Top Java Coding Round Questions Asked in Interviews (With Detailed Solutions)
Java coding rounds are a crucial part of placement drives and technical interviews conducted by companies such as TCS, Infosys, Capgemini, Wipro, Cognizant, and many others. To help you prepare effectively, here is a well-structured collection of commonly asked Java programming questions along with clear, beginner-friendly solutions.
Each problem includes:
- A sample input/output
- Java code solution
- Explanation
- Time & space complexity
- Interview tip (What interviewers expect)
🧠 1. Reverse Each Word in a Sentence
Asked In: Infosys, Wipro
Input: "Java is awesome"
Output: "avaJ si emosewa"
public class ReverseWords {
public static void main(String[] args) {
String input = "Java is awesome";
String[] words = input.split(" ");
StringBuilder result = new StringBuilder();
for (String word : words) {
result.append(new StringBuilder(word).reverse())
.append(" ");
}
System.out.println(result.toString().trim());
}
}
Explanation
The sentence is split into individual words. Each word is reversed using StringBuilder.reverse() and appended back.
Time Complexity: O(n)
Space Complexity: O(n)
StringBuilder is efficient for string manipulation.🔢 2. Count Letters, Digits & Special Characters
Asked In: Capgemini
Input: "Java123@#!"
Output:
Letters = 4
Digits = 3
Specials = 3
public class CountTypes {
public static void main(String[] args) {
String str = "Java123@#!";
int letters = 0, digits = 0, specials = 0;
for (char ch : str.toCharArray()) {
if (Character.isLetter(ch)) letters++;
else if (Character.isDigit(ch)) digits++;
else specials++;
}
System.out.println("Letters=" + letters + ", Digits=" + digits + ", Specials=" + specials);
}
}
Explanation
The program iterates through each character and checks its type using Java's inbuilt Character class.
Time Complexity: O(n)
🔁 3. Print Fibonacci Series up to N Terms
Asked In: Wipro, Cognizant
Input: 6
Output: 0 1 1 2 3 5
public class FibonacciSeries {
public static void main(String[] args) {
int n = 6, 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;
}
}
}
Explanation
The Fibonacci sequence begins with 0 and 1. Each new number is the sum of the previous two.
Time Complexity: O(n)
🎯 4. Find the Second Highest Number in an Array
Asked In: TCS, Infosys
Input: [2, 10, 5, 7]
Output: 7
public class SecondLargest {
public static void main(String[] args) {
int[] arr = {2, 10, 5, 7};
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 largest: " + second);
}
}
Explanation
The solution keeps track of both the highest and second-highest numbers in a single scan.
Time Complexity: O(n)
Space Complexity: O(1)
✅ 5. Check if a String is Palindrome
Asked In: Cognizant, Capgemini
Input: "madam"
Output: true
public class PalindromeCheck {
public static void main(String[] args) {
String str = "madam";
String reversed = new StringBuilder(str).reverse().toString();
System.out.println(str.equals(reversed));
}
}
Explanation
A string is a palindrome if it reads the same forward and backward.
Time Complexity: O(n)
reverse() — be prepared.🧩 6. Print Right-Angled Triangle Star Pattern
Asked In: TCS NQT
Input: 5
Output:
*
**
***
****
*****
public class TrianglePattern {
public static void main(String[] args) {
for (int i = 1; i <= 5; i++) {
System.out.println("*".repeat(i));
}
}
}
Explanation
Star patterns are frequently asked to test looping logic and nested loops.
💡 7. Count the Frequency of Each Character
Asked In: Infosys, Wipro
Input: "apple"
Output:
a = 1
p = 2
l = 1
e = 1
import java.util.*;
public class CharFrequency {
public static void main(String[] args) {
String str = "apple";
Map<Character, Integer> map = new LinkedHashMap<>();
for (char c : str.toCharArray()) {
map.put(c, map.getOrDefault(c, 0) + 1);
}
map.forEach((k, v) -> System.out.println(k + " = " + v));
}
}
Explanation
The LinkedHashMap preserves insertion order while counting the frequency of each character.
Time Complexity: O(n)
📌 Conclusion
These Java coding interview questions are widely asked across service-based and product-based companies. Practice writing optimized and clean code, and always be ready to explain your logic clearly. This is often more important to interviewers than the final answer itself.
Next article: Advanced Java Coding Round Problems Asked in Product Companies
❓ Frequently Asked Questions (FAQ)
Strings, arrays, loops, collections, recursion, pattern printing, and basic math logic.
These cover 80% of commonly asked beginner-level coding problems.
No — understand logic. Interviewers test your thought process, not memorization.