array ,string...

Got it 👍 You listed a set of Java practice problems. I’ll give you clear explanations + example Java programs for each one.

---

1) Find the Smallest Number in an Array

public class SmallestInArray {
    public static void main(String[] args) {
        int[] arr = {12, 5, 8, 1, 45, -3, 9};
        int min = arr[0];

        for (int num : arr) {
            if (num < min) {
                min = num;
            }
        }

        System.out.println("Smallest number: " + min);
    }
}

---

2) Fibonacci Sequence

(a) Recursive

public class FibonacciRecursive {
    static int fib(int n) {
        if (n <= 1) return n;
        return fib(n-1) + fib(n-2);
    }

    public static void main(String[] args) {
        int n = 10;
        for (int i = 0; i < n; i++) {
            System.out.print(fib(i) + " ");
        }
    }
}

(b) Iterative

public class FibonacciIterative {
    public static void main(String[] args) {
        int n = 10, 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;
        }
    }
}

---

3) Remove Even Numbers from an Array

import java.util.*;

public class RemoveEven {
    public static void main(String[] args) {
        int[] arr = {12, 7, 5, 6, 9, 10};
        ArrayList<Integer> result = new ArrayList<>();

        for (int num : arr) {
            if (num % 2 != 0) {
                result.add(num);
            }
        }

        System.out.println("Array without evens: " + result);
    }
}

---

4) Find Duplicate Number in an Array

import java.util.*;

public class FindDuplicate {
    public static void main(String[] args) {
        int[] arr = {4, 3, 6, 2, 1, 6, 7, 3};
        HashSet<Integer> seen = new HashSet<>();

        System.out.print("Duplicates: ");
        for (int num : arr) {
            if (!seen.add(num)) {
                System.out.print(num + " ");
            }
        }
    }
}

---

5) Move Negative Numbers to Front of Array

import java.util.*;

public class MoveNegatives {
    public static void main(String[] args) {
        int[] arr = {3, -2, -5, 7, -1, 4};
        int j = 0;

        for (int i = 0; i < arr.length; i++) {
            if (arr[i] < 0) {
                int temp = arr[i];
                arr[i] = arr[j];
                arr[j] = temp;
                j++;
            }
        }

        System.out.println("After moving negatives: " + Arrays.toString(arr));
    }
}

---

6) Longest Palindromic Substring

public class LongestPalindrome {
    public static String longestPalindrome(String s) {
        if (s == null || s.length() < 1) return "";
        int start = 0, end = 0;

        for (int i = 0; i < s.length(); i++) {
            int len1 = expand(s, i, i);
            int len2 = expand(s, i, i+1);
            int len = Math.max(len1, len2);

            if (len > end - start) {
                start = i - (len-1)/2;
                end = i + len/2;
            }
        }
        return s.substring(start, end+1);
    }

    private static int expand(String s, int left, int right) {
        while (left >= 0 && right < s.length() && s.charAt(left) == s.charAt(right)) {
            left--;
            right++;
        }
        return right - left - 1;
    }

    public static void main(String[] args) {
        String s = "babad";
        System.out.println("Longest Palindrome: " + longestPalindrome(s));
    }
}

---

7) Remove Vowels from a String

public class RemoveVowels {
    public static void main(String[] args) {
        String str = "Hello World";
        String result = str.replaceAll("[AEIOUaeiou]", "");
        System.out.println("Without vowels: " + result);
    }
}

---

8) Validate Phone Number Format (Example: XXX-XXX-XXXX)

import java.util.regex.*;

public class PhoneValidator {
    public static void main(String[] args) {
        String phone = "123-456-7890";
        String regex = "\\d{3}-\\d{3}-\\d{4}";

        if (phone.matches(regex)) {
            System.out.println("Valid Phone Number");
        } else {
            System.out.println("Invalid Phone Number");
        }
    }
}

---

✅ Now you have Java solutions for all problems.

Do you want me to combine all into a single Menu-driven Program where you choose which problem to run?