1. Reverse a String public
class ReverseString
{
public static void main(String[] args)
{
String str = "Automation";
StringBuilder reversed = new
StringBuilder(str).reverse(); System.out.println(reversed);
}
}
2. Check for Palindrome
public class Palindrome
{
public static void main(String[] args)
{
String str = "madam";
String reversed = new StringBuilder(str).reverse().toString();
System.out.println(str.equals(reversed));
}
}
3. Fibonacci Series
public class Fibonacci
{
public static void main(String[] args)
{
int
n = 10, num1 = 0, num2 = 1;
System.out.print("Fibonacci Series:
" + num1 + ", " + num2);
for
(int i = 2; i < n; i++)
{
int
num3 = num1 + num2;
System.out.print(", " + num3);
num1 = num2;
num2
= num3;
}
}
}
4. Factorial of a Number
public class Factorial
{
public static void main(String[] args)
{
int num = 5, factorial = 1;
for (int i = 1; i <= num; i++)
{
factorial *= I ;
}
System.out.println(factorial);
}
}
5. Prime Number Check
public class PrimeCheck
{
public static void main(String[] args)
{
int
num = 11;
boolean isPrime = true;
for (int i = 2; i <= Math.sqrt(num);
i++)
{
if (num % i == 0)
{
isPrime = false;
break;
}
}
System.out.println(isPrime);
}
}
6. Count Vowels and Consonants
public class VowelConsonantCount
{
public static void main(String[] args)
{
String str = "Automation";
int vowels = 0, consonants = 0;
for
(char c : str.toCharArray())
{
if
("aeiouAEIOU".indexOf(c) != -1)
{
vowels++;
}
else if (Character.isLetter(c))
{
consonants++;
}
}
System.out.println("Vowels: " +
vowels + ", Consonants: " + consonants);
}
}
7. Sort an Array
import java.util.Arrays;
public class SortArray
{
public static void main(String[] args)
{
int[] arr = {5, 2, 8, 1, 3};
Arrays.sort(arr);
System.out.println(Arrays.toString(arr));
}
}
8. Merge Two Arrays
import java.util.Arrays;
public class MergeArrays
{
public static void main(String[] args)
{
int[] arr1 = {1, 3, 5};
int[] arr2 = {2, 4, 6};
int[] merged = new int[arr1.length +
arr2.length];
System.arraycopy(arr1, 0, merged, 0,
arr1.length);
System.arraycopy(arr2, 0, merged,
arr1.length, arr2.length); System.out.println(Arrays.toString(merged));
}
}
9. Find the Largest Element in an Array
public class LargestInArray
{
public static void main(String[] args)
{
int[] arr = {1, 3, 5, 7, 9};
int
largest = arr[0];
for (int num : arr)
{
if
(num > largest)
{
largest = num;
}
}
System.out.println(largest);
}
}
10. Remove Duplicates from an Array
import java.util.HashSet;
public class RemoveDuplicates
{
public static void main(String[] args)
{
int[] arr = {1, 2, 2, 3, 4, 4};
HashSet set = new HashSet<>();
for (int num : arr)
{
set.add(num);
}
System.out.println(set);
}
}
11. Check if a Number is Armstrong
public class ArmstrongNumber
{
public static void main(String[] args)
{
int
num = 153, sum = 0, temp = num;
while (temp != 0)
{
int
digit = temp % 10;
sum += Math.pow(digit, 3);
temp /= 10;
}
System.out.println(num == sum);
}
}
12. Reverse a Number
public class ReverseNumber
{
public static void main(String[] args)
{
int
num = 12345, reversed = 0;
while (num != 0)
{
reversed = reversed * 10 + num % 10; num /=
10;
}
System.out.println(reversed);
}
}
13. Calculate GCD of Two Numbers
public class GCD
{
public static void main(String[] args)
{
int a = 60, b = 48;
while (b != 0)
{
int
temp = b; b = a % b; a = temp;
}
System.out.println(a);
}
}
14. Check for Anagram
import java.util.Arrays;
public class AnagramCheck
{
public static void main(String[] args)
{
String str1 = "listen", str2 =
"silent";
char[] arr1 = str1.toCharArray();
char[] arr2 = str2.toCharArray();
Arrays.sort(arr1);
Arrays.sort(arr2);
System.out.println(Arrays.equals(arr1,
arr2));
}
}
15. Count the Number of Digits in a Number
public class CountDigits
{
public static void main(String[] args)
{
int
num = 12345;
