Check if a String Contains Only Digits in Java (2 Easy Ways)

In this tutorial, we’ll explore different ways to check whether a given string contains only numeric digits in Java. This is a common validation step in many applications and interview coding problems.

🧪 Problem Statement

Given a string, determine if it contains only digits from 0-9.

🔍 Example

• Input: "123456" → Output: true
• Input: "abc123" → Output: false
• Input: "" → Output: false

✅ Approach 1: Using Character Check

public class DigitCheck {
    public static void main(String[] args) {
        String input = "123456";
        System.out.println("Contains only digits: " + containsOnlyDigits(input));
    }

    static boolean containsOnlyDigits(String str) {
        if(str == null || str.isEmpty()) return false;

        for(char c : str.toCharArray()) {
            if(!Character.isDigit(c)) return false;
        }
        return true;
    }
}

✅ Approach 2: Using Regular Expression

public class DigitCheckRegex {
    public static void main(String[] args) {
        String input = "123abc";
        System.out.println("Contains only digits: " + input.matches("\\d+"));
    }
}

✅ Output

Contains only digits: true

🧠 Interview Tip

Using Character.isDigit() is a safe way to handle each character. Regex is faster to implement but might not give the best performance in tight loops or large datasets.

📌 Conclusion

We have discussed multiple ways to check if a string contains only digits in Java. Choose the method based on your requirement — character-by-character for better control, or regex for simplicity.

This problem is common in coding tests like those listed in Java Coding Round Questions.