How do I convert from a string into a number?


The first thing you have to be sure of is that your string actually contains a number! If not, then you'll generate a NumberFormatException. We can use the Integer class for converting from a string into an integer (or if we're dealing with decimal numbers, we can use the Double class).

The follow example shows how to convert from a string to an integer.

String numberOne = "123";
String numberTwo = "456";

// Convert numberOne and numberTwo to an int with Integer class
Integer myint1 = Integer.valueOf(numberOne);
Integer myint2 = Integer.valueOf(numberTwo);
// Add two numbers together
int number = myint1.intValue() + myint2.intValue();

You'll notice that when we need to use numbers as a data type (int), we need to convert from an Integer to an int. Confused? An Integer acts as a wrapper for our int data type (making conversion from String to number easy). When we want to use the data type, we call the intValue() method, which returns an int.