# Java: Converting Strings to Numbers

To convert a string value to a number (for example, to convert the String value in a text field to an int), use these methods. Assume the following declarations:

    String s; int i;  long l;  float f;  double d;

type | Example statement
`int` | `i = Integer.parseInt(s);`
`long` | `l = Long.parseLong(s);`
`float` | `f = Float.parseFloat(s);`
`double` | `d = Double.parseDouble(s);`

If s is null or not a valid representation of a number of that type, these methods will throw (generate) a `NumberFormatException`. See below.

## Handling NumberFormatExceptions

Put number conversions inside a `try . . . catch` statement so that you can do something if bad input is entered. The conversion method will throw a NumberFormatException when there is bad input. Catch the NumberFormatException, and do something to handle this error condition. Put your conversion in the `try` clause, and the error handling in the `catch` clause. Here is an example of the kind of utility function you might write to do this checking.

    //--- Utility function to get int using a dialog.
    public static int getInt(String mess) {
        int val;
        while (true) { // loop until we get a valid int
            String s = JOptionPane.showInputDialog(null, mess);
            try {
                val = Integer.parseInt(s);
                break;  // exit loop with valid int >>>>>>>>>>>>>>>>>>>>>>
            }catch (NumberFormatException nx) {
                JOptionPane.showMessageDialog(null, "Enter valid integer");
            }
        }
        return val;
    }//end getInt

## Non-decimal Integers

Convert integers with some base (radix) other than 10 by using these two methods. Typically these will be hexadecimal (base 16) or binary (base 2) numbers.

type | Example statement
`int` | `i = Integer.parseInt(s, radix);`
`long` | `l = Long.parseLong(s, radix);`

For example, to convert a string containing the hexadecimal number "F7" to an integer, call

    i = Integer.parseInt("F7", 16)

## See also

- Exceptions
- Example - Simple Calculator.