java programming questions that helped me during my interviews
how to generate a log file in java
import java.util.logging.Logger; import java.util.logging.FileHandler; import java.util.logging.SimpleFormatter; import java.io.IOException; class Log { public static void main(String[] args) { Logger logger = Logger.getLogger("MyLog"); FileHandler fh; try { // This block configure the logger with handler and formatter fh = new FileHandler("C:/Users/myworld/Desktop/MyLogFile.log"); logger.addHandler(fh); SimpleFormatter formatter = new SimpleFormatter(); fh.setFormatter(formatter); // the following statement is used to log any messages logger.info("My first log"); } catch (SecurityException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } logger.info("Hi How r u?"); } }how to check a email is valid or not
import java.util.*; class IsValidEmailAddress { public boolean isValidEmailAddress(String email) { String ePattern = "^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@((\\[[0-9]{1,3}\\.[0-9]{1,3}\\.[0-9]{1,3}\\.[0-9]{1,3}\\])|(([a-zA-Z\\-0-9]+\\.)+[a-zA-Z]{2,}))$"; java.util.regex.Pattern p = java.util.regex.Pattern.compile(ePattern); java.util.regex.Matcher m = p.matcher(email); return m.matches(); } public static void main(String[] args) { IsValidEmailAddress valid = new IsValidEmailAddress(); System.out.println(valid.isValidEmailAddress("abc@gmail.com")); } }
how to generate a guid
import java.util.UUID; public class UniqueIDTest { public static void main(String[] args) { UUID uniqueKey = UUID.randomUUID(); System.out.println (uniqueKey); } }how to validate a phone number
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import VerhoeffAlgorithm;
class ValidationRE
{
public Boolean phoneNumberValidation( String sPhoneNumber){
//regular expression pattern for mobile number
Pattern pattern = Pattern.compile("^[2-9]{2}[0-9]{8}$");
Matcher matcher = pattern.matcher(sPhoneNumber);
if (matcher.matches()) { return true;}
else {return false; }
}
how to validate aadhar number
public static boolean validateAadharNumber(String aadharNumber){
Pattern aadharPattern = Pattern.compile("\\d{12}");
boolean isValidAadhar = aadharPattern.matcher(aadharNumber).matches();
if(isValidAadhar){
isValidAadhar = VerhoeffAlgorithm.validateVerhoeff(aadharNumber);
}
return isValidAadhar;
}
}
how to generate first n prime numbers import java.util.Scanner; class PrimeNumberDemo { public static void main(String args[]) { int n; int status = 1; int num = 3; //For capturing the value of n Scanner scanner = new Scanner(System.in); System.out.println("Enter the value of n:"); //The entered value is stored in the var n n = scanner.nextInt(); if (n >= 1) { System.out.println("First "+n+" prime numbers are:"); //2 is a known prime number System.out.println(2); } for ( int i = 2 ; i <=n ; ) { for ( int j = 2 ; j <= Math.sqrt(num) ; j++ ) { if ( num%j == 0 ) { status = 0; break; } } if ( status != 0 ) { System.out.println(num); i++; } status = 1; num++; } } }how to generate String Recursive Reversal
public class StringRecursiveReversal { String reverse = ""; public String reverseString(String str){ if(str.length() == 1){ return str; } else { reverse += str.charAt(str.length()-1) +reverseString(str.substring(0,str.length()-1)); return reverse; } } public static void main(String a[]){ StringRecursiveReversal srr = new StringRecursiveReversal(); System.out.println("Result: "+srr.reverseString("Javatospring")); } }how to generate gcd of two numbers
import java.util.Scanner; class GCD { public static void main(String[] args) { Scanner sc = new Scanner(System.in); System.out.print("enter a :"); int a = sc.nextInt(); System.out.print("enter b :"); int b = sc.nextInt(); while (a != b) { if(a > b) { a = a-b; } } System.out.println("GCD : " + a); } }how to generate chron job
import java.util.Timer; import java.util.TimerTask; class MyTask extends TimerTask{ static int i =0; public MyTask(){ //Some stuffs } @Override public void run() { i++; System.out.println( i+" : Hi see you after 1 seconds"); } } public class CronJob{ public static void main(String[] args){ Timer t = new Timer(); MyTask mTask = new MyTask(); // This task is scheduled to run every 1 seconds t.scheduleAtFixedRate(mTask, 0, 1000); } }how to generate random password generator
import java.util.Random; public class passGen{ //Verison 1.0 private static final String dCase = "abcdefghijklmnopqrstuvwxyz"; private static final String uCase = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; private static final String sChar = "!@#$%^&*"; private static final String intChar = "0123456789"; private static Random r = new Random(); private static String pass = ""; public static void main (String[] args) { System.out.println ("Generating pass..."); while (pass.length () != 6){ int rPick = r.nextInt(4); if (rPick == 0){ int spot = r.nextInt(25); pass += dCase.charAt(spot); } else if (rPick == 1) { int spot = r.nextInt (25); pass += uCase.charAt(spot); } else if (rPick == 2) { int spot = r.nextInt (7); pass += sChar.charAt(spot); } else if (rPick == 3){ int spot = r.nextInt (9); pass += intChar.charAt (spot); } } System.out.println ("Generated Pass: " + pass); } }how to generate factorial
import java.util.Scanner; class Factorial { static int fact = 1; public static void main(String[] args) { Scanner sc = new Scanner( System.in); System.out.print("\nenter the number to find factorial: " ); { fact = fact *num; } System.out.println( fact); } }