Java: Find first non repeating character in a string

Last update on May 21 2025 12:49:16 (UTC/GMT +8 hours)

39. First Non-Repeating Character

Write a Java program to find the first non-repeating character in a string.

Visual Presentation:

Sample Solution:

Java Code:

// Importing necessary Java utilities.
import java.util.*;

// Define a class named Main.
public class Main {
    
    // Main method to execute the program.
    public static void main(String[] args) {
        // Declare and initialize a string variable.
        String str1 = "gibblegabbler";
        
        // Print the original string.
        System.out.println("The given string is: " + str1);
        
        // Loop through each character of the string.
        for (int i = 0; i < str1.length(); i++) {
            // Assume the character at index 'i' is unique initially.
            boolean unique = true;
            
            // Loop through the string again to compare characters.
            for (int j = 0; j < str1.length(); j++) {
                // Check if the characters at positions 'i' and 'j' are the same but not at the same index.
                if (i != j && str1.charAt(i) == str1.charAt(j)) {
                    // If found, set unique to false and break the loop.
                    unique = false;
                    break;
                }
            }
            
            // If the character at index 'i' is unique, print it and exit the loop.
            if (unique) {
                System.out.println("The first non-repeated character in the String is: " + str1.charAt(i));
                break;
            }
        }
    }
}

Sample Output:

The given string is: gibblegabbler
The first non repeated character in String is: i

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Java program to identify the first non-repeating character in a string using an efficient algorithm.
• Write a Java program to find the first non-repeating character in a string and return its index.
• Write a Java program to detect the first unique character in a string and then remove it from the string.
• Write a Java program to determine the first non-repeating character in a string after converting it to lowercase.

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