Identifiers in Java

Identifiers are the names of variables, methods, classes, packages and interfaces. Unlike literals they are not the things themselves, just ways of referring to them.
In the HelloWorld program, HelloWorld, String, args, main and println are identifiers.

In Java, there are several points to remember about identifiers. They are as follows:

1. All identifiers should begin with a letter (A to Z or a to z), currency character ($) or an underscore (_).
2. After the first character identifiers can have any combination of characters.
3. A key word cannot be used as an identifier.
4. Most importantly identifiers are case sensitive.
5. Examples of legal identifiers: age, $salary, _value, __1_value
6. Examples of illegal identifiers: 123abc, -salary