Validate if string is a number - A Java Code Example

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This example shows how to validate if a String is a number.
The first example checks if it's and Integer by trying to parse the String to an int.
The second example can be used if you're not sure if the possible number value contained in the String will exceed the maximum value for an int.
Here we instead use the Long class to parse the String to the datatype long.

/**
* Main.java
*
* @author www.javadb.com
*/
public class Main {

    /**
     * Validates if input String is a number
     */
    public boolean checkIfNumber(String in) {

        try {

            Integer.parseInt(in);

        } catch (NumberFormatException ex) {
            return false;
        }

        return true;
    }
    /**
     * Starts the program
     *
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        Main main = new Main();
        System.out.println( main.checkIfNumber("123") );
        System.out.println( main.checkIfNumber("ABC") );
        System.out.println( main.checkIfNumber("123123123123123") );
    }
}

The output from this code will be:

true
false
false

To use the Long class, just replace the Integer class and call parseLong() instead:

/**
* Main.java
*
* @author www.javadb.com
*/
public class Main {

    /**
     * Validates if input String is a number
     */
    public boolean checkIfNumber(String in) {

        try {

            Long.parseLong(in);

        } catch (NumberFormatException ex) {
            return false;
        }

        return true;
    }
    /**
     * Starts the program
     *
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        Main main = new Main();
        System.out.println( main.checkIfNumber("123") );
        System.out.println( main.checkIfNumber("ABC") );
        System.out.println( main.checkIfNumber("123123123123123") );
    }
}

The output from this example will be:

true
false
true

See also: Validate if a String contains only numbers

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