Core Java - Interview Questions and Answers for 'Core Java' | Search Interview Question

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Q631. What are the different operators in Java ?

Core Java

Ans. && - AND
|| - OR
! - LOGICAL NOT

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Q632. Write a Program to check if a number is perfect or not

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
       int number = 7;
       boolean perfectNumber = true;
       for(int x=2;x<number;x++){
          if(number % x == 0){
             perfectNumber = false;
          }
       }

       if(perfectNumber){
          System.out.println("Perfect Number");
       } else {
          System.out.println("Not a Perfect Number");
       }
   }
}

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Q633. Write a Program to print all perfect numbers from 1 to 100

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
      for(int number=1;number < 100;number++){
          boolean perfectNumber = true;
          for(int x=2;x<number;x++){
             if(number % x == 0){
                perfectNumber = false;
             }
          }

          if(perfectNumber){
             System.out.println(number);
          }
       }
   }
}

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Q634. What is a method reference in Java ?

Core Java

Ans. Introduced with java 8 , Method References help us to point to methods by their name.

A method references is described using :: symbol

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Q635. Write a Program to print index of first capital character in a string.

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
       String str = "we are what we repeatedly do excellence, then, is not an Act but a habit";
       int count = 1;
       for(Character c: str.toCharArray()){
          if(Character.isUpperCase(c)){
             break;
          } else {
             count++;
          }
       }

       System.out.println(count);
   }
}

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Q636. Write a Program to count number of capital characters in a String

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
       String str = "We are what we repeatedly do excellence, then, is not an Act but a habit";
       int count = 0;
       for(Character c: str.toCharArray()){
          if(Character.isUpperCase(c)){
             count++;
          }
       }

       System.out.println(count);
   }
}

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Q637. Write a Program to count number of lower case characters in a String

Core Java

Ans. public class BuggyBread1 {
   public static void main(String args[]) {
       String str = "We are what we repeatedly do excellence, then, is not an Act but a habit";
       int count = 0;
       for(Character c: str.toCharArray()){
          if(Character.isLowerCase(c)){
             count++;
          }
       }

       System.out.println(count);
   }
}

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Q638. Write a Program to print first word with a capital character in a String

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
       String str = "we are what we repeatedly do excellence, then, is not an act but a haBit";
       String wordWithCaptalChar = "";

       for(String word:str.split(" ")){
          if(!word.equals(word.toLowerCase())){
             wordWithCaptalChar = word;
          }
       }

       System.out.println(wordWithCaptalChar);
   }
}

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Q639. Write a Program to print the word in a String starting with a capital character

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
       String str = "we are what we repeatedly Do excellence, then, is not an act but a haBit";
       String wordWithFirstCaptalChar = "";

       for(String word:str.split(" ")){
          if(Character.isUpperCase(word.charAt(0))){
             wordWithFirstCaptalChar = word;
          }
       }

       System.out.println(wordWithFirstCaptalChar);
   }
}

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Q640. Write a Program to count number of words in a String

Core Java

Ans. public class BuggyBread1 {
   public static void main(String args[]) {
       String str = "we are what we repeatedly Do excellence, then, is not an act but a haBit";

       System.out.println(str.split(" ").length);
   }
}

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Q641. Write a Program to print duplicate words in a String

Core Java

Ans. public class BuggyBread {
public static void main(String args[]) {
String str = "we are what we repeatedly Do excellence, then, is not an act but a haBit";
Set<String> words = new HashSet();
for(String word:str.split(" ")){
if(words.contains(word)){
System.out.println(word);
} else {
words.add(word);
}
}
}
}

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Q642. Write a Program to print words of a String starting with character w

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
       String str = "we are what we repeatedly Do excellence, then, is not an act but a haBit";
       for(String word:str.split(" ")){
          if(word.startsWith("w")){
             System.out.println(word);
          }
       }
   }
}

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Q643. Write a Program to print words of a String containing the specified String.

For example - Print all words having characters ha

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
       String str = "we are what we repeatedly Do excellence, then, is not an act but a haBit";
       for(String word:str.split(" ")){
          if(word.contains("ha")){
             System.out.println(word);
          }
       }
   }
}

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Q644. Write a Program to print words in a string having length greater than 2 and third characters being p

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
       String str = "we are what we repeatedly Do excellence, then, is not an act but a haBit";
       for(String word:str.split(" ")){
          if(word.length() > 2 && word.charAt(2) == 'p'){
             System.out.println(word);
          }
       }
   }
}

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Q645. Write a Program to print words of a String having length greater than 2 and ending with it

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
       String str = "we are what we repeatedly Do excellence, then, is not an act but a haBit";
       for(String word:str.split(" ")){
          if(word.length() > 2 && word.endsWith("it")){
             System.out.println(word);
          }
       }
   }
}

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Q646. Write code to find second largest number in an array of integers.

