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💻 Java Interview Questions and Answers (Part 4 – Practical Coding & Programs)

Coding questions are the heart of any Java interview.
Even if you understand all the theory, you must know how to write small working programs that show your problem-solving skills.

Let’s go through 30+ most asked Java coding questions with easy explanations and outputs 👇

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🔹 1. Write a program to print “Hello World” in Java.

Answer:

class Hello {
    public static void main(String[] args) {
        System.out.println("Hello World");
    }
}

✅ Output: Hello World

👉 This is the simplest Java program that every beginner starts with.

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🔹 2. Write a program to find the sum of two numbers.

class Sum {
    public static void main(String[] args) {
        int a = 10, b = 20;
        int sum = a + b;
        System.out.println("Sum: " + sum);
    }
}

✅ Output: Sum: 30

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🔹 3. Write a program to check if a number is even or odd.

class EvenOdd {
    public static void main(String[] args) {
        int num = 5;
        if(num % 2 == 0)
            System.out.println("Even");
        else
            System.out.println("Odd");
    }
}

✅ Output: Odd

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🔹 4. Program to find the largest of three numbers.

class Largest {
    public static void main(String[] args) {
        int a = 10, b = 25, c = 15;
        if(a >= b && a >= c)
            System.out.println(a + " is largest");
        else if(b >= a && b >= c)
            System.out.println(b + " is largest");
        else
            System.out.println(c + " is largest");
    }
}

✅ Output: 25 is largest

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🔹 5. Program to check if a number is prime.

class Prime {
    public static void main(String[] args) {
        int num = 7;
        boolean flag = true;
        for(int i = 2; i <= num/2; i++) {
            if(num % i == 0) {
                flag = false;
                break;
            }
        }
        if(flag)
            System.out.println(num + " is prime");
        else
            System.out.println(num + " is not prime");
    }
}

✅ Output: 7 is prime

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🔹 6. Program to reverse a number.

class ReverseNumber {
    public static void main(String[] args) {
        int num = 1234, rev = 0;
        while(num != 0) {
            rev = rev * 10 + num % 10;
            num = num / 10;
        }
        System.out.println("Reversed: " + rev);
    }
}

✅ Output: Reversed: 4321

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🔹 7. Program to check if a number is palindrome.

class Palindrome {
    public static void main(String[] args) {
        int num = 121, original = num, rev = 0;
        while(num != 0) {
            rev = rev * 10 + num % 10;
            num = num / 10;
        }
        if(original == rev)
            System.out.println("Palindrome");
        else
            System.out.println("Not Palindrome");
    }
}

✅ Output: Palindrome

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🔹 8. Program to find factorial of a number.

class Factorial {
    public static void main(String[] args) {
        int num = 5;
        int fact = 1;
        for(int i = 1; i <= num; i++) {
            fact *= i;
        }
        System.out.println("Factorial: " + fact);
    }
}

✅ Output: Factorial: 120

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🔹 9. Program to find Fibonacci series up to n terms.

class Fibonacci {
    public static void main(String[] args) {
        int n = 7, 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;
        }
    }
}

✅ Output: 0 1 1 2 3 5 8

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🔹 10. Program to find sum of digits of a number.

class SumOfDigits {
    public static void main(String[] args) {
        int num = 123, sum = 0;
        while(num > 0) {
            sum += num % 10;
            num /= 10;
        }
        System.out.println("Sum of digits: " + sum);
    }
}

✅ Output: Sum of digits: 6

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🔹 11. Program to swap two numbers without using third variable.

class Swap {
    public static void main(String[] args) {
        int a = 10, b = 20;
        a = a + b;
        b = a - b;
        a = a - b;
        System.out.println("a: " + a + ", b: " + b);
    }
}

✅ Output: a: 20, b: 10

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🔹 12. Program to check if a string is palindrome.

class StringPalindrome {
    public static void main(String[] args) {
        String str = "madam";
        String rev = new StringBuilder(str).reverse().toString();
        if(str.equals(rev))
            System.out.println("Palindrome String");
        else
            System.out.println("Not Palindrome");
    }
}

✅ Output: Palindrome String

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🔹 13. Program to count vowels and consonants in a string.

class CountVowels {
    public static void main(String[] args) {
        String str = "Hello Java";
        int vowels = 0, consonants = 0;
        str = str.toLowerCase();
        for(char c : str.toCharArray()) {
            if("aeiou".indexOf(c) != -1)
                vowels++;
            else if(Character.isLetter(c))
                consonants++;
        }
        System.out.println("Vowels: " + vowels);
        System.out.println("Consonants: " + consonants);
    }
}

✅ Output:
Vowels: 4
Consonants: 4

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🔹 14. Program to reverse a string.

class ReverseString {
    public static void main(String[] args) {
        String str = "Java";
        String rev = "";
        for(int i = str.length() - 1; i >= 0; i--) {
            rev += str.charAt(i);
        }
        System.out.println("Reversed: " + rev);
    }
}

✅ Output: Reversed: avaJ

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🔹 15. Program to find largest element in an array.

class LargestArray {
    public static void main(String[] args) {
        int arr[] = {10, 25, 3, 50, 2};
        int max = arr[0];
        for(int n : arr) {
            if(n > max)
                max = n;
        }
        System.out.println("Largest: " + max);
    }
}

