How to check if a String is numeric in Java?

Abdul D.

—November 15, 2024

The ProblemThe Problem

I don’t know how to check if a String is numeric in Java.

The SolutionThe Solution

In Java, there are several ways to check whether a String is numeric, including the following common approaches:

• Using the Integer.parseInt() or Double.parseDouble() methods
• Using regular expressions
• Using the NumberUtils.isCreatable() method from the Apache Commons Lang library

Using Integer.parseInt() or Double.parseDouble()Using Integer.parseInt() or Double.parseDouble()

You can use Integer.parseInt() to check whether a string is numeric by attempting to parse it. If the string is not numeric, a NumberFormatException will be thrown.

public class Main {
    public static void main(String[] args) {
        String numericString = "123";
        String nonNumericString = "123a";

        System.out.println(isNumeric(numericString));  // 123 = true
        System.out.println(isNumeric(nonNumericString));  // 123a = false
    }

    public static boolean isNumeric(String str) {
        try {
            Integer.parseInt(str);
            return true;
        } catch (NumberFormatException e) {
            return false;
        }
    }
}

In this example, the isNumeric() method attempts to parse the string using Integer.parseInt(). If the parsing fails, it returns false.

Using Regular ExpressionsUsing Regular Expressions

You can use regular expressions to check whether a string is numeric. This method allows for more flexibility in defining what counts as a numeric value.

public class Main {
    public static void main(String[] args) {
        String numericString = "123.45";
        String nonNumericString = "123a";

        System.out.println(isNumeric(numericString));  // true
        System.out.println(isNumeric(nonNumericString));  // false
    }

    public static boolean isNumeric(String str) {
        return str.matches("-?\\d+(\\.\\d+)?");
    }
}

In this example, the regular expression -?\d+(\\.\d+)? checks whether the string is a valid number, optionally allowing for a negative sign and a decimal point.

Using Apache Commons Lang LibraryUsing Apache Commons Lang Library

The Apache Commons Lang library provides a utility method NumberUtils.isCreatable() that can be used to check whether a string is numeric.

To use this method, include the following dependency in your project:

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.12.0</version>
</dependency>

Then use it as follows:

import org.apache.commons.lang3.math.NumberUtils;

public class Main {
    public static void main(String[] args) {
        String numericString = "123.45";
        String nonNumericString = "123a";

        System.out.println(NumberUtils.isCreatable(numericString));  // true
        System.out.println(NumberUtils.isCreatable(nonNumericString));  // false
    }
}

The NumberUtils.isCreatable() method can handle integers, floating-point numbers, and even numbers in scientific notation.