Important Java Programs

title: Important Programs description: Java ke most important programs jo har jagah pooche jaate hain

1. Fibonacci Series

// Iterative void fibonacci(int n) { int a = 0, b = 1; System.out.print(a + " " + b + " "); for (int i = 2; i < n; i++) { int c = a + b; System.out.print(c + " "); a = b; b = c; } }

2. Prime Number Check

boolean isPrime(int n) { if (n < 2) return false; for (int i = 2; i * i <= n; i++) if (n % i == 0) return false; return true; }

3. Palindrome Check (String)

boolean isPalindrome(String s) { int l = 0, r = s.length() - 1; while (l < r) { if (s.charAt(l) != s.charAt(r)) return false; l++; r--; } return true; }

4. Reverse a Number

java exampleWoHoTech

int reverseNumber(int n) {
    int rev = 0;
    while (n != 0) {
        rev = rev * 10 + n % 10;
        n /= 10;
    }
    return rev;
}

5. Armstrong Number

java exampleWoHoTech

boolean isArmstrong(int n) {
    int sum = 0, temp = n, digits = String.valueOf(n).length();
    while (temp != 0) {
        sum += Math.pow(temp % 10, digits);
        temp /= 10;
    }
    return sum == n;
}
// 153 = 1³ + 5³ + 3³ = 1 + 125 + 27 = 153 ✓

6. Factorial

long factorial(int n) { long result = 1; for (int i = 2; i <= n; i++) result *= i; return result; }

7. Array Reverse

void reverse(int[] arr) { int l = 0, r = arr.length - 1; while (l < r) { int t = arr[l]; arr[l] = arr[r]; arr[r] = t; l++; r--; } }

8. Find Max aur Min

void findMaxMin(int[] arr) { int max = arr[0], min = arr[0]; for (int n : arr) { if (n > max) max = n; if (n < min) min = n; } System.out.println("Max: " + max + ", Min: " + min); }

9. String Reverse

java exampleWoHoTech

String reverseString(String s) {
    return new StringBuilder(s).reverse().toString();
}

10. Anagram Check

java exampleWoHoTech

boolean isAnagram(String s1, String s2) {
    char[] a = s1.toLowerCase().toCharArray();
    char[] b = s2.toLowerCase().toCharArray();
    Arrays.sort(a); Arrays.sort(b);
    return Arrays.equals(a, b);
}

11. Duplicate Elements in Array

java exampleWoHoTech

void findDuplicates(int[] arr) {
    Set<Integer> seen = new HashSet<>();
    for (int n : arr)
        if (!seen.add(n)) System.out.println("Duplicate: " + n);
}

12. Count Characters in String

java exampleWoHoTech

Map<Character, Integer> charCount(String s) {
    Map<Character, Integer> map = new LinkedHashMap<>();
    for (char c : s.toCharArray())
        map.put(c, map.getOrDefault(c, 0) + 1);
    return map;
}

13. Two Sum

int[] twoSum(int[] nums, int target) { Map<Integer, Integer> map = new HashMap<>(); for (int i = 0; i < nums.length; i++) { int comp = target - nums[i]; if (map.containsKey(comp)) return new int[]{map.get(comp), i}; map.put(nums[i], i); } return new int[]{}; }

14. Bubble Sort

void bubbleSort(int[] arr) { 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 t = arr[j]; arr[j] = arr[j+1]; arr[j+1] = t; } }

15. Binary Search

int binarySearch(int[] arr, int target) { int lo = 0, hi = arr.length - 1; while (lo <= hi) { int mid = lo + (hi - lo) / 2; if (arr[mid] == target) return mid; if (arr[mid] < target) lo = mid + 1; else hi = mid - 1; } return -1; }

16. Star Pattern

void triangle(int n) { for (int i = 1; i <= n; i++) { for (int j = 1; j <= i; j++) System.out.print("* "); System.out.println(); } }

17. Matrix Transpose

int[][] transpose(int[][] mat) { int n = mat.length; int[][] result = new int[n][n]; for (int i = 0; i < n; i++) for (int j = 0; j < n; j++) result[j][i] = mat[i][j]; return result; }

18. Linked List Reverse

java exampleWoHoTech

Node reverse(Node head) {
    Node prev = null, curr = head;
    while (curr != null) {
        Node next = curr.next;
        curr.next = prev;
        prev = curr;
        curr = next;
    }
    return prev;
}

title: Important Programs description: Java ke most important programs jo har jagah pooche jaate hain

