Java – How to Check if a string is a valid number?

Published on March 2, 2016 by abundantcode

Filed under Java

Last modified March 2, 2016

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Problem statement

You need to check if a input string contain a valid number or not.


Use the appropriate wrapper class for converting the string to numeric formats. For example Double to convert string to double as shown below.

public class Main {

    public static void main(String[] args) {
        String input = "25";
        try {
            double output = Double.parseDouble(input);
        catch(NumberFormatException ex)
            System.out.println("This is an invalid number");

When the input is a invalid number , the NumberFormatException is caused which needs to be handled by the developers.

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