Top Java Code-Based Interview Questions for Experienced Developers with 5 years of experience

Java Code-Based Interview Questions with Answers

Top Java Code-Based Interview Questions for Experienced Developers with 5 years of experience. 

1. Detect Duplicates in an Array

Question: Write a Java program to detect duplicates in an array and print the duplicates.

import java.util.HashSet;

public class DuplicateDetector {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3, 4, 5, 2, 4, 6};
        HashSet<Integer> set = new HashSet<>();
        System.out.println("Duplicate elements:");
        for (int num : numbers) {
            if (!set.add(num)) {
                System.out.println(num);
            }
        }
    }
}

Output:

Duplicate elements:
2
4

Explanation: The HashSet does not allow duplicate values. Each element is checked if it can be added to the set; if not, it means it’s a duplicate and is printed.

2. String Reverse Without Using Built-In Functions

Question: Write a Java method to reverse a string without using any built-in functions.

public class StringReverse {
    public static void main(String[] args) {
        String str = "Java";
        System.out.println("Reversed: " + reverseString(str));
    }

    public static String reverseString(String s) {
        char[] chars = s.toCharArray();
        int left = 0, right = chars.length - 1;
        while (left < right) {
            char temp = chars[left];
            chars[left] = chars[right];
            chars[right] = temp;
            left++;
            right--;
        }
        return new String(chars);
    }
}

Output:

Reversed: avaJ

Explanation: This solution uses a two-pointer approach to swap characters from both ends of the string until they meet in the middle.

3. Find the Second Largest Element in an Array

Question: Write a Java program to find the second largest element in an array.

public class SecondLargestFinder {
    public static void main(String[] args) {
        int[] arr = {10, 20, 4, 45, 99};
        System.out.println("Second largest element is: " + findSecondLargest(arr));
    }

    public static int findSecondLargest(int[] array) {
        int largest = Integer.MIN_VALUE, secondLargest = Integer.MIN_VALUE;
        for (int num : array) {
            if (num > largest) {
                secondLargest = largest;
                largest = num;
            } else if (num > secondLargest && num != largest) {
                secondLargest = num;
            }
        }
        return secondLargest;
    }
}

Output:

Second largest element is: 45

Explanation: This code iterates through the array, updating the largest and second largest numbers based on conditions, ensuring secondLargest has the second-highest value at the end.

4. FizzBuzz Program

Question: Write a program that prints numbers from 1 to 15. For multiples of 3, print "Fizz" instead of the number, and for multiples of 5, print "Buzz." For numbers that are multiples of both 3 and 5, print "FizzBuzz."

public class FizzBuzz {
    public static void main(String[] args) {
        for (int i = 1; i <= 15; i++) {
            if (i % 3 == 0 && i % 5 == 0) {
                System.out.println("FizzBuzz");
            } else if (i % 3 == 0) {
                System.out.println("Fizz");
            } else if (i % 5 == 0) {
                System.out.println("Buzz");
            } else {
                System.out.println(i);
            }
        }
    }
}

Output:

1
2
Fizz
4
Buzz
Fizz
7
8
Fizz
Buzz
11
Fizz
13
14
FizzBuzz

Explanation: This program checks each number to see if it’s divisible by 3, 5, or both, and prints the appropriate response.

5. Count Occurrences of Each Character in a String

Question: Write a Java program to count the occurrences of each character in a given string.

import java.util.HashMap;

public class CharacterCounter {
    public static void main(String[] args) {
        String str = "programming";
        countCharacters(str);
    }

    public static void countCharacters(String str) {
        HashMap<Character, Integer> map = new HashMap<>();
        for (char ch : str.toCharArray()) {
            map.put(ch, map.getOrDefault(ch, 0) + 1);
        }
        System.out.println(map);
    }
}

Output:

{p=1, r=2, o=1, g=2, a=1, m=2, i=1, n=1}

Explanation: The program uses a HashMap to store each character as a key and its occurrence count as the value. The getOrDefault method provides a default value of 0 if the character is not already in the map.

These questions cover basic to intermediate Java concepts, such as collections, loops, and string manipulation, which are helpful for a Java developer with 5 years of experience.