Java defines a list of words called keywords.
Keywords in Java can only be used in the contexts defined by the Java language.
Keywords in Java cannot be used as identifiers.
List of Keywords and Reserved Words in Java
abstract continue for new switch assert default goto package synchronized boolean do if private this break double implements protected throw byte else import public throws case enum instanceof return transient catch extends int short try char final interface static void class finally long strictfp volatile const float native super while
The two keywords, const and goto, are not currently used in Java.
They are reserved keywords and they cannot be used as identifiers.
In addition to all the keywords, three words, true, false, and null, cannot be used as identifiers.
true and false are boolean literals and null is a reference literal.