int count = String.valueOf(num).length();
System.out.println(count);
}
}
16. Print the Prime Numbers in a Range
public class PrimeInRange
{
public static void main(String[] args)
{
int
start = 10, end = 50;
for (int num = start; num <= end; num++)
{
boolean isPrime = true;
for
(int i = 2; i <= Math.sqrt(num); i++)
{
if (num % i == 0)
{
isPrime = false; break;
}
}
if
(isPrime && num > 1)
{
System.out.print(num + " ");
}
}
}
}
17. Find the Second Largest Element in an Array
public class SecondLargest
{
public static void main(String[] args)
{
int[] arr = {12, 35, 1, 10, 34, 1};
int
first = Integer.MIN_VALUE, second = Integer.MIN_VALUE;
for (int num : arr)
{
if
(num > first)
{
second = first; first = num;
}
else
if (num > second && num != first)
{
second = num;
}
}
System.out.println(second);
}
}
18. Swap Two Numbers
public class SwapNumbers
{
public static void main(String[] args)
{
int
a = 5, b = 10;
a = a + b;
b = a - b;
a = a - b;
System.out.println("a: " + a +
", b: " + b);
}
}
19. Print the Pascal's Triangle
public class PascalsTriangle
{
public static void main(String[] args)
{
int rows = 5; for (int i = 0; i < rows;
i++)
{
int num = 1;
System.out.format("%" + (rows - i) *
2 + "s", "");
for
(int j = 0; j <= i; j++)
{
System.out.format("%4d", num);
num
= num * (i - j) / (j + 1);
}
System.out.println();
}
}
}
20. Find the Missing Number in an Array
public class MissingNumber
{
public static void main(String[] args)
{
int[] arr = {1, 2, 4, 5, 6};
int
n = arr.length + 1;
int
total = n * (n + 1) / 2;
for (int num : arr)
{
total - = num;
}
System.out.println(total);
}
}
21. Convert Decimal to Binary
public class DecimalToBinary
{
public static void main(String[] args)
{
int
num = 10;
String binary =
Integer.toBinaryString(num);
System.out.println(binary);
}
}
22. Check for Perfect Number
public class PerfectNumber
{
public static void main(String[] args)
{
int
num = 28, sum = 0;
for (int i = 1; i <= num / 2; i++)
{
if
(num % i == 0)
{
sum += i;
}
}
System.out.println(num == sum);
}
}
23. Implementing a Simple Calculator
import java.util.Scanner;
public class SimpleCalculator
{
public static void main(String[] args)
{
Scanner scanner = new Scanner(System.in);
System.out.print("Enter first number:
");
double num1 = scanner.nextDouble();
System.out.print("Enter second number:
");
double num2 = scanner.nextDouble();
System.out.print("Enter operation (+,
-, *, /): ");
char
operation = scanner.next().charAt(0);
double result;
switch (operation)
{
case
'+': result = num1 + num2;
break;
case '-':
result = num1 - num2;
break;
case '*':
result = num1 * num2;
break;
case '/':
result = num1 / num2;
break;
default:
throw new
IllegalArgumentException("Invalid operation");
}
System.out.println("Result: " +
result);
}
}
24. Find the Sum of Digits of a Number
public class SumOfDigits
{
public static void main(String[] args)
{
int
num = 12345, sum = 0;
while (num != 0)
{
sum += num % 10; num /= 10;
}
System.out.println(sum);
}
}
25. Find the Length of a String
public class StringLength {
public static void main(String[] args)
{
String str = "Automation";
System.out.println(str.length());
}
}
26. Check if a String is Empty
public class CheckEmptyString
{
public static void main(String[] args)
{
String str = "";
System.out.println(str.isEmpty());
}
}
27. Count the Occurrences of a Character in a String
public class CountCharacter
{
public static void main(String[] args)
{
String str = "Automation";
char ch = 'a';
int
count = 0;
for
(char c : str.toCharArray())
{
if (c == ch) count++;
}
System.out.println(count);
}
}
28. Find the First Non-Repeated Character in a String
import java.util.LinkedHashMap;
import java.util.Map;
public class FirstNonRepeatedCharacter
{
public static void main(String[] args)
{
String str = "swiss";
Map
charCount = new LinkedHashMap<>();
for
