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Very frequently asked in HCL Tech ( Based of 4 inputs )

Q211. Write a program to reverse a string iteratively and recursively ?

Core Java

Ans. Using String method -

new StringBuffer(str).reverse().toString();

Iterative -

public static String getReverseString(String str){
StringBuffer strBuffer = new StringBuffer(str.length);
for(int counter=str.length -1 ; counter>=0;counter--){
strBuffer.append(str.charAt(counter));
}
return strBuffer;
}

Recursive -

public static String getReverseString(String str){
if(str.length <= 1){
return str;
}
return (getReverseString(str.subString(1)) + str.charAt(0);
}

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Q212. Write a Program to check if 2 strings are Anagrams ?

Core Java

Ans. public void checkIfAnagram(String str1,String str2){
boolean anagram = true;
for(char c:str1.toCharArray()){
if(!str2.contains(String.valueOf(c))){
System.out.println("Strings are Anagrams");
anagram = false;
}

if(anagram == true){
System.out.println("Strings are not Anagrams");
}
}
}

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Q213. Difference between new operator and Class.forName().newInstance() ?

Ans. new operator is used to statically create an instance of object. newInstance() is used to create an object dynamically ( like if the class name needs to be picked from configuration file ). If you know what class needs to be initialized , new is the optimized way of instantiating Class.

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Q214. What are the pre-requisite for the collection to perform Binary Search ?

Ans. 1. Collection should have an index for random access.
2. Collection should have ordered elements.

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Q215. Which of the following syntax is correct ?import static java.lang.System.*;or static import java.lang.System.*;

Core Java

Ans. import static java.lang.System.*;

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Q216. What will be the output of following Code ?

class BuggyBread {
   public static void main(String[] args) {
      String s2 = "I am unique!";
      String s5 = "I am unique!";

      System.out.println(s2 == s5);
   }
}

Core Java

Ans. true, due to String Pool, both will point to a same String object.

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Q217. What are temp tables ?

Ans. These are the tables that are created temporarily and are deleted once the Stored Procedure is complete.

For example - we may like to pull some info from a table and then do some operations on that data and then store the output in final output table. We can store the intermediary values in a temp table and once we have final output with us, we can just delete it.

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Q218. 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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Q219. 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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Q220. What are different types of dependency injections ?

Design

Ans. Setter injection
Constructor injection
Interface injection
Look-up method/method injection

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Q221. 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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Q222. 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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Q223. What are the advantages of Hibernate ?

Hibernate

Ans. 1. No need to know SQL, RDBMS, and DB Schema.
2. Underlying Database can be changed without much effort by changing SQL dialect and DB connection.
3.Improved Performance by means of Caching.

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Q224. What is the purpose of dialect configured in Hibernate configuration file ?

Hibernate

Ans. It tells the framework which SQL varient to generate.

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Q225. Please specify in what sequence the objects of following classes will be created ?

Session , SessionFactory, Query , Configuration

Hibernate

Ans. Configuration -> SessionFactory -> Session -> Query

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

Q226. 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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Q227. 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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Q228. What are the Core Interfaces of Hibernate Framework ?

Hibernate

Ans. Configuration
SessionFactory
Session
Transaction
Query and Citeria

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Q229. What are collection types in Hibernate ?

Hibernate

Ans. Bag, Set , List , Array, Map

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

Q230. 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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Q231. 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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Q232. 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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Q233. 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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Q234. 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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Q235. Can we use static method definitions in Interfaces ?

Core Java

Ans. Yes, Effective Java 8.

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Q236. Difference between a Pointer and a Reference ?

Ans. We can't get the address of a reference like a pointer. Moreover we cannot perform pointer arithmetic with references.

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Q237. How to create a Junit to make sure that the tested method throws an exception ?

Ans. Using annotation Test with the argument as expected exception.

@Test (expected = Exception.class)

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Q238. 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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Q239. Why can't we use this in static context ?

Core Java

Ans. Static methods can be called using instance references wherein this would have made sense but static method can also be called using Class name wherein this would mean nothing and hence forbidden.

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Q240. 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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