String in Java 20

In Java, you can check if a string is a number by using the NumberUtils class from the Apache Commons Lang library or by using the NumberFormatException class. Here are examples of both methods:

Using NumberUtils class:

import org.apache.commons.lang3.math.NumberUtils;
public class CheckNumberString {

    public static void main(String[] args) {

        String numStr = "123.45";

        boolean isNum = NumberUtils.isCreatable(numStr);

        System.out.println(isNum);

    }

}

Output: true, because 123.45 is a number.

Using NumberFormatException class:

public class CheckNumberString {
    public static void main(String[] args) {
        String numStr = "abc123";
        try {
            Double.parseDouble(numStr);
            System.out.println("This string is a number.");
        } catch (NumberFormatException e) {
            System.out.println("This string is not a number.");
        }
    }
}

Output: This string is not a number., because abc123 is not a number.

Note that in the second example, we are trying to convert the string to a Double and catching the NumberFormatException if it occurs, indicating that the string is not a number.