1. Fibonacci Series

// Iterative void fibonacci(int n) { int a = 0, b = 1; System.out.print(a + " " + b + " "); for (int i = 2; i < n; i++) { int c = a + b; System.out.print(c + " "); a = b; b = c; } }

2. Prime Number Check

boolean isPrime(int n) { if (n < 2) return false; for (int i = 2; i * i <= n; i++) if (n % i == 0) return false; return true; }

3. Palindrome Check (String)

boolean isPalindrome(String s) { int l = 0, r = s.length() - 1; while (l < r) { if (s.charAt(l) != s.charAt(r)) return false; l++; r--; } return true; }

4. Reverse a Number

java exampleWoHoTech

int reverseNumber(int n) {
    int rev = 0;
    while (n != 0) {
        rev = rev * 10 + n % 10;
        n /= 10;
    }
    return rev;
}

5. Armstrong Number

java exampleWoHoTech

boolean isArmstrong(int n) {
    int sum = 0, temp = n, digits = String.valueOf(n).length();
    while (temp != 0) {
        sum += Math.pow(temp % 10, digits);
        temp /= 10;
    }
    return sum == n;
}
// 153 = 1³ + 5³ + 3³ = 1 + 125 + 27 = 153 ✓

6. Factorial

long factorial(int n) { long result = 1; for (int i = 2; i <= n; i++) result *= i; return result; }

7. Array Reverse

void reverse(int[] arr) { int l = 0, r = arr.length - 1; while (l < r) { int t = arr[l]; arr[l] = arr[r]; arr[r] = t; l++; r--; } }

8. Find Max aur Min

void findMaxMin(int[] arr) { int max = arr[0], min = arr[0]; for (int n : arr) { if (n > max) max = n; if (n < min) min = n; } System.out.println("Max: " + max + ", Min: " + min); }

9. String Reverse

java exampleWoHoTech

String reverseString(String s) {
    return new StringBuilder(s).reverse().toString();
}

10. Anagram Check

java exampleWoHoTech

boolean isAnagram(String s1, String s2) {
    char[] a = s1.toLowerCase().toCharArray();
    char[] b = s2.toLowerCase().toCharArray();
    Arrays.sort(a); Arrays.sort(b);
    return Arrays.equals(a, b);
}

11. Duplicate Elements in Array

java exampleWoHoTech

void findDuplicates(int[] arr) {
    Set<Integer> seen = new HashSet<>();
    for (int n : arr)
        if (!seen.add(n)) System.out.println("Duplicate: " + n);
}

12. Count Characters in String

java exampleWoHoTech

Map<Character, Integer> charCount(String s) {
    Map<Character, Integer> map = new LinkedHashMap<>();
    for (char c : s.toCharArray())
        map.put(c, map.getOrDefault(c, 0) + 1);
    return map;
}

13. Two Sum

14. Bubble Sort

void bubbleSort(int[] arr) { 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 t = arr[j]; arr[j] = arr[j+1]; arr[j+1] = t; } }

15. Binary Search

16. Star Pattern

void triangle(int n) { for (int i = 1; i <= n; i++) { for (int j = 1; j <= i; j++) System.out.print("* "); System.out.println(); } }

17. Matrix Transpose

int[][] transpose(int[][] mat) { int n = mat.length; int[][] result = new int[n][n]; for (int i = 0; i < n; i++) for (int j = 0; j < n; j++) result[j][i] = mat[i][j]; return result; }

18. Linked List Reverse

java exampleWoHoTech

Node reverse(Node head) {
    Node prev = null, curr = head;
    while (curr != null) {
        Node next = curr.next;
        curr.next = prev;
        prev = curr;
        curr = next;
    }
    return prev;
}

Important Java Programs

1. Fibonacci Series

2. Prime Number Check

3. Palindrome Check (String)

4. Reverse a Number

5. Armstrong Number

6. Factorial

7. Array Reverse

8. Find Max aur Min

9. String Reverse

10. Anagram Check

11. Duplicate Elements in Array

12. Count Characters in String

13. Two Sum

14. Bubble Sort

15. Binary Search

16. Star Pattern

17. Matrix Transpose

18. Linked List Reverse

Continue learning this concept

Important Java Programs

1. Fibonacci Series

2. Prime Number Check

3. Palindrome Check (String)

4. Reverse a Number

5. Armstrong Number

6. Factorial

7. Array Reverse

8. Find Max aur Min

9. String Reverse

10. Anagram Check

11. Duplicate Elements in Array

12. Count Characters in String

13. Two Sum

14. Bubble Sort

15. Binary Search

16. Star Pattern

17. Matrix Transpose

18. Linked List Reverse

Continue learning this concept