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Q1331. What will be the crontab to run a job every last day of month ?

Unix

Ans. 59 23 28-31 * * [ "$(date +%d -d tomorrow)" = "01" ] && job_name

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Q1332. Write a unix command to find top 10 files by size ?

Unix

Ans. du -a /var | sort -n -r | head -n 10

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Q1333. What are fields that gets displayed when you execute "Top" command and briefly explain each field ?

Unix

Ans. PID - process identification number is an identification number that is automatically assigned to each process when it is created

USER - User Name

PR - PR is the process actual priority

NI is the nice value, which is a user-space concept.

VIRT -Virtual Image (kb). The total amount of virtual memory used by the task.

RES - Resident size (kb). The non-swapped physical memory a task has used.

SHR - Shared Mem size (kb). The amount of shared memory used by a task.

S - Process Status. The status of the task which can be one of:

D = uninterruptible sleep
R = running
S = sleeping
T = traced or stopped
Z = zombie

%CPU - % CPU usage

%MEM - % MEM Usage

TIME - Total CPU time the task has used since it started.

COMMAND - Command which was used to execute the process

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Q1334. Is null a dataype ?

Core Java

Ans. It is special literal. It is neither keyword nor identifier.

Any reference in java that doesnt point to any object , gets assigned null i.e is a reference to null

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Q1335. Which method of String class is used to convert Boolean to String ?

Core Java

Ans. toString() is an overloaded method of String class that is used to convert many data types to String, Boolean being one of them.

toString(Boolean bool)

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Q1336. What are Collection Classes ?

Core Java

Ans. Collections in java is a framework of classes that provides an abstracted data structure to store and manipulate the group of objects. Each class is unique in the way it stores , search , sort and modify the elements.

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Q1337. Write a Program to print the positive and negative numbers separetly

Core Java

Ans. int[] arr = {1,-1,2,-3,3,-4,4,5,6,-5,-6,-7,-8,8,9,-9};
List positiveNumbers = new ArrayList<>();
List negativeNumbers = new ArrayList<>();
for(int i = 0; i < arr.length(); i ){
if(I < 0){
negativeNumbers.add(i);
} else {
positiveNumbers.add(i);
}
}

System.out.println("Positive Numbers:" + positiveNumbers);
System.out.println("Negative Numbers:" + negativeNumbers);

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Q1338. Explain some of the http status codes you know ?

Java EE

Ans. 500 is Internal Server Error

404 is resource not found

400 is Bad Request

403 is Forbidden

401 is Unauthorized

200 is OK

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Q1339. What is Spring Boot ?

Spring Boot

Ans. Spring Boot is Springs convention-over-configuration solution for creating stand-alone, production-grade Spring-based Applications.

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Q1340. What is Maven ?

Maven

Ans. Maven is a build automation tool used primarily for Java projects.

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Q1341. Difference between Maven and Ant ?

Maven

Ans. Ant is procedural, we need to provide information about what to do and when to do through code.

Maven is declarative, everything is defined in the pom file.

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Q1342. What could be the problems due to the usage of static methods and elements ?

Core Java

Ans. static methods and static elements are shared by all objects of a class and hence could create problem.

Static methods are not synchronized by default and hence could create problem when accessed through multiple threads. Static elements are shareable by class and hence state of one object could be altered by another object.

Some limitations with Unit testing as not all mocking framework facilitate mocking them. Power mock allows but Mockito doesn't

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Q1343. What is the advantage of using static final or constant variables in Java ?

Core Java

Ans. Better Control - If the value is being used at multiple locations , that can be controlled better from single place. Any change would only require making single change.

Meaning , Aliasing and Better Readability - Sometimes its easy to read the value by its meaning or alias ( 0 as ZERO or 0 as NEUTRAL_VALUE ).

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Q1344. What is serialVersionUID ?

Core Java

Ans. Everytime an object is serialized the java serialization mechanism automatically computes a hash value by passing the meta information for the class. This id is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization

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Q1345. 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)

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Q1346. How to make sure that only one instance is created in Singleton Pattern ?

