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

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Q661. What access the variable gets if we don't provide any access specifier ?

Core Java

Ans. It gets the default access i.e package protected.

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Q662. How are the concept of Association related to Composition and Inheritance ?

Core Java

Ans. Composition and Inheritance are the different types of Associations for Classes.

Composition is a has-a association between classes.
Inheritance is a is-a association between classes.

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Q663. What are the core OOPs concepts ?

Core Java

Ans. Abstraction, Encapsulation, Polymorphism , Composition and Inheritance

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Q664. Write a method / program that will determine if the parenthesis are balanced in a given string.

Core Java

Ans. https://www.geeksforgeeks.org/check-for-balanced-parentheses-in-an-expression/

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Q665. Why is it important to close files and streams ?

Core Java

Ans. Optimizing Resource utilization. When you open a file using any programming language , that is actually a request to operating system to access the file. When such a request is made , resources are allocated by the OS. When you gracefully close those files, those resources are set free.

In Java if you don’t close the streams and files, Garbage collection identifies the open files which have lost the reference and hence will close them.

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Q666. What is the difference between && and & in Java ?

Core Java

Ans. && is a Logical whereas & is a bitwise operator

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Q667. Why don't Java objects have destructors ?

Core Java

Ans. Java manages memory using built-in garbage collector

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Q668. Write a Java program to print 10 random numbers between 1 to 100?

Core Java

^{This question was recently asked at 'karya technology'.This question is still unanswered. Can you please provide an answer.}

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Q669. How to find the median number in an array of integers ?

Core Java

Ans.

Arrays.sort(numArray);
double median;
if (numArray.length % 2 == 0)
median = ((double)numArray[numArray.length/2] (double)numArray[numArray.length/2 - 1])/2;
else
median = (double) numArray[numArray.length-1/2];

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Q670. Write a Program to find the missing integer in an array of consecutive numbers?

Core Java

^{This question was recently asked at 'Knight Capital'.This question is still unanswered. Can you please provide an answer.}

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Q671. Write a Program to validate if a particular character occurs after another in a string

Core Java

Ans. public class Class{
   public static void main(String[] args){
      String str = "xyz123.co@m";

      if(str.indexOf('.') < str.indexOf('@')){
         System.out.println("Not a Valid Email Address");
      }
   }
}

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Q672. Write a Program to validate an email address

Core Java

Ans. public class Class{
public static void main(String[] args){
String str = "xyz@123.com";

if(!str.contains("@") && !str.contains(".") && (str.indexOf('.') < str.indexOf('@'))){
System.out.println("Not a Valid Email Address");
}
}
}

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Q673. Upon compiling the following class, What .class files will get created

public class OuterClass{
class InnerClass{
}
}

Core Java

Ans. OuterClass.class AND OuterClass$InnerClass.class

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Q674. 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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Q675. 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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Q676. 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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Q677. 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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Q678. 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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Q679. 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.println("");
      }

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

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

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Q680. 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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Q681. 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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Q682. 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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Q683. 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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Q684. 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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Q685. Write a Program to print factorial of a number using recursion

Core Java

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

private static int factorial(int number){
if(number == 1){
return 1;
} else {
return number * factorial(number - 1);
}
}
}

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Q686. 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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Q687. 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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Q688. 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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Q689. 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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Q690. 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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