Interview Questions and Answers for 'Ab' | Search Interview Question

Interview Questions and Answers - Order By Newest

Q211. With a Table employee having columns Id,Name,ManagerEmployeeId, Write a SQL to find the Manager with maximum number of employees ?

Database

Ans. Select Name from EMPLOYEE where ID in (Select ManagerEmployeeId from EMPLOYEE
Group By ManagerEmployeeId
order by count(Id)
LIMIT 1)

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve database sql Asked in 1 Companies}

Q212. When should we use Abstract classes ?

Core Java

Ans. Abstract classes provide a mechanism of interfacing ( using abstract method ) as well as inheritance ( extending abstract class ). So they should be used in place of interfaces in case there is some code ( methods ) or object body ( member elements ) that can be reused with inheritance.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve abstract classes Asked in 1 Companies}

Q213. What is a factory design pattern ?

Design

Ans. Factory Design Patterns is the pattern that recommends creation of separate Factory Object for creation of other object.

So its like saying - If you want to create an object of ClassA, Talk to FactoryObject ( which is an object of FactoryClass ). FactoryObject in itself encapsulates the inputs and logic required to make the decision regarding the creation and construction of object.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve design pattern factory design pattern Asked in 9 Companies}

Q214. Which environment variables do we need to set in order to run Java programs?

Core Java

Ans. PATH, CLASSPATH and JAVA_HOME

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve environment variables path classpath java_home Asked in 3 Companies basic frequent}

Q215. Which interface is responsible for transaction management in JDBC ?

Database

Ans. Connection Interface

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve jdbc}

Q216. What actions you take if there is an issue related to Database server ?

Support

Ans. We involve DBA and try to solve it through them. By the time they are solving it , we keep the stake holders informed regarding the progress.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve database database server production support}

Q217. 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.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve stored procedure exception handling}

Q218. What are the benefits of creating immutable objects ?

Core Java

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

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve immutable immutability objects Asked in 1 Companies Intermediate frequent}

Q219. Create a Table with 2 Columns and Insert a row into it

Database

Ans. CREATE TABLE TABLE_NAME (
ID NUMBER PRIMARY KEY,
NAME VARCHAR(50) NOT NULL,
);

INSERT INTO TABLE_NAME(ID, NAME) VALUES(1, "Abc");

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve ddl dml create table insert records into table Asked in 1 Companies}

Q220. Difference between concurrentHashMap and HashTable ?

Core Java

Ans. HashTable locks the complete collection to provide synchronization whereas ConcurrentHashMap only locks segments to achieve synchronization and hence better efficient and faster.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve concurrentHashMap HashTable Map Collections Asked in 2 Companies}

Q221. isnt the use of HashTable and ConcurrentHashMap the same, i.e providing synchronized map collection ?

Core Java

Ans. Yes, they both aim at providing synchronized access to the Map collection. The only difference is in their implementation. ConcurrentHashMap came after HashTable and hence technically more efficient as it doesn't lock the complete map while accessing it.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve HashTable ConcurrentHashMap map Collections}

Q222. Difference between Singleton and Factory Design Pattern ?

Design

Ans. Both are creational design patterns but singleton facilitates in creation and reuse of single object whereas Factory deals with creation of multiple objects.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Design pattern singleton factory singleton vs factory Asked in 4 Companies}

Q223. What are the methods to connect to database in Java ?

Database

Ans. JDBC ( Java Database Connectivity ),ODBC (Open Database Connectivity), Hibernate, JPA ( Java Persistence API ), JOOQ,MyBatis

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve database connection jdbc ORM Hibernate Asked in 1 Companies}

Q224. What are the core OOPs concepts ?

Core Java

Ans. Abstraction, Encapsulation, Polymorphism , Composition and Inheritance

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve core oops concepts Asked in 65 Companies basic frequent}

Q225. Write program to create a linked list and perform different operations on it.

Algorithm

Ans. import java.util.*;
class LinkedListSolution{
protected LinkedList list;
public LinkedListSolution(){
list = new LinkedList();
}
public Object pop() throws NoSuchElementException{
if(list.isEmpty())
throw new NoSuchElementException();
else
return list.removeFirst();
}
public void push(Object obj){
list.addFirst(obj);
}
public Object peek() throws NoSuchElementException{
if(list.isEmpty())
throw new NoSuchElementException();
else
return list.getFirst();
}
public boolean isEmpty(){
return list.isEmpty();
}
public String toString(){
return list.toString();
}
}
class TestStack{
public static void main(String args[]){
LinkedListSolution s = new LinkedListSolution();
s.push("First");
s.push("Second");
s.push("Third");
System.out.println("Top: " s.peek());
s.push("Fourth");
while(!(s.isEmpty()))
System.out.println(s.pop());
}
}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Linkedlist data structures algorithm Asked in 2 Companies basic}

Q226. write program to do matrix multiplication

Core Java

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

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Asked in 1 Companies}

Q227. Can the foreign key column have null values ?

