A keyword is a word whose meaning is defined by the programming language. Java keywords and reserved Words:
abstract class extends implements null strictfp true assert const false import package super try boolean continue final instanceof private switch void break default finally int protected synchronized volatile byte do float interface public this while case double for long return throw catch else goto native short throws char enum if new static transient
An identifier is a word used by a programmer to name a variable, method, class, or label. Keywords and reserved words may not be used as identifiers. An identifier must begin with a letter, a dollar sign ($), or an underscore (_); subsequent characters may be letters, dollar signs, underscores, or digits.
Some examples are:
foobar // legal Myclass // legal $a // legal 3_a // illegal: starts with a digit !theValue // illegal: bad 1st char
Java Identifiers are case sensitive.
For example, myValue and MyValue are distinct identifiers.
Identifiers are used for class names, method names, and variable names. An identifier may be any sequence of uppercase and lowercase letters, numbers, or the underscore and dollar-sign characters. Identifiers must not begin with a number. Java Identifiers are case-sensitive. The following code illustrates some examples of valid identifiers:
public class Main { public static void main(String[] argv) { int ATEST, count, i1, $Atest, this_is_a_test; } }
The following code shows invalid variable names include:
public class Main { public static void main(String[] argv){ int 2count, h-l, a/b, } }
If you try to compile this code, you will get the following error message: