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Interview Questions and Answers - Order By Rating

Q2401. What is Dirty read in Database Transactions ?

Ans. A dirty read occurs when a transaction is allowed to read data from a row that has been modified by another running transaction but not yet committed.

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Q2402. What are the advantages disadvantages of keeping config entries in database instead of property file and vice versa ?

Design

Ans. Entries in DB will be retrieved at runtime unless a cache is maintained in application. Entries in File will be loaded to memory by default. Both can be implemented in 1 manner or other. By default property file will take space in memory, will be faster, and will require application restart on change. By Default DB config will be pulled at runtime, will be little slower, and doesn't require an application restart.

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Q2403. If Project A is calling web service of project B and there are some changes in project B, Will Project A needs to be rebuilt ?

Maven

Ans. That depends if the interface for the resource in Project B gets changed. If only the internal implementation is changed, No change is required in Project A. Project A is not even required to be rebuilt.

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Q2404. 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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Q2405. 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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Q2406. How do you resolve Maven Dependencies issue while upgrading dependencies versions ?

Maven

Ans. Step 1 - Upgrade the required dependency , perform build and check build errors

Step 2.1 - If the error is of missing transitive dependency ( which is rare and means that the previous version has a dependency which is missing in the later version ), I would look for the dependency in google and hence will include it as direct dependency in Pom file.

Step 2.2. If the error is for Duplicate dependencies , and the choice is between transitive and direct dependency, I usually remove the direct dependency.

Step 2.3 - If the error is for Duplicate dependencies , and both are transitive dependencies. I first make a choice ( usually later version ) and then ignore the previous version dependency.

Step 2.4 - If the error is for Duplicate dependencies , and there are more than 2 duplicates, I usually ignore it by specifying within maven-enforcer-plugin config.

Step 3 - Perform a Clean Build.

Step 4 - Check Maven Dependency Tree to make sure that Duplicates have been removed or dependency is there in case of missing dependency.

Step 5 - Perform tests and make sure that there are no runtime problems.

Step 6 - If there are runtime problems ( which very likely occurs if you have different version dependencies , very likely by doing 2.4 , you will have to remove step 2.4 and alternately perform 2.2 or 2.3 )

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Q2407. 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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Q2408. 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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Basic and Very Frequently asked.

Q2409. What is Polymorphism in Java ?

Core Java

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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Very frequently asked.

Q2410. 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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Q2411. Write a Test Case using Mock ?

Testing

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

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Frequently asked to fresh graduates.

Q2412. What is ACID ?

Database

Ans. ACID stands for Atomicity, Consistency, Isolation, Durability is a set of properties of database transactions.

Atomicity means all or nothing. i.e parts of a transaction shouldn't commit if any one of them fails. Either the whole transaction should succeed or it should be complete rollback.

Consistency means that any transaction should lead database from one stabe state to another.

Isolation means that the execution of transaction results in a system state that would be obtained if transactions were executed serially.

Durability means that when a transaction is committed it forms the permanent state of database.

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Frequently asked Design Pattern interview question.

Q2413. 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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Frequently asked.

Q2414. When does the finally block gets executed ?

Core Java

Ans. A finally block of code always executes, whether or not an exception has occurred.The only time finally won't be called is if you call System.exit() or if the JVM crashes first.

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Q2415. 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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Q2416. 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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Q2417. 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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Q2418. How to Bulk upload the data into Oracle database?

Database

Ans. We can use external table feature of Oracle.

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Q2419. Write code for Binary tree traversal ?

Core Java

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

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Q2420. Design a Library system ?

Design

Ans. Following Tables can be created

ASSET - Entity Table With foreign key reference to Table AssetType

ASSET_TYPE - Entity Table specifying information related to Asset Type like Books, CDs etc.

MEMBER - Registration information for the member

MEMBERSHIP_TYPE - Membership Types provided by Library

MEMBERSHIP - Relation table with foreign key for MEMBER ,

MEMBERSHIP_TYPE

ASSET_ISSUE_LEDGER - Relationship between MEMBER and ASSET. This specify the issue of particular asset to a particular member.

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Q2421. Can you assign value to a static final type at runtime ?

Core Java

Ans. No

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Q2422. In case of a synchronized method, Does the method only gets locked or the whole object ?

Core Java

Ans. Just the method gets locked.

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Q2423. There is a Table Student having Student Id, Name and Total Marks. Can you please write an SQL that will display the maximum marks obtained by a student ?

Database

Ans. SELECT MARKS FROM STUDENT ORDER BY MARKS DESC LIMIT 1;

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Q2424. Can we have two beans with same class with different bean id in spring ?

Spring

Ans. Yes

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Q2425. What is an IP address ?

Java EE

Ans. An Internet Protocol address is a numerical label assigned to each device participating in a computer network.

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Q2426. How to count total number of tables in database ?

Database

Ans. SELECT COUNT(*) FROM information_schema.tables

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Very Frequently asked to fresh graduates and less experienced.

Q2427. What are the principle concepts of Object Oriented Programming ?

Core Java

Ans. Abstraction Polymorphism Inheritance Encapsulation

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Q2428. Have you heard about the external table feature of Oracle ?

Database

Ans. The external tables feature is a complement to existing SQL Loader functionality. It enables to access data in external sources as if it were in a table in the database. We have used it few times for replicating tables across different database systems.

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Q2429. 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?

Core Java

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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Q2430. What do you know about JQuery ?

Java EE

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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