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

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Q301. Can we add duplicate keys in a HashMap ? What will happen if we attempt to add duplicate values ?

Ans. No, We cannot have duplicate keys in HashMap. If we attempt to do so , the previous value for the key is overwritten.

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Q302. What are different types of cookies ?

Java EE

Ans. Session cookies , which are deleted once the session is over.

Permanent cookies , which stays at client PC even if the session is disconnected.

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Q303. Can we have try and catch blocks within finally ?

Core Java

Ans. Yes, if we have a cleanup code that might throw an exception in the finally block, then we can have a try-catch block

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Q304. Will this code compile fine ?

ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(new File("newFile.txt")));

Core Java

Ans. Yes.

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Q305. What's wrong with this code ?

public static void main(String[] args) {
String regex = "(\\w+)*";
String s = "Java is a programming language.";

Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(s);
while (matcher.next()) {
System.out.println("The e-mail id is: " + matcher.group());
}
}

Core Java

Ans. matcher.find() should have been used instead of matcher.next() within while.

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Q306. Which are the sorted collections ?

Core Java

Ans. TreeSet and TreeMap

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Q307. What is the difference between these two approaches of creating singleton Class ?

//Double Checked Locking Code
public static Singleton createInstance() {
   if(singleton == null){
      synchronized(Singleton.class) {
         if(singleton == null) {
            singleton = new Singleton();
         }
      }
   }
   return singleton;
}

//Single checked locking code
public static Singleton createInstance() {
   synchronized(Singleton.class) {
      if(singleton == null) {
         singleton = new Singleton();
      }
   }
   return singleton;
}

Design

Ans. In First Case , Lock for the synchronized block will be received only if singleton == null whereas in second case every thread will acquire the lock before executing the code.
The problem of synchronization with singleton will only happen when the object has not be instantiated. Once instantiated , the check singleton == null will always generate true and the same object will be returned and hence no problem. First condition will make sure that synchronized access ( acquiring locks ) will only take place if the object has not been created so far.

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Very frequently asked Hibernate interview question. Frequently asked in TCS ( based on 2 feedback )

Q308. What are different types of associations in Hibernate ?

Hibernate

Ans. There are 4 types of associations in Hibernate

One to One
One to Many
Many to One
Many to Many

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Q309. What are the configuration files in Hibernate ?

Hibernate

Ans. hibernate.cfg.xml ( Main Configuration File )

and *.hbm.xml files ( Mapping Files )

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Very frequently asked if being interviewed for hibernate. Frequently asked in Tata Consultancy (TCS) and Overstock.com

Q310. Difference between load and get ?

Hibernate

Ans. If id doesnt exist in the DB load throws an exception whereas get returns null in that case.get makes the call to DB immediately whereas load makes the call to proxy.

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Q311. What is the way to rollback transaction if something goes wrong using hibernate API ?

Hibernate

Ans. We can have the code calling Hibernate API within try block and can have transaction.rollback within Catch.

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Q312. What are the restrictions for the entity classes ?

Hibernate

Ans. 1. Entity classes should have default constructor.

2. Entity classes should be declared non final.

3. All elements to be persisted should be declared private and should have public getters and setters in the Java Bean style.

4. All classes should have an ID that maps to Primary Key for the table.

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Q313. Does java allow implementation of multiple interfaces having Default methods with Same name and Signature ?

Core Java

Ans. No. Compilation error.

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Q314. What are Default Methods ?

Core Java

Ans. With Java 8, We can provide method definitions in the Interfaces that gets carried down the classes implementing that interface in case they are not overridden by the Class. Keyword "default" is used to mark the default method.

Sample Code for interface default

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Q315. Can we use static method definitions in Interfaces ?

Core Java

Ans. Yes, Effective Java 8.

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Q316. How can we test methods individually which are not visible or declared private ?

Ans. We can either increase their visibility and mark them with annotation @VisibleForTesting or can use reflection to individually test those methods.

