+@node Java Parsers
+@section Java Parsers
+
+@menu
+* Java Bison Interface:: Asking for Java parser generation
+* Java Semantic Values:: %type and %token vs. Java
+* Java Location Values:: The position and location classes
+* Java Parser Interface:: Instantiating and running the parser
+* Java Scanner Interface:: Java scanners, and pure parsers
+* Java Differences:: Differences between C/C++ and Java Grammars
+@end menu
+
+@node Java Bison Interface
+@subsection Java Bison Interface
+@c - %language "Java"
+@c - initial action
+
+(The current Java interface is experimental and may evolve.
+More user feedback will help to stabilize it.)
+
+The Java parser skeletons are selected using a language directive,
+@samp{%language "Java"}, or the synonymous command-line option
+@option{--language=java}.
+
+When run, @command{bison} will create several entities whose name
+starts with @samp{YY}. Use the @samp{%name-prefix} directive to
+change the prefix, see @ref{Decl Summary}; classes can be placed
+in an arbitrary Java package using a @samp{%define package} section.
+
+The parser class defines an inner class, @code{Location}, that is used
+for location tracking. If the parser is pure, it also defines an
+inner interface, @code{Lexer}; see @ref{Java Scanner Interface} for the
+meaning of pure parsers when the Java language is chosen. Other than
+these inner class/interface, and the members described in @ref{Java
+Parser Interface}, all the other members and fields are preceded
+with a @code{yy} prefix to avoid clashes with user code.
+
+No header file can be generated for Java parsers; you must not pass
+@option{-d}/@option{--defines} to @command{bison}, nor use the
+@samp{%defines} directive.
+
+By default, the @samp{YYParser} class has package visibility. A
+declaration @samp{%define "public"} will change to public visibility.
+Remember that, according to the Java language specification, the name
+of the @file{.java} file should match the name of the class in this
+case.
+
+Similarly, a declaration @samp{%define "abstract"} will make your
+class abstract.
+
+You can create documentation for generated parsers using Javadoc.
+
+@node Java Semantic Values
+@subsection Java Semantic Values
+@c - No %union, specify type in %type/%token.
+@c - YYSTYPE
+@c - Printer and destructor
+
+There is no @code{%union} directive in Java parsers. Instead, the
+semantic values' types (class names) should be specified in the
+@code{%type} or @code{%token} directive:
+
+@example
+%type <Expression> expr assignment_expr term factor
+%type <Integer> number
+@end example
+
+By default, the semantic stack is declared to have @code{Object} members,
+which means that the class types you specify can be of any class.
+To improve the type safety of the parser, you can declare the common
+superclass of all the semantic values using the @samp{%define} directive.
+For example, after the following declaration:
+
+@example
+%define "stype" "ASTNode"
+@end example
+
+@noindent
+any @code{%type} or @code{%token} specifying a semantic type which
+is not a subclass of ASTNode, will cause a compile-time error.
+
+Types used in the directives may be qualified with a package name.
+Primitive data types are accepted for Java version 1.5 or later. Note
+that in this case the autoboxing feature of Java 1.5 will be used.
+
+Java parsers do not support @code{%destructor}, since the language
+adopts garbage collection. The parser will try to hold references
+to semantic values for as little time as needed.
+
+Java parsers do not support @code{%printer}, as @code{toString()}
+can be used to print the semantic values. This however may change
+(in a backwards-compatible way) in future versions of Bison.
+
+
+@node Java Location Values
+@subsection Java Location Values
+@c - %locations
+@c - class Position
+@c - class Location
+
+When the directive @code{%locations} is used, the Java parser
+supports location tracking, see @ref{Locations, , Locations Overview}.
+An auxiliary user-defined class defines a @dfn{position}, a single point
+in a file; Bison itself defines a class representing a @dfn{location},
+a range composed of a pair of positions (possibly spanning several
+files). The location class is an inner class of the parser; the name
+is @code{Location} by default, may also be renamed using @code{%define
+"location_type" "@var{class-name}}.
+
+The location class treats the position as a completely opaque value.
+By default, the class name is @code{Position}, but this can be changed
+with @code{%define "position_type" "@var{class-name}"}.
+
+
+@deftypemethod {Location} {Position} begin
+@deftypemethodx {Location} {Position} end
+The first, inclusive, position of the range, and the first beyond.
