Main design goals of JFlex

•  Full unicode support
•  Fast generated scanners
•  Fast scanner generation
•  More convenient specification syntax
•  Better platform independence
•  JLex compatibility

List of JFlex features

• All features of JLex, and additionally:
• Faster generated scanners
• Faster Scanner generation (independent of the input character set)
• Three different kinds of generated code for best performance/size.
• Predefined character classes

• Comments in all parts of the specification
• Macro definitions are regular expressions, not just text
• Cycles in macro definitions are detected and reported at generation time
• Platform independent end of line operator "$"
• Beginning of line operator "^" works as expected (not consuming newlines)
• Grouping of rules with same lexical states
• Comments, character literals and strings in actions are handled correctly

• Builtin support for the CUP parser generator
• Column counting
• Standalone scanners (as with C/C++ flex)
• Debugging support

New since version 1.1

• whitespace characters " " (space) and "\t" (tab) in regular expressions
• flex style repeat expressions r{n} and r{n,m}
• switch for case insensitive scanners
• switch for closing the input stream automatically at the end of file
• a method for closing the input stream
• a method for getting the current lexical state
• a method for rereading matched text
• backup of files that are overwitten in the generation process

New since version 1.2

• command line switches for more customization
• external scanner skeleton files
• <<EOF>> rules as in lex and flex.
• | action as in flex
• arbitrary trailing context with the / operator
• %extends option for subclassing
• %final and %abstract class modifiers
• more conventient declaration of exceptions

New since version 1.3

• empty charclass []
• any (=negated empty) charclass [^]
• negation operator ! for regexps
• upto operator ~ for regexps
• customizable buffer size with %buffer
• char yycharat(int) for efficient access to single characters in matched text
• split up of too large lex tables for even larger scanner sizes
• external skeleton with support for nested input streams
• customize for internal error handling in yy_ScanError
• new resetStream method for reusing scanner objects
• BYacc/J support (%byaccj)
• include files in lexer specs with %include

New since version 1.4

• new, very fast minimization algorithm
• new --jlex option for strict compatibility to JLex
• support for even larger scanners (up to 64K DFA states)
• faster character classes
• new %apiprivate switch that causes all generated and skeleton methods to be made private
• allow user defined javadoc class comments
• optional parameter to %eofclose: "%eofclose false" turns off %eofclose if it was turned on previously (e.g. by %cup)
• some internal changes: jflex build script switched to ant, better integration with build tools and IDEs, change scheme for generated names to comply with Java naming standard
• since 1.4.2: general efficient lookahead algorithm