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 Q31. Write a Program to find common words in 2 separate stringsCore Java
Ans. public class BuggyBread {
   public static void main(String args[]) {
       String str1 = "we are what we repeatedly Do excellence, then, is not an act but a haBit";
       String str2 = "we are what we repeatedly Do is";
       String[] str1Words = str1.split(" ");
       String[] str2Words = str2.split(" ");
      
       Set str1WordsSet = new HashSet();
      
       for(String word:str1Words){
          str1WordsSet.add(word);
       }
      
       for(String word:str2Words){
          if(str1WordsSet.contains(word)){
             System.out.println(word);
          }
       }
      
   }
}

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   Like         Discuss         Correct / Improve     String  coding  code

 Q32. Write a Program to only print characters that have occured more than once in a StringCore Java
Ans. public class BuggyBread{
public static void main (String args[]) {
Set<Character> set = new HashSet();
Set<Character> setWithDuplicateChar = new HashSet();
String str = "hello world";
for(char character: str.toCharArray()){
if(set.contains(character)){
setWithDuplicateChar.add(character);
} else {
set.add(character);
}
}

System.out.println(setWithDuplicateChar);
}
}

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   Like         Discuss         Correct / Improve     String  Code  Coding

 Q33. Write a Program to print count of each character in a String.Core Java
Ans. public class BuggyBread {
public static void main(String args[]) {
Map<Character, Integer> countMap = new HashMap();
String str = "hello world";
for (char character : str.toCharArray()) {
if (countMap.containsKey(character)) {
countMap.put(character, countMap.get(character) + 1);
} else {
countMap.put(character, 1);
}
}
System.out.println(countMap);
}
}

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 Q34. Write a program to print the index of the first non repeated character in a java stringCore Java
Ans. public class BuggyBread1{
public static void main (String args[]) {
   String str = "hheello world";
   char[] charArray = str.toCharArray();
   char selectedChar = 'a';
   for(char char1: charArray){
      if(!str.contains(Character.toString(char1).concat(Character.toString(char1)))){
         selectedChar = char1;
         break;
      }
   }
   System.out.println(str.indexOf(Character.toString(selectedChar)));
}
}

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   Like         Discuss         Correct / Improve     string  code  coding     Asked in 9 Companies

 Q35. Write a Program to check if string is a Colidrome ?
(Colidrome is a word that has n alphabets followed by the reverse of the n alphabets, for ex - mallom) 		Core Java
Ans.
public class Class {
   public static void main(String[] args) {
      String str = "mallam";
      String firstHalf = str.substring(0, str.length() / 2);
      String secondHalf = str.substring(str.length() / 2);

      if (firstHalf.equals(new StringBuilder(secondHalf).reverse().toString())) {
         System.out.println("It's a Colidrome");
      } else {
         System.out.println("It's not a Colidrome");
      }
   }
}

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 Q36. Write a Program to check number of occurrences of one string within another ? Core Java
Ans. public class Class{
   public static void main(String[] args){
      String string1 = "Hello I am Jack. I live in United States. I live in california state.";

      String string2 = "I live in";

      int startIndex = 0;
      int endIndex = string1.length()-1;

      int countNoOfOccurences = 0;

      String remainingString = string1;

      while(startIndex < endIndex){
         if(remainingString.indexOf(string2) != -1){
            countNoOfOccurences++;
            startIndex = remainingString.indexOf(string2) + string2.length();
            remainingString = remainingString.substring(startIndex);
         } else {
            break;
         }
      }

      System.out.println(countNoOfOccurences);
   }
}

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 Q37. Write a program to check is a string is substring of another ?Core Java
Ans. public class Class{
   public static void main(String[] args){
      String string1 = "Hello I am Jack. I live in United States. I live in california state.";

      String string2 = "I live in";

      if(string1.indexOf(string2) >= -1){
         System.out.println("string2 is sub string of string1");
      } else {
         System.out.println("string2 is not sub string of string1");
      }
   }
}

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 Q38. How and Why Strings are interned in Java ?Core Java
Ans. String class has a public method intern() that returns a canonical representation for the string object. String class privately maintains a pool of strings, where String literals are automatically interned.

these are automatically interned so as to have efficient String comparison using == operator instead of equals which is usually slower.

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   Like         Discuss         Correct / Improve     string  string pool  string intern     Asked in 1 Companies

 Q39. Which memory segment holds String Pool in Java ?Core Java
Ans. String Pool resides in runtime constant Pool which is a part of Heap memory segment.

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 Q40. Trim a string without using String library methodCore Java
 This question was recently asked at 'Ariba'.This question is still unanswered. Can you please provide an answer.


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 Q41. 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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  Q42. 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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 Q43. How is String class unique ?Core Java
Ans. String class is immutable as well as final. Because of these properties , String objects offer many benefits

1. String Pool - When a string is created and if it exists in the pool, the reference of the existing string will be returned instead of creating a new object. If string is not immutable, changing the string with one reference will lead to the wrong value for the other references.

Example -

String str1 = "String1";
String str2 = "String1"; // It doesnt create a new String and rather reuses the string literal from pool

// Now both str1 and str2 pointing to same string object in pool, changing str1 will change it for str2 too

2. To Cache its Hashcode - If string is not immutable, One can change its hashcode and hence its not fit to be cached.

3. Security - String is widely used as parameter for many java classes, e.g. network connection, opening files, etc. Making it mutable might possess threats due to interception by the other code segment.