+@end deftypemethod
+
+@deftypemethod {Location} {void} toString ()
+Prints the range represented by the location. For this to work
+properly, the position class should override the @code{equals} and
+@code{toString} methods appropriately.
+@end deftypemethod
+
+
+@node Java Parser Interface
+@subsection Java Parser Interface
+@c - define parser_class_name
+@c - Ctor
+@c - parse, error, set_debug_level, debug_level, set_debug_stream,
+@c debug_stream.
+@c - Reporting errors
+
+The output file defines the parser class in the package optionally
+indicated in the @code{%define package} section. The class name defaults
+to @code{YYParser}. The @code{YY} prefix may be changed using
+@samp{%name-prefix}; alternatively, you can use @samp{%define
+"parser_class_name" "@var{name}"} to give a custom name to the class.
+The interface of this class is detailed below. It can be extended using
+the @code{%parse-param} directive; each occurrence of the directive will
+add a field to the parser class, and an argument to its constructor.
+
+@deftypemethod {YYParser} {} YYParser (@var{type1} @var{arg1}, ...)
+Build a new parser object. There are no arguments by default, unless
+@samp{%parse-param @{@var{type1} @var{arg1}@}} was used.
+@end deftypemethod
+
+@deftypemethod {YYParser} {boolean} parse ()
+Run the syntactic analysis, and return @code{true} on success,
+@code{false} otherwise.
+@end deftypemethod
+
+@deftypemethod {YYParser} {boolean} recovering ()
+During the syntactic analysis, return @code{true} if recovering
+from a syntax error. @xref{Error Recovery}.
+@end deftypemethod
+
+@deftypemethod {YYParser} {java.io.PrintStream} getDebugStream ()
+@deftypemethodx {YYParser} {void} setDebugStream (java.io.printStream @var{o})
+Get or set the stream used for tracing the parsing. It defaults to
+@code{System.err}.
+@end deftypemethod
+
+@deftypemethod {YYParser} {int} getDebugLevel ()
+@deftypemethodx {YYParser} {void} setDebugLevel (int @var{l})
+Get or set the tracing level. Currently its value is either 0, no trace,
+or nonzero, full tracing.
+@end deftypemethod
+
+@deftypemethod {YYParser} {void} error (Location @var{l}, String @var{m})
+The definition for this member function must be supplied by the user
+in the same way as the scanner interface (@pxref{Java Scanner
+Interface}); the parser uses it to report a parser error occurring at
+@var{l}, described by @var{m}.
+@end deftypemethod
+
+
+@node Java Scanner Interface
+@subsection Java Scanner Interface
+@c - %code lexer
+@c - %lex-param
+@c - Lexer interface
+
+Contrary to C parsers, Java parsers do not use global variables; the
+state of the parser is always local to an instance of the parser class.
+Therefore, all Java parsers are ``pure'', and the @code{%pure-parser}
+directive does not do anything when used in Java.
+@c FIXME: But a bit farther it is stated that
+@c If @code{%pure-parser} is not specified, the lexer interface
+@c resides in the same class (@code{YYParser}) as the Bison-generated
+@c parser. The fields and methods that are provided to
+@c this end are as follows.
+
+The scanner always resides in a separate class than the parser.
+Still, there are two possible ways to interface a Bison-generated Java
+parser with a scanner, that is, the scanner may reside in a separate file
+than the Bison grammar, or in the same file. The interface
+to the scanner is similar in the two cases.
+
+In the first case, where the scanner in the same file as the grammar, the
+scanner code has to be placed in @code{%code lexer} blocks. If you want
+to pass parameters from the parser constructor to the scanner constructor,
+specify them with @code{%lex-param}; they are passed before
+@code{%parse-param}s to the constructor.
+
+In the second case, the scanner has to implement the @code{Lexer} interface,
+which is defined within the parser class (e.g., @code{YYParser.Lexer}).
+The constructor of the parser object will then accept an object
+implementing the interface; @code{%lex-param} is not used in this
+case.
+
+In both cases, the scanner has to implement the following methods.
