The following character sequences are reserved for use as keywords and cannot be used as identifiers:

abstract     default      implements   private      throw
assert       do           import       protected    throws
boolean      double       in           public       transient
break        else         instanceof   return       try
byte         extends      int          short        void
case         final        interface    static       volatile
catch        finally      long         strictfp     while
char         float        module       super        yield
class        for          native       switch
const        goto         new          synchronized
continue     if           package      this

The keyword goto is reserved, even though it is not currently used. The keyword const is reserved for the Java programming language, but used in the XL programming language as a modifier in variable declarations. The keyword assert is introduced in the Java Language Specification, Third Edition, it is used here for the same purpose. The keywords in, module and yield are introduced by this specification.

The tokens true, false and null might appear to be keywords, however, they are technically literals.