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 Q44. Are Strings objects in Java ?Core Java
Ans. Yes, everything except primitive types are objects in Java.

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 Q45. How does the String Class stores the string in memory ?Core Java
Ans. It stores the string as a character array with 2 bytes for each character.

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Very frequently asked. Among first few questions in almost all interviews. Among Top 5 frequently asked questions. Frequently asked in Indian service companies (HCL,TCS,Infosys,Capgemini etc based on multiple feedback ) and Epam Systems
  Q46. Difference between == and .equals() ?Core Java
Ans. "equals" is the method of object class which is supposed to be overridden to check object equality, whereas "==" operator evaluate to see if the object handlers on the left and right are pointing to the same object in memory.

x.equals(y) means the references x and y are holding objects that are equal. x==y means that the references x and y have same object.

Sample code:

String x = new String("str");
String y = new String("str");

System.out.println(x == y); // prints false
System.out.println(x.equals(y)); // prints true

  Sample Code for equals

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 Q47. Which String class does not override the equals() and hashCode() methods, inheriting them directly from class Object?Core Java
Ans. java.lang.StringBuffer.

  Sample Code for StringBuffer

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 Q48. What will this code print ?

String a = new String ("TEST");
String b = new String ("TEST");
if(a == b) {
System.out.println ("TRUE");
} else {
System.out.println ("FALSE");
}		Core Java
Ans. FALSE. == operator compares object references, a and b are references to two different objects, hence the FALSE. .equals method is used to compare string object content.

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Frequently asked in Infosys India
  Q49. What is a String Pool ?Core Java
Ans. String pool (String intern pool) is a special storage area in Java heap. When a string is created and if the string already exists in the pool, the reference of the existing string will be returned, instead of creating a new object and returning its reference.

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Advanced level question. Frequently asked in High end product companies. Frequently asked in Google , Cognizant and Deloitte ( Based on 2 feedback )
  Q50. Why is String immutable in Java ?Core Java
Ans. 1. String Pool - When a string is created and if it exists in the pool, the reference of the existing string will be returned instead of creating a new object. If string is not immutable, changing the string with one reference will lead to the wrong value for the other references.

Example -

String str1 = "String1";
String str2 = "String1"; // It doesn't create a new String and rather reuses the string literal from pool

// Now both str1 and str2 pointing to same string object in pool, changing str1 will change it for str2 too

2. To Cache its Hashcode - If string is not immutable, One can change its hashcode and hence it's not fit to be cached.

3. Security - String is widely used as parameter for many java classes, e.g. network connection, opening files, etc. Making it mutable might possess threats due to interception by the other code segment.

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Very frequently asked. Usually asked in different variants like Diff between StringBuffer , String Builder ; Difference between StringBuilder and String class; Choice between these classes etc.
  Q51. What is the difference between StringBuffer and String class ?Core Java
Ans. A string buffer implements a mutable sequence of characters. A string buffer is like a String, but can be modified. At any point in time it contains some particular sequence of characters, but the length and content of the sequence can be changed through certain method calls.

The String class represents character strings. All string literals in Java programs, such as "abc" are constant and implemented as instances of this class; their values cannot be changed after they are created.

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 Q52.  What is the role of JSON.stringify ?Json
Ans.  JSON.stringify() turns an object into a JSON text and stores that JSON text in a string. 

So If we stringfy above notation , it will become

{"name":"xyz","gender":"male";"age":30}

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Very Frequently asked. Usually asked along with String Class related questions.
  Q53. What is an immutable class ?Core Java
Ans. Class using which only immutable (objects that cannot be changed after initialization) objects can be created.

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Very frequently asked. Usually difference between String,StringBuffer and StringBuilder is asked in different variations.
  Q54. Difference between StringBuffer and StringBuilder ?Core Java
Ans. StringBuffer is synchronized whereas StringBuilder is not.

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Very frequently asked in different variations. Frequently asked in Deloitte ( 2 feedback ) , HCL Tech ( 3 feedback ), TCS and Coginizant (CTS)
  Q55. Explain the scenerios to choose between String , StringBuilder and StringBuffer ?

or

What is the difference between String , StringBuilder and StringBuffer ? 		Core Java
Ans. If the Object value will not change, use String Class because a String object is immutable.

If the Object value can change and will only be modified from a single thread, use StringBuilder because StringBuilder is unsynchronized(means faster).

If the Object value may change, and can be modified by multiple threads, use a StringBuffer because StringBuffer is thread safe(synchronized).

  Sample Code for String

  Sample Code for StringBuffer

  Sample Code for StringBuilder

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 Q56. What are different ways to create String Object? Explain.Core Java
Ans. There are total six ways

1. literals

When we create a String using double quotes, JVM looks in the String pool to find if any other String is stored with same value. If found, it just returns the reference to that String object else it creates a new String object with given value and stores it in the String pool.

2. new keyword

When we use new operator, JVM creates the String object but dont store it into the String Pool. We can use intern() method to store the String object into String pool or return the reference if there is already a String with equal value present in the pool.

3. string buffer
4. string builder
5. System.out.println
6. char to string




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  Q57. Write a method to check if input String is Palindrome?Core Java
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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 Q58. 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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 Q59. Which String class methods are used to make string upper case or lower case?Core Java
Ans. toUpperCase and toLowerCase

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 Q60. How to convert String to byte array and vice versa?Core Java
Ans. We can use String getBytes() method to convert String to byte array and we can use String constructor new String(byte[] arr) to convert byte array to String.

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