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Q317. When does an application throw NullPointerException ?

Core Java

Ans. When it tries to access an object element or method using reference which is actually null.

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Q318. What will be the output of this code ?

Set mySet = new HashSet();
mySet.add("4567");
mySet.add("5678");
mySet.add("6789");
for(String s: mySet){
System.out.println(s);
}

Ans. It will print 4567,5678 and 6789 but Order cannot be predicted.

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Q319. What will be the output of this code ?

Set mySet = new HashSet();
mySet.add("4567");
mySet.add("5678");
mySet.add("6789");
System.out.println(s.get(0));

Ans. This will give compile time error as we cannot retrieve the element from a specified index using Set. Set doesn't maintain elements in any order.

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Q320. How to generate getters and setters automatically in eclipse ?

Eclipse

Ans. Right Click -> Source -> Generate Getters and Setters.

and it will open up a dialog wherein we can select the fields to generate Getters and Setters.

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Q321. What are the considerations to be made in case of loops in Java ?

Core Java

Ans. 1. It shouldn't result in infinite loop. Please make sure that you have a condition that will terminate the loop and that condition should be reached.

2. Make sure to use the break statement if you aspire to only look for something. Not using break will unnecessarily execute it till the end of for loop in some cases.

3. Similarly use continue to execute the loop with next iteration and bypass the rest of the code block if required.

4. Try to avoid multiple nesting of for loops. If it''s required, Make sure to use break and continue properly so as to avoid some unnecessary processing.

5. Make sure to use try catch within the loop and not outside the for loop if you expect it to continue if one of the iteration fails.

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Q322. How is Abstraction implemented in Java ?

Core Java

Ans. Abstraction is provided in Java by following ways -

Coding to the ( Interfaces / Abstract Classes ) or contracts

By Encapsulating details within classes and exposing the minimal Door ( few public methods )

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Q323. What are some different logging levels for log4j ?

Log4j

Ans. DEBUG
ERROR
ALL
WARN
INFO
FATAL
OFF
TRACE
TRACE_INT
WARN

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Not frequently asked as it was introduced with Java 8.

Q324. What is the use of Optional ?

Core Java

Ans. Optional is a good way to protect application from runtime nullPointerException in case the the absent value has been represented as null. So basically Optional class provides the type checking during compile time and hence will never result in NPE.

For ex -

List> intList = new ArrayList>();
intList.add(Optional.empty());
intList.add(Optional.of(new Employee("abc")));
intList.add(Optional.of(new Employee("xyz")));
intList.add(Optional.of(new Employee("123")));
System.out.println(intList.get(0).getName());

So Now , even when the first list element is empty, this code will never throw an NullPointerException.

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Q325. Can we generate Java Documentation using Export -> JavaDoc using a jar file ?

Eclipse

Ans. Yes, If the jar contains the source code. No, If it contains only classes.

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Rarely asked as it was introduced with Java 8.

Q326. Name few "Optional" classes introduced with Java 8 ?

Core Java

Ans. http://www.buggybread.com/2015/01/java-optional-classes-and-interfaces.html

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Q327. Name few File IO related classes and interfaces ?

Core Java

Ans. http://www.buggybread.com/2015/01/java-file-io-classes-and-interfaces.html

Sample Code for File

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Q328. What are the various ways in which build can be scheduled in Jenkins ?

Jenkins

Ans. Builds can be triggered by source code management commits.
Can be triggered after completion of other builds.
Can be scheduled to run at specified time ( crons )
Manual Build Requests

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Q329. Difference between Stack and Heap memory ?

Core Java

Ans. Stack memory areas is used to hold method and local variables while objects are always allocated memory in the heap. The heap memory is shared between multiple threads whereas Stack memory isn't.

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Q330. How to access a Web Element if there are many elements with the same XPath ?

Ans. By specifying the Index like

//button[@class='button'])[2]

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