In the Java programming language, a Keyword is any one of 51 reserved words that have a predefined meaning in the language; because of this, programmers cannot use keywords as names for variables, methods, classes, or as any other identifier. Of these 51 keywords, 49 are in use and 2 are not in use. Due to their special functions in the language, most integrated development environments for Java use syntax highlighting to display keywords in a different colour for easy identification.