+
+@deftypemethod {Lexer} {void} yyerror (Location @var{l}, String @var{m})
+As explained in @pxref{Java Parser Interface}, this method is defined
+by the user to emit an error message. The first parameter is omitted
+if location tracking is not active. Its type can be changed using
+@samp{%define "location_type" "@var{class-name}".}
+@end deftypemethod
+
+@deftypemethod {Lexer} {int} yylex (@var{type1} @var{arg1}, ...)
+Return the next token. Its type is the return value, its semantic
+value and location are saved and returned by the ther methods in the
+interface. Invocations of @samp{%lex-param @{@var{type1}
+@var{arg1}@}} yield additional arguments.
+@end deftypemethod
+
+@deftypemethod {Lexer} {Position} getStartPos ()
+@deftypemethodx {Lexer} {Position} getEndPos ()
+Return respectively the first position of the last token that
+@code{yylex} returned, and the first position beyond it. These
+methods are not needed unless location tracking is active.
+
+The return type can be changed using @samp{%define "position_type"
+"@var{class-name}".}
+@end deftypemethod
+
+@deftypemethod {Lexer} {Object} getLVal ()
+Return the semantical value of the last token that yylex returned.
+
+The return type can be changed using @samp{%define "stype"
+"@var{class-name}".}
+@end deftypemethod
+
+
+The lexer interface resides in the same class (@code{YYParser}) as the
+Bison-generated parser.
+The fields and methods that are provided to this end are as follows.
+
+@deftypemethod {YYParser} {void} error (Location @var{l}, String @var{m})
+As already explained (@pxref{Java Parser Interface}), this method is defined
+by the user to emit an error message. The first parameter is not used
+unless location tracking is active. Its type can be changed using
+@samp{%define "location_type" "@var{class-name}".}
+@end deftypemethod
+
+@deftypemethod {YYParser} {int} yylex (@var{type1} @var{arg1}, ...)
+Return the next token. Its type is the return value, its semantic
+value and location are saved into @code{yylval}, @code{yystartpos},
+@code{yyendpos}. Invocations of @samp{%lex-param @{@var{type1}
+@var{arg1}@}} yield additional arguments.
+@end deftypemethod
+
+@deftypecv {Field} {YYParser} Position yystartpos
+@deftypecvx {Field} {YYParser} Position yyendpos
+Contain respectively the first position of the last token that yylex
+returned, and the first position beyond it. These methods are not
+needed unless location tracking is active.
+
+The field's type can be changed using @samp{%define "position_type"
+"@var{class-name}".}
+@end deftypecv
+
+@deftypecv {Field} {YYParser} Object yylval
+Return respectively the first position of the last token that yylex
+returned, and the first position beyond it.
+
+The field's type can be changed using @samp{%define "stype"
+"@var{class-name}".}
+@end deftypecv
+
+@node Java Differences
+@subsection Differences between C/C++ and Java Grammars
+
+The different structure of the Java language forces several differences
+between C/C++ grammars, and grammars designed for Java parsers. This
+section summarizes these differences.
+
+@itemize
+@item
+Java lacks a preprocessor, so the @code{YYERROR}, @code{YYACCEPT},
+@code{YYABORT} symbols (@pxref{Table of Symbols}) cannot obviously be
+macros. Instead, they should be preceded by @code{return} when they
+appear in an action. The actual definition of these symbols is
+opaque to the Bison grammar, and it might change in the future. The
+only meaningful operation that you can do, is to return them.
+
+Note that of these three symbols, only @code{YYACCEPT} and
+@code{YYABORT} will cause a return from the @code{yyparse}
+method@footnote{Java parsers include the actions in a separate
+method than @code{yyparse} in order to have an intuitive syntax that
+corresponds to these C macros.}.
+
+@item
+The prolog declarations have a different meaning than in C/C++ code.
+@table @asis
+@item @code{%code imports}
+blocks are placed at the beginning of the Java source code. They may
+include copyright notices. For a @code{package} declarations, it is
+suggested to use @code{%define package} instead.
+
+@item unqualified @code{%code}
+blocks are placed inside the parser class.
+
+@item @code{%code lexer}
+blocks, if specified, should include the implementation of the
+scanner. If there is no such block, the scanner can be any class
+that implements the appropriate interface (see @pxref{Java Scanner
+Interface}).
+@end table
+
+Other @code{%code} blocks are not supported in Java parsers.
+The epilogue has the same meaning as in C/C++ code and it can
+be used to define other classes used by the parser.
+@end itemize
+
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