Find First Non-Repeated Character in a String in Java (Interview Program)

In this post, we’ll write a Java program to find the first non-repeated character in a string. This is a popular question in coding interviews to test your understanding of string manipulation and hashing.

📌 Problem Statement

Given a string, find the first character that does not repeat anywhere else in the string. Return that character.

📚 Example

• Input: "programming" → Output: 'p'
• Input: "aabbcc" → Output: No unique character

✅ Java Program Using LinkedHashMap

import java.util.LinkedHashMap;
import java.util.Map;

public class FirstUniqueCharacter {
    public static void main(String[] args) {
        String input = "programming";
        Character result = findFirstNonRepeated(input);

        if(result != null)
            System.out.println("First non-repeated character is: " + result);
        else
            System.out.println("No unique character found.");
    }

    static Character findFirstNonRepeated(String str) {
        Map charCount = new LinkedHashMap<>();

        for (char c : str.toCharArray()) {
            charCount.put(c, charCount.getOrDefault(c, 0) + 1);
        }

        for (Map.Entry entry : charCount.entrySet()) {
            if (entry.getValue() == 1)
                return entry.getKey();
        }

        return null;
    }
}

✅ Output

First non-repeated character is: p

🧠 Interview Tip

This question can be optimized by using LinkedHashMap for maintaining order. Make sure you explain your choice of data structures clearly.

📌 Conclusion

We’ve learned how to find the first non-repeated character in a string using Java. This logic is commonly used in interviews and string-based challenges.

🔍 Master Java String & Frequency-Based Problems

Finding the first non-repeated character is a common Java interview and coding-round problem. Strengthen your string manipulation and HashMap-based logic by exploring these closely related problems and interview resources.

🧠 Java Coding Round Questions

Practice frequently asked string and HashMap-based problems.

🧵 Java String Pool & Interning

Understand how strings are stored and why immutability matters.

📦 Java Collections Interview Questions

Learn how HashMap and LinkedHashMap are used in real interview problems.

🔄 Palindrome String Program

Another classic string comparison problem asked in interviews.

🔁 Reverse String in Java

Strengthen your understanding of string traversal techniques.

🔢 String Contains Only Digits

Practice validation-based string processing problems.

🧮 Check Anagram Strings

Learn character frequency comparison using arrays and maps.

📈 Character Occurrence Count

Understand frequency counting as a foundation for many string problems.

🎯 Java Interview Questions (Freshers)

Common interview questions involving strings and collections.

🧪 Advanced Java Programs (Real-World)

Apply string processing logic in real-world Java scenarios.