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Q191. How to configure second level cache in Hibernate ?

Ans. 1. Configure Provider class in Hibernate configuration file.

2. Add Cache usage tag ( read-only or read-write ) in mapping files ( hbm ).

3. Create an XML file called ehcache.xml and place in classpath which contains time settings and update settings, behavior of cache , lifetime and idletime of Pojos, how many objects are allowed.

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Q192. If I try to add Enum constants to a TreeSet, What sorting order will it use ?

Ans. Tree Set will sort the Values in the order in which Enum constants are declared.

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Q193. Can we override compareTo method for Enumerations ?

Core Java

Ans. No. compareTo method is declared final for the Enumerations and hence cannot be overriden. This has been intentionally done so that one cannot temper with the sorting order on the Enumeration which is the order in which Enum constants are declared.

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Q194. If you are given a choice to implement the code to either Insert a Record or Update if already exist, Which approach will you follow ?

1. Insert into the DB Table. If exception occurs, update the existing record.
2. Check if the record exists and update it if it exists, If not insert a new record.

Solution

Ans. In first case, there would be 2 DB calls in worst case and 1 in best case. In 2nd approach there will be always 2 DB calls.

Decision on the approach should depend on the following considerations -

1. How costly is the call to DB ? Are we using indices , hibernate etc

If calls to DB are costly , 1st approach should be the choice.

2. Exception Book keeping load upon exception.

The benefit of saving 1st call in approach 1 should be bigger than the Book keeping for the exception.

3. Probability of the exception in first apparoach.

If the DB Table is almost empty, it makes sense to follow Approach 1 as majority of the 1st calls will pass through without exception.

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Very Frequently asked.

Q195. Explain throw, throws , try and catch in Java ?

Core Java

Ans. throw is used to re throw an exception.throws is used to declare that the method throws the respective exceptions.try block is used to identify if the respective block has thrown any exception.catch is used to catch the exception that has been thrown by the respective try block.

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Q196. What is a transitive dependency ? Can we override Transitive Dependency version and If Yes, how ?

Maven

Ans. Transitive dependency is the dependencies not defined directly in the current POM but the POM of the dependent projects.

Yes we can override transitive dependency version by specifying the dependency in the current POM.

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Usually asked to experienced developers.

Q197. What is a cyclic dependency ?

Maven

Ans. A has dependency of B, B has dependency of C and C has dependency of A

With Maven 2 , came transitive dependency wherein in above scenario, C will acts as a dependency of A as if this dependency has been defined directly in A but the negative side is that if it leads to cyclic dependency , it creates problems.

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Q198. What is ConcurrentModificationException ?

Core Java

Ans. This is the exception that is thrown when we try to modify the non concurrent collection class while iterating through it.

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Q199. Difference between jar , war and ear ?

Java EE

Ans. Jar is Java Archieve i.e compressed Class or Class / Java files.

War comprises of compressed Servlet class files,JSP FIles,supporting files, GIF and HTML files.

Ear comprise of compressed Java and web module files ( was files ).

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Q200. What is the use of @GeneratedValue annotation in Hibernate?

Hibernate

Ans. This annotation is added to the auto increment column with the strategy to increment the column value. Usually this is added to the surrogate primary key column and specified with the Database Sequence.

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Q201. What is the use of runnable interface if we can always create a new thread using Thread class ?

Core Java

Ans. It's a choice to be made whether to use first approach ( Thread class ) or second approach ( runnable interface ) by the programmer. The second facility has been given for cases where your class is already extending some parent class and hence cannot extend another class ( for Thread ) as Java doesn't allow multiple inheritance.

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Q202. What is a BlockingQueue?

Data Structures

Ans. BlockingQueue is a Queue that supports operations that wait for the queue to become non-empty when retrieving and removing an element, and wait for space to become available in the queue when adding an element.