Core Java

Ans. public class SingleTon {
private SingleTon() {
if (singleTon != null) {
throw new RuntimeException("cant not create the object");
}
}
public Object clone() throws CloneNotSupportedException {
throw new CloneNotSupportedException("can not be create");
}

static private volatile SingleTon singleTon;
public static SingleTon getInstance() {
SingleTon singleTon = this.sample;
if (singleTon == null) {
synchronized (this) {
singleTon = this.singleTon;
if (singleTon == null) {
singleTon = this.singleton = new SingleTon();
}
}
}
return singleTon;
}
}

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Q1347. Can we have an entity in hibernate without primary Key ?

Hibernate

Ans. No, Every entity in hibernate needs to have a key, either primary or composite.

If we dont have a primary key on table, there are various ways this problem can be countered.

1. By using composite key on entity ( make sure that the appropriate unique constraint in defined on columns in Database )

2. By mapping Id in entity to ROWID of table.

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Q1348. Provide an implementation for Producer / Consumer using threads.

Core Java

Ans. https://www.tutorialspoint.com/javaexamples/thread_procon.htm

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Q1349. 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.

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Q1350. What is purchase condition and reward in promotions ?

IBM WCS

Ans. Purchase condition is the condition that must be fulfilled before a promotion is applied and Reward is the benefit that is passed to customer.

For Example - If promotion is "Buy 2 Quantity of X, Get Y Free" , Purchase condition is inclusion of 2 qty of X in Cart. Reward in this case would be 1 qty of Y.

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Q1351. What is the difference between following code segments

1.

try {
for(int i=0;i<100;i++){
calculate(i);
}
} catch (Exception ex) {
System.out.println("Error while processing")
}

and

2.

for(int i=0;i<100;i++){
try {
calculate(i);
} catch (Exception ex) {
System.out.println("Error while processing")
}
}

Core Java

Ans. In first case the whole loop will terminate as soon as any exception happens in the method calculate ( assuming calculate method is not handling its exception and those are thrown back at the calling method )

In Second case exception will be caught for individual iteration and hence it wont break the loop and will continue for the next iteration.

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Q1352. What will be the output of following code

public class BuggyBread {
   static class A {
      A() {
         f();
      }

      public void f() {
         System.out.println("A ctor");
      }
   }

   static class B extends A {
      B() {
         f();
      }

      public void f() {
         System.out.println("B ctor");
      }
   }

   public static void main(String[] args) {
      B b = new B();
      b.f();
      A a = new A();
      a.f();
   }
}

Core Java

Ans. B ctor
B ctor
B ctor
A ctor
A ctor

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Q1353. What is the difference between ServletConfig and ServletContext ?

Java EE

Ans. http://www.java4s.com/java-servlet-tutorials/difference-between-servletconfig-and-servletcontext-in-java/

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Q1354. What steps are needed to create a new promotion type ?

IBM WCS

Ans. a. Create necessary lzx files( template , object definition and properties ), make config entries and then Build open Laszlo project ( for LOBTools ) so that new promotion type should be displayed in management center.

b. Create a new promotion type xsl ( promotion type template ) and then map it to the promotion type.

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Q1355. How can you check the status of an ORDER ?

IBM WCS

Ans. By querying the STATUS from the ORDERS table.

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Q1356. I want to collect email addresses of all Registered Users. Which table should I refer ?

IBM WCS

Ans. ADDRESS

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Q1357. How can i get to know all the active promotions without going to management center ?

IBM WCS

Ans. We can query the DB as follows

Select NAME from PX_PROMOTION where STATUS=1;

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Q1358. How can we remove a JSP page from getting cached ?

IBM WCS

Ans. Remove the jsp entry from cachespec.xml.

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Q1359. Where do we store DB configuration and how can we change that ?

IBM WCS

Ans. wc-server.xml stores the DB configuration. We can either change it manually or by using setdbtype command.

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Q1360. Which table holds the encrypted login password ?

IBM WCS

Ans. USERREG

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