRAINT <Constraint_Name> FOREIGN KEY (<Column_Name>) REFERENCES <Foreign_Table>(<Foreign_Column>);

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Q1228. How to Change Default Boot Kernel in Linux ?

Unix

Ans. https://www.redhat.com/archives/rhl-list/2005-April/msg04167.html

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Q1229. What is a Test Dependency Scope in Maven ?

Maven

Ans. This scope indicates that the dependency is not required for normal use of the application, and is only available for the test compilation and execution phases. This scope is not transitive.

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Q1230. What does the web status code 404,500 and 200 mean ?

Java EE

Ans. 404 means the resource is not found on the server.The resource might not be deployed correctly.

500 means internal server error which means that resource was located but then it resulted in some exception or error.

200 means Ok.

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