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Q203. Which of the following collections stores its elements in insertion Order ?

a. HashMap
b. TreeMap
c. LinkedHashMap
d. LinkedMap

Core Java

Ans. LinkedHashMap

Sample Code for LinkedHashMap

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Q204. In what order the elements of a HashSet are retrieved ?

a. Random Order
b. Insertion Order
c. Natural Sorting Order
d. Inverse Natural Sorting Order

Core Java

Ans. Random Order

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Q205. Which of the following is not the advantage of Mocking frameworks ?

a. It helps testing the module independently
b. It helps in faster unit testing
c. It helps in testing code even when external dependencies like service calls are not working
d. It helps in doing end to end Integration Testing

Ans. It helps in doing end to end Integration Testing

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Q206. Which of the following file is called deployment descriptor ?

a. application.xml
b. project.xml
c. web.xml
d. build.xml

Java EE

Ans. web.xml

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Q207. Which of the following is false about Constructors ?

a. Constructor can be overloaded
b. A no argument constructor is provided by the compiler if we declare only constructors with arguments.
c. Constructors shouldn't have any return types , not even void.
d. If super is not explicitly called, still super() is intrinsically added by the compiler.

Core Java

Ans. A no argument constructor is provided by the compiler if we declare only constructors with arguments.

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Q208. Which of the following doesn't extend Collection interface ?

a. Set
b. List
c. Map
d. Queue

Core Java

Ans. Map

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Q209. Which of the following Java feature promotes Code Re usability ?

a. Abstraction
b. Encapsulation
c. Inheritance
d. Polymorphism

Core Java

Ans. Inheritance

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Q210. Which of the following is not a build tool or plugin ?

a. Maven
b. Ant
c. Gradle
d. svn

Tool

Ans. svn

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Q211. What will happen if we don't have termination statement in recursion ?

Ans. Function call allocates a stackframe in stack. Every stackframe will use some memory to store local variables, parameters and to remember return address. Without terminating condition stackframes will keep consuming memory from stack and eventually program will result in stackoverflow error.

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Q212. In which cases , moving methods to utility class could be useful ?

Core Java

Ans. It could be worthy to move a method to util class if the method needs to be shared, doesn't require polymorphic behavior and need not be overridden in special cases.

Don't belong to one group through is-a relationship ( You can share through parent class method )

Don't implement a specific interface ( java 8 default methods )

Doesn't involve complex computing as you will be loosing the benefit of object state with just static method.

Doesn't require polymorphic behavior as static methods don't participate in runtime polymorphism.

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This question can be asked in different variants like performace improvement of an application, improving performance for DB communication etc.

Q213. 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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Q214. Difference between GET and POST Requests ?

Web Service

Ans. GET is supposed to get information from the server. Client sends the minimal information so that Server can respond with the response body on basis of request. For example - You want to get complete employment record for employee id 123

POST is supposed to send the information for submission. Payload or a Body is usually sent so that it can be persisted on the server. For example - Sending the complete information of an employee ( id, name , dept etc ) to the server for persisting it.

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Q215. 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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Q216. What is coupling and Cohesion ?

Design

Ans. Coupling is the degree of interdependence between software modules, a measure of how closely connected two modules are or the strength of the relationships between modules.

Cohesion refers to the degree to which the elements of a module belong together. Cohesion measures the strength of relationship between pieces of functionality within a given module.

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Q217. Design a Data Structure for a full text Search ?

Design

^{This question was recently asked at 'Myntra'.This question is still unanswered. Can you please provide an answer.}

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Q218. Write a Program to reverse a Linked List ?

Data Structure

^{This question was recently asked at 'Myntra,Compro Technologies'.This question is still unanswered. Can you please provide an answer.}

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Q219. Why java doesn't support multiple Inheritance ?

or

Explain Java Diamond Problem.

Core Java

Ans. class A {
void test() {
System.out.println("test() method");
}
}

class B {
void test() {
System.out.println("test() method");
}
}

Suppose if Java allows multiple inheritance like this,

class C extends A, B {
}

A and B test() methods are inheriting to C class.

So which test() method C class will take? As A & B class test() methods are different , So here we would Facing Ambiguity.

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Q220. Trim a string without using String library method

Core Java

^{This question was recently asked at 'Ariba'.This question is still unanswered. Can you please provide an answer.}

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