Naming variables

You choose each variable's name. A good name says what the value means: price, laps, firstName. Java has a few rules for names:

• Letters, digits, _ and $ are allowed, but a name can't start with a digit: level2 is fine, 2ndLevel isn't.
• No spaces and no other symbols, like !, - or ..
• Words that are part of Java itself, such as class, int or public, can't be names.
• Capitals matter: score and Score are two different names.

When a name is made of several words, Java programmers write it in camelCase: the first word in lower case, and every following word starting with a capital: firstName, numberOfLaps, isRaining.

String firstName = "Grace";
int yearOfBirth = 1906;
System.out.println(firstName + " was born in " + yearOfBirth + ".");

Grace was born in 1906.

A name that breaks the rules confuses the compiler, and its errors can look strange. String first name gives ';' expected, because Java reads first as the whole name and then doesn't know what name is doing there.