✅ Output: Largest: 50

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🔹 16. Program to sort an array in ascending order.

import java.util.Arrays;
class SortArray {
    public static void main(String[] args) {
        int arr[] = {5, 1, 4, 2, 3};
        Arrays.sort(arr);
        System.out.println(Arrays.toString(arr));
    }
}

✅ Output: [1, 2, 3, 4, 5]

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🔹 17. Program to find second largest element in an array.

import java.util.Arrays;
class SecondLargest {
    public static void main(String[] args) {
        int arr[] = {12, 35, 1, 10, 34, 1};
        Arrays.sort(arr);
        System.out.println("Second Largest: " + arr[arr.length - 2]);
    }
}

✅ Output: Second Largest: 34

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🔹 18. Program to check Armstrong number.

class Armstrong {
    public static void main(String[] args) {
        int num = 153, temp = num, sum = 0;
        while(num != 0) {
            int digit = num % 10;
            sum += digit * digit * digit;
            num /= 10;
        }
        if(sum == temp)
            System.out.println("Armstrong Number");
        else
            System.out.println("Not Armstrong");
    }
}

✅ Output: Armstrong Number

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🔹 19. Program to find duplicate elements in an array.

class Duplicate {
    public static void main(String[] args) {
        int arr[] = {1, 2, 3, 2, 4, 1};
        for(int i = 0; i < arr.length; i++) {
            for(int j = i + 1; j < arr.length; j++) {
                if(arr[i] == arr[j])
                    System.out.println("Duplicate: " + arr[j]);
            }
        }
    }
}

✅ Output:
Duplicate: 2
Duplicate: 1

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🔹 20. Program to count words in a string.

class CountWords {
    public static void main(String[] args) {
        String str = "Java is fun to learn";
        String[] words = str.split(" ");
        System.out.println("Word Count: " + words.length);
    }
}

✅ Output: Word Count: 5

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🔹 21. Program to find factorial using recursion.

class FactorialRec {
    static int fact(int n) {
        if(n == 1)
            return 1;
        else
            return n * fact(n - 1);
    }
    public static void main(String[] args) {
        System.out.println("Factorial: " + fact(5));
    }
}

✅ Output: Factorial: 120

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🔹 22. Program to check leap year.

class LeapYear {
    public static void main(String[] args) {
        int year = 2024;
        if((year % 4 == 0 && year % 100 != 0) || year % 400 == 0)
            System.out.println("Leap Year");
        else
            System.out.println("Not Leap Year");
    }
}

✅ Output: Leap Year

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🔹 23. Program to count number of digits in a number.

class CountDigits {
    public static void main(String[] args) {
        int num = 12345, count = 0;
        while(num != 0) {
            num = num / 10;
            count++;
        }
        System.out.println("Digits: " + count);
    }
}

✅ Output: Digits: 5

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🔹 24. Program to find smallest element in an array.

class Smallest {
    public static void main(String[] args) {
        int arr[] = {10, 2, 8, 3};
        int min = arr[0];
        for(int n : arr) {
            if(n < min)
                min = n;
        }
        System.out.println("Smallest: " + min);
    }
}

✅ Output: Smallest: 2

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🔹 25. Program to print multiplication table.

class Table {
    public static void main(String[] args) {
        int num = 5;
        for(int i = 1; i <= 10; i++)
            System.out.println(num + " x " + i + " = " + (num * i));
    }
}

✅ Output:
5 x 1 = 5
5 x 2 = 10
…
5 x 10 = 50

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🔹 26. Program to check if a character is vowel or consonant.

class VowelCheck {
    public static void main(String[] args) {
        char c = 'e';
        if("aeiouAEIOU".indexOf(c) != -1)
            System.out.println("Vowel");
        else
            System.out.println("Consonant");
    }
}

✅ Output: Vowel

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🔹 27. Program to convert string to character array.

class ToCharArray {
    public static void main(String[] args) {
        String str = "Java";
        char[] arr = str.toCharArray();
        for(char c : arr)
            System.out.print(c + " ");
    }
}

✅ Output: J a v a

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🔹 28. Program to find sum of elements in an array.

class SumArray {
    public static void main(String[] args) {
        int arr[] = {1, 2, 3, 4, 5};
        int sum = 0;
        for(int n : arr)
            sum += n;
        System.out.println("Sum: " + sum);
    }
}

✅ Output: Sum: 15

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🔹 29. Program to check if a number is perfect.

class PerfectNumber {
    public static void main(String[] args) {
        int num = 28, sum = 0;
        for(int i = 1; i < num; i++) {
            if(num % i == 0)
                sum += i;
        }
        if(sum == num)
            System.out.println("Perfect Number");
        else
            System.out.println("Not Perfect");
    }
}

✅ Output: Perfect Number

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🔹 30. Program to find power of a number.

class Power {
    public static void main(String[] args) {
        int base = 2, exp = 3, result = 1;
        for(int i = 1; i <= exp; i++) {
            result *= base;
        }
        System.out.println("Power: " + result);
    }
}

✅ Output: Power: 8

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🟢 Final Tips for Coding Rounds

• Always write clean and readable code.
• Try to explain your logic step-by-step to the interviewer.
• Use for and while loops confidently.
• Learn small string and array tricks — they appear often!
• Practice on platforms like LeetCode, HackerRank, or CodeStudio.

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