(char c : str.toCharArray())
{
charCount.put(c, charCount.getOrDefault(c,
0) + 1);
}
for (Map.Entry entry :
charCount.entrySet())
{
if
(entry.getValue() == 1)
{
System.out.println(entry.getKey());
break;
}
}
}
}
29. Remove All Whitespaces from a String
public class RemoveWhitespaces
{
public static void main(String[] args)
{
String str = " A u t o m a t i o n
";
String result =
str.replaceAll("\\s+", "");
System.out.println(result);
}
}
30. Find the Common Elements in Two Arrays
import java.util.HashSet;
public class CommonElements
{
public static void main(String[] args)
{
int[] arr1 = {1, 2, 3, 4};
int[] arr2 = {3, 4, 5, 6};
HashSet set = new HashSet<>();
for
(int num : arr1)
{
set.add(num);
}
for
(int num : arr2)
{
if
(set.contains(num))
{
System.out.print(num + " ");
}
}
}
}
31. Find the Factorial of a Number using Recursion
public class FactorialRecursion
{
public static void main(String[] args)
{
int
num = 5;
System.out.println(factorial(num));
}
static int factorial(int n)
{
if
(n == 0) return 1;
return n * factorial(n - 1);
}
}
32. Generate Random Numbers
import java.util.Random;
public class RandomNumbers
{
public static void main(String[] args)
{
Random random = new Random();
for
(int i = 0; i < 5; i++)
{
System.out.println(random.nextInt(100)); //
Random number between 0-99
}
}
}
33. Check if a Year is Leap Year
public class LeapYear
{
public static void main(String[] args)
{
int
year = 2024;
boolean isLeap = (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0); System.out.println(isLeap);
}
}
34. Find the Sum of First N Natural Numbers
public class SumOfNaturalNumbers
{
public static void main(String[] args)
{
int
n = 10, sum = n * (n + 1) / 2;
System.out.println(sum);
}
}
35. Implement a Simple Login System
import java.util.Scanner;
public class SimpleLogin
{
public static void main(String[] args)
{
String username = "admin";
String password = "password";
Scanner scanner = new Scanner(System.in);
System.out.print("Enter username:
");
String inputUsername = scanner.nextLine();
System.out.print("Enter password:
");
String inputPassword = scanner.nextLine();
if
(username.equals(inputUsername) && password.equals(inputPassword))
{
System.out.println("Login
successful!");
}
else
{
System.out.println("Login
failed!");
}
}
}
36. Check if a String Contains Another String
public class StringContains
{
public static void main(String[] args)
{
String str1 = "Automation
Testing";
String str2 = "Testing";
System.out.println(str1.contains(str2));
}
}
37. Find the Maximum Occurring Character in a String
import java.util.HashMap;
public class MaxOccurringCharacter
{
public static void main(String[] args)
{
String str = "programming";
HashMap charCount = new HashMap<>();
for (char c : str.toCharArray())
{
charCount.put(c, charCount.getOrDefault(c, 0)
+ 1);
}
char
maxChar = str.charAt(0);
int
maxCount = 0;
for
(char c : charCount.keySet())
{
if
(charCount.get(c) > maxCount)
{
maxCount = charCount.get(c);
maxChar = c;
}
}
System.out.println(maxChar);
}
}
38. Implementing Bubble Sort
public class BubbleSort
{
public static void main(String[] args)
{
int[] arr = {64, 34, 25, 12, 22, 11, 90};
int n = arr.length;
for
(int i = 0; i < n - 1; i++)
{
for (int j = 0; j < n - i - 1; j++)
{
if (arr[j] > arr[j + 1])
{
int
temp = arr[j];
arr[j] = arr[j + 1];
arr[j + 1] = temp;
}
}
}
for
(int num : arr)
{
System.out.print(num + " ");
}
}
}
39. Implementing Selection Sort
public class SelectionSort
{
public static void main(String[] args)
{
int[] arr = {64, 25, 12, 22, 11};
int
n = arr.length;
for
(int i = 0; i < n - 1; i++)
{
int
minIndex = i;
for
(int j = i + 1; j < n; j++)
{
if
(arr[j] < arr[minIndex])
{
minIndex = j;
}
}
int
temp = arr[minIndex];
arr[minIndex] = arr[i];
arr[i] = temp;
}
for
(int num : arr)
{
System.out.print(num + " ");
}
}
}
