How to Check to See if a String Is Numeric with Java

The Java programming language contains support for a few primitive classes. Primitive classes include String for alphanumeric values, Integer for integer numbers, and Double for floating-point numbers. A String may contain any sequence of characters; in particular, some of those sequences (e.g., "-102") correspond to the decimal notation of a number. You can include code in your Java program to check if a string happens to denote a number.

Instructions

1. Check if the String denotes a valid integer by attempting to parse it as an Integer, as follows:

   Integer.parseInt(myString);

   Replace "myString" by the String variable you want to check in your code.

2. Catch the exception that the code in Step 1 will generate if the String happens to not denote a valid integer, by enclosing the code in Step 1 as follows:

   try

   {

   Integer.parseInt(myString);

   }

   catch (NumberFormatException exc)

   {

   System.out.println("Not a valid integer!");

   }

3. Check if the String denotes a valid floating-point number by attempting to parse it as an Double, as follows:

   Double.parseDouble(myString);

4. Catch the exception that the code in Step 1 will generate if the String happens to not denote a valid floating-point number, by enclosing the code in Step 3 as follows:

   try

   {

   Double.parseDouble(myString);

   }

   catch (NumberFormatException exc)

   {

   System.out.println("Not a valid floating-point number!");

   }

References

• Sun Microsystems: Integer.parseInt Method
• Sun Microsystems: Double.parseInt Method