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Q361. Write a method to check if input String is Palindrome?

Ans. private static boolean isPalindrome(String str) {

if (str == null)
return false;

StringBuilder strBuilder = new StringBuilder(str);

strBuilder.reverse();

return strBuilder.toString().equals(str);

}

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Q362. Write a method that will remove given character from the String?

Core Java

Ans.

private static String removeChar(String str, char c) {    

   if (str == null)        

      return null;     

   

   return str.replaceAll(Character.toString(c), "");

}

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Q363. Why String is popular HashMap key in Java?

Core Java

Ans. Since String is immutable, its hashcode is cached at the time of creation and it doesnt need to be calculated again. This makes it a great candidate for key in a Map and its processing is fast than other HashMap key objects. This is why String is mostly used Object as HashMap keys.

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Q364. What does String intern() method do?

Core Java

Ans. intern() method keeps the string in an internal cache that is usually not garbage collected.

Moreover provide reference for scp object for corresponding string object present in heap memory.

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Q365. Will the following program display ""Buggy Bread"" ?

class Test{
   static void display(){
      System.out.println(""Buggy Bread"");
   }
}

class Demo{
   public static void main(String... args){
      Test t = null;
      t.display();
   }
}

Core Java

Ans. Yes. static method is not accessed by the instance of class. Either you call it by the class name or the reference.

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Q366. How substring() method of String class create memory leaks?

Core Java

Ans. substring method would build a new String object keeping a reference to the whole char array, to avoid copying it. Hence you can inadvertently keep a reference to a very big character array with just a one character string.

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Q367. 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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Q368. 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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Q369. 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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Q370. Difference between ArrayList and LinkedList ?

Ans. LinkedList and ArrayList are two different implementations of the List interface. LinkedList implements it with a doubly-linked list. ArrayList implements it with a dynamically resizing array.

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Q371. 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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Q372. 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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Q373. 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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Q374. What will be the output of following code ?
class BuggyBread2 {
   private static int counter = 0;
   void BuggyBread2() {
      counter = 5;
   }

   BuggyBread2(int x){
      counter = x;
   }

   public static void main(String[] args) {
      BuggyBread2 bg = new BuggyBread2();
      System.out.println(counter);
   }
}

Core Java

Ans. Compile time error as it won't find the constructor matching BuggyBread2().
Compiler won't provide default no argument constructor as programmer has already defined one constructor.
Compiler will treat user defined BuggyBread2() as a method, as return type ( void ) has been specified for that.

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Q375. 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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Q376. 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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Q377. 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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Q378. 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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Q379. Will this code compile fine ?

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

Core Java

Ans. Yes.

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Q380. What are different types of dependency injections ?

Design

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

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Q381. Can we compose the Parent Class object like this ?

class BuggyBread1 extends BuggyBread2 {

private BuggyBread2 buggybread2;

public static void main(String[] args){
buggybread2 = new BuggyBread2();
}
}

Ans. Yes.

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Q382. 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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Q383. Which are the sorted collections ?

Core Java

Ans. TreeSet and TreeMap

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Q384. 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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Q385. 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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Q386. 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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Q387. 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 )

Q388. 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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Q389. 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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Q390. What are the Core Interfaces of Hibernate Framework ?

Hibernate

Ans. Configuration
SessionFactory
Session
Transaction
Query and Citeria

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