Database

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

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Asked in 1 Companies}

Q228. Can we override abstract methods ?

Core Java

Ans. Abstract methods are the methods that need to be overridden in the derived class ( either as implementing method or again abstract method ) so it's not only allowed but its required to override abstract method in the derived class.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve overriding abstract methods overriding abstract methods}

Q229. Can we override an abstract method with abstract method in the derived class ?

Core Java

Ans. Yes, but in that case the derived class itself should be abstract. We cannot have an object of a class without definition for the method which has been declared abstract in the parent.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve overriding overriding abstract methods abstract methods}

Q230. What are the benefits of using Prepared statements ?

Database

Ans. 1. Precompilation , DB-side caching and reuse of same execution plan leads to overall faster execution.

2. Automatic prevention of SQL injection attacks by escaping special characters

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Prepared statements benefits of prepared statements Asked in 1 Companies}

Try 1 Question(s) Test

Q231. What are the benefits of using prepared statements ? Does that benefit extend only if similar prepared statements are used within a application or it extends even with multiple applications having similar prepared statement ?

Database

Ans. Prepared Statements helps in reuse of database execution plan which can be cached at Database level and hence helps achieving faster execution and performance. As cached ps objects are creating at Database level and not application level, the use and benefit extends across multiple applications.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Prepared statements benefits of prepared statements Asked in 1 Companies}

Try 1 Question(s) Test

Q232. Where the prepared Statement object creating - In Java application or DB ?

Database

Ans. Prepared Statement objects are created and cached at database level.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Prepared statements Asked in 1 Companies}

Try 1 Question(s) Test

Q233. Does null and empty value for a column in Table means same ?

Database

Ans. No.

Null value means that the value is yet to be assigned or need not be assigned whereas empty value means that the blank value has already been assigned once. Null is the default for the null able columns that hasn't be assigned any value.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve}

Q234. What do you make out of this error

org.hibernate.exception.ConstraintViolationException: could not insert: [<Entity>]
Caused by: java.sql.SQLIntegrityConstraintViolationException: ORA-00001: unique constraint (<Constraint Name>) violated

and how would you go about debugging it ?

Database

Ans. Application is unable to insert a record as it violates a unique constraint.

The exception states the constraint and Table can be located by the Entity mapping. So I will go to the DB and will first check to which all columns the unique constraint applies. And then I will go and check the code and logs to see how come the duplicate column values were attempted to be inserted when they were not supposed to be.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve ConstraintViolationException SQLIntegrityConstraintViolationException}

Q235. What are the different database constraint types ?

Database

Ans. Not Null
Unique
Primary Key
Foreign Key
Check Constraint

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Asked in 1 Companies}

Q236. What is a check database constraint ?

Database

Ans. Constraint specifies the values allowed in one or more columns of every row of a table.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve database constraint}

Q237. What is a unique constraint ?

Database

Ans. Unique constraint ensures that a columns or combination or columns are always unique in a table and hence doesn't allow null or duplicates to be entered for the column or combination of columns.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve unique constraint}

Q238. What is the relation between Primary Key, Unique and Not Null constraint ?

Database

Ans. Primary Key constraint means that the column(s) should be unique and doesn't allow null. So Primary key constraint implies unique and not null constraint too.

Unique constraint implies not null constraint too as allowing null would violate uniqueness on those columns.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve database constraint}

Q239. What is an optimistic locking ?

Database

Ans. It's the way for synchronization wherein we can store version information in the table , so that if the same entity is updated by two transactions, the last to commit changes is informed of the conflict, and does not override the other transaction's work.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve locking optimistic locking Synchronization}

Q240. What was the need of creating an abstract class in Java when we cannot instantiate an object of it ?

Core Java

Ans. The objective of an abstract class is to provide an interface as well as code reuse. Though we cannot instantiate an instance of abstract class but we can reuse the code by extending such a class. Moreover abstract class provides interfacing to outside components just like interfaces.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve abstract class}

Search Interview Questions

Help us and Others Improve. Please let us know the questions asked in any of your previous interview.