Core Java

Ans. int arr[]={1,3,5,6,4,8,9,2,10};
Arrays.sort();
System.out.println(arr[arr.length-1]);

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Q647. Write a Program to find common words in 2 separate strings

Core 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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Q648. Write a program to print count / no of common words in 2 separate strings

Core 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);
       }

       int commonWordsCount = 0;

       for(String word:str2Words){
          if(str1WordsSet.contains(word)){
             commonWordsCount++;
          }
       }

       System.out.println(commonWordsCount);
   }
}

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Q649. Write a Program to remove duplicate words from the String

Core Java

Ans.
public class BuggyBread {
public static void main(String args[]) {
String str = "we are what we repeatedly Do excellence, then, is not an act but a haBit";
Set<String> wordSet = new LinkedHashSet(); // Using Linked Hash Set as we would like to retrieve words in the insertion order

for(String word: str.split(" ")){
wordSet.add(word);
}

for(String word: wordSet){
System.out.print(word);
System.out.print(" ");
}
}
}

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Q650. Write a Program to display the words of a String in alpahbetical or Dictionary Order

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
       String str = "we are what we repeatedly do excellence then is not an act but a haBit";
       Set<String> wordSet = new TreeSet(); // Using Linked Hash Set as we would like to retrieve words in the insertion order

       for(String word: str.split(" ")){
          wordSet.add(word);
       }

       for(String word: wordSet){
          System.out.print(word);
          System.out.print(" ");
       }
   }
}

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Q651. Write a program to print sum of numbers between the start and end number

For example - Passing start number as 2 and end number as 10, it should print 2+3+4+5+6+7+8+9+10 = 54

Core Java

Ans.
public class BuggyBread {
   public static void main(String args[]) {
       System.out.println(sum(2,10));
   }

   private static int sum(int start,int end){
      if(start > end){
         return 0;
      } else {
         return start + sum(start+1,end);
      }
   }
}

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Q652. Write a program using Recursion to print multiplication of numbers between the start and end number

For example - Passing start number as 2 and end number as 10, it should print 2*3*4*5*6*7*8*9*10 = 3628800

Core Java

Ans.
public class BuggyBread {
   public static void main(String args[]) {
       System.out.println(multiply(2,5));
   }

   private static int multiply(int start,int end){
      if(start > end){
         return 1;
      } else {
         return start * multiply(start+1,end);
      }
   }
}

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Q653. Write a Program to display numbers between 2 numbers using recursion

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
       displayNumbersBetween(2,10);
   }

   private static void displayNumbersBetween(int start,int end){
      if(start > end){
         return ;
      } else {
         System.out.println(start);
         displayNumbersBetween(start+1,end);
      }
   }
}

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Q654. Write a Program to print asterix like following using Recursion

**
***
****
*****
******
*******
********
*********
**********

Program should set the start and end index and then display this accordingly. For example the above pattern is for displayNumbersBetween(2,10) and following is for displayNumbersBetween(5,7)

*****
******
*******

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
       displayNumbersBetween(5,7);
   }

   private static void displayNumbersBetween(int start,int end){
      if(start > end){
         return ;
      } else {
         for(int x=1;x<=start;x++){
            System.out.print("*");
         }
         System.out.println("");
         displayNumbersBetween(start+1,end);
      }
   }
}

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Q655. Write a Program to print pattern like following

*
**
***
****
*****
******
*******
********
*********
**********

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
      for(int x=1;x<=10;x++){
         for(int y=1;y<=x;y++){
            System.out.print("*");
         }

         System.out.println("");
      }
   }
}

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Q656. Write a Program to print pattern like following

*_**_***_****_*****_***************

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
      for(int x=1;x<=5;x++){
         for(int y=1;y<=x;y++){
            System.out.print("*");
         }

         System.out.print("_");
      }

      for(int x=5;x>=1;x--){
         for(int y=1;y<=x;y++){
            System.out.print("*");
         }

         System.out.print("");
      }
   }
}

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Q657. Write a Program to print numbers like following

1
12
123
1234
12345

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
      for(int x=1;x<=5;x++){
         for(int y=1;y<=x;y++){
            System.out.print(y);
         }

         System.out.println(" ");
      }
   }
}

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Q658. Write a Program to print numbers like following

1
22
333
4444
55555

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
      for(int x=1;x<=5;x++){
         for(int y=1;y<=x;y++){
            System.out.print(x);
         }

         System.out.println(" ");
      }
   }
}

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Q659. Difference between concurrentHashMap and HashTable ?

Core Java

Ans. HashTable locks the complete collection to provide synchronization whereas ConcurrentHashMap only locks segments to achieve synchronization and hence better efficient and faster.

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Q660. isnt the use of HashTable and ConcurrentHashMap the same, i.e providing synchronized map collection ?

Core Java

Ans. Yes, they both aim at providing synchronized access to the Map collection. The only difference is in their implementation. ConcurrentHashMap came after HashTable and hence technically more efficient as it doesn't lock the complete map while accessing it.

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