Java Interview Questions

In this tutorial we will see about some basic Java programming questions asked in interview. Below are the list of few questions and along with solution.

• Reversing a String without reverse() function
• Add numbers from the given input
• Count no. of words in the line or paragraph
• Find Armstrong number or not
• Find Prime number or not

Reversing a String without reverse() function

public class StringReverse {
 
 public static void main(String[] args) {
  
  String str = "Java Discover";
  System.out.println("Input String : "+str);
  str = myReverseFunction(str);
  System.out.println("Reversed String : "+str);
 }
 
 /**
  * Need to reverse a String without reverse() function
  * @param str
  * @return
  */
 public static String myReverseFunction(String str){
  char[] chars = str.toCharArray();
  StringBuilder sb = new StringBuilder();
  for (int i=str.length()-1;i>=0;i--) {
   sb.append(chars[i]);
  }
  return sb.toString();
 }
}

OUTPUT:

Input String : Java Discover
Reversed String : revocsiD avaJ

Add numbers from the given input
 

public class AddNumerals {
 
 public static void main(String[] args) {
  int value = 1234;
  int output = addNumerals(value);
  System.out.println("INPUT : "+value);
  System.out.println("OUTPUT : "+output);
 }
 
 /**
  * Add numerals in the given param value
  * For example input=1234 then output should be 1+2+3+4=10
  * @param value
  * @return
  */
 public static int addNumerals(int value){
  int output = 0;
  while(value > 0){
   output += value%10;
   value = value/10;
  }  
  return output;
 }
}

OUTPUT:

INPUT : 1234
OUTPUT : 10

Count no. of words in the line or paragraph
 

public class CountWords {

 public static void main(String[] args) {
  String line = "The string tokenizer class allows an application to break a string into tokens";
  int noOfWords = countNoOfWordsInLine(line);
  System.out.println("Input : "+line);
  System.out.println("No Of Words : "+noOfWords);
 }
 
 /**
  * Count no. of words in a line or paragraph 
  * @param line
  * @return
  */
 public static int countNoOfWordsInLine(String line){
  int output = 0;
  StringTokenizer tok = new StringTokenizer(line);
  output = tok.countTokens();
  return output;
 }
}

OUTPUT:

Input : The string tokenizer class allows an application to break a string into tokens
No Of Words : 13

Find Armstrong number or not
 

public class ArmstrongOrNot {
 
 public static void main(String[] args) {
  long input = 54748;
  boolean flag = checkArmstringOrNot(input);
  if(flag){
   System.out.println(input+" is Armstrong number");
  }else{
   System.out.println(input+" is NOT Armstrong number");
  }  
 }
 
 /**
  * Check given number is Armstrong number or not
  * For example, 371 is an Armstrong number, since 3^3 + 7^3 + 1^3 = 371 
  * @param input
  * @return
  */
 public static boolean checkArmstringOrNot(long input){
  int output = 0;
  long tmp = input;
        int length = Long.toString(input).length();
        while(tmp != 0){
         long rem = tmp % 10;
            long tmp1 = 1;
            for(int i = 0; i < length ;i++){
             tmp1 *= rem;
            }
            output += tmp1;
            tmp = tmp/10;
        }
        if(input == output){
            return true;
        }
        return false;
 }
}

OUTPUT:

54748 is Armstrong number

Find Prime number or not
 

public class PrimeOrNot {

 public static void main(String[] args) {
  int input = 23;
  boolean flag = primeOrNot(input);
  if(flag){
   System.out.println(input+" is a Prime number");
  }else{
   System.out.println(input+" is NOT a Prime number");
  }
 }
 
 /**
  * Check whether given number is Prime or Not
  * @param input
  * @return
  */
 public static boolean primeOrNot(int input){
  for(int i=2;i<=input/2;i++){
   if(input%i == 0){
    return false;
   }
  }
  return true;
 }
}

OUTPUT:

23 is a Prime number

More questions will be added shortly.