The README File for JJTreeExamples
JJTreeExamples This directory contains some simple JJTree input files intended to illustrate some of the basic ideas. All of them are based on an grammar to recognize arithmetic expressions built out of identifiers and constants. eg1.jjt This example is just the JavaCC grammar, with a little extra code in the parser's main method to call the dump method on the generated tree. It illustrates how the default behavior of JJTree will produce a tree of non-terminals. eg2.jjt This example is the same grammar as eg1.jjt with modifications to customize the generated tree. It illustrates how unnecessary intermediate nodes can be suppressed, and how actions in the grammar can attach extra information to the nodes. eg3.jjt This example is a modification of eg2.jjt with the NODE_DEFAULT_VOID option set. This instructs JJTree to treat all undecorated non-terminals as if they were decorated as #void. The default JJTree behavior is to treat such non-terminals as if they were decorated with the name of the non-terminal. eg4.jjt This is a modification of eg3.jjt with the VISITOR option set. This instructs JJTree to insert a jjtAccept() method into all nodes it generates, and to produce a visitor class. The visitor is used to dump the tree. Here are some instructions on how to run the examples and the output you can expect to see. eg1.jjt ------- The only bit of JJTree-specific code is an action in the start production that dumps the constructed parse tree when the parse is complete. It uses JJTree simple mode. The input file is eg1.jjt. trane% jjtree eg1.jjtJava Compiler Compiler Version 2.0 (Tree Builder) Copyright (c) 1996-1999 Sun Microsystems, Inc. Copyright (c) 1997-1999 Metamata, Inc. (type "jjtree" with no arguments for help) Reading from file eg1.jjt . . .File "Node.java" does not exist. Will create one. File "SimpleNode.java" does not exist. Will create one. Annotated grammar generated successfully in eg1.jj trane% JJTree has now generated the JavaCC parser source, as well as Java source for the parse tree node building classes. Running JavaCC in the normal way generates the remaining Java code. trane% javacc eg1.jj Java Compiler Compiler Version 2.0 (Parser Generator) Copyright (c) 1996-1999 Sun Microsystems, Inc. Copyright (c) 1997-1999 Metamata, Inc. (type "javacc" with no arguments for help) Reading from file eg1.jj . . . File "TokenMgrError.java" does not exist. Will create one. File "ParseException.java" does not exist. Will create one. File "Token.java" does not exist. Will create one. File "ASCII_CharStream.java" does not exist. Will create one. Parser generated successfully. trane% Compile and run the Java as usual. The expression is read from the standard input (you type in "(a + b) * (c + 1);"): trane% javac eg1.java trane% java eg1 Reading from standard input... (a + b) * (c + 1); Start Expression AdditiveExpression MultiplicativeExpression UnaryExpression Expression AdditiveExpression MultiplicativeExpression UnaryExpression Identifier MultiplicativeExpression UnaryExpression Identifier UnaryExpression Expression AdditiveExpression MultiplicativeExpression UnaryExpression Identifier MultiplicativeExpression UnaryExpression Integer Thank you. trane% eg2.jjt ------- This is a modification of the first example to illustrate how the parse tree can be customized: trane% jjtree eg2.jjt Java Compiler Compiler Version 2.0 (Tree Builder) Copyright (c) 1996-1999 Sun Microsystems, Inc. Copyright (c) 1997-1999 Metamata, Inc. (type "jjtree" with no arguments for help) Reading from file eg2.jjt . . . File "Node.java" does not exist. Will create one. File "SimpleNode.java" does not exist. Will create one. File "ASTStart.java" does not exist. Will create one. File "ASTAdd.java" does not exist. Will create one. File "ASTMult.java" does not exist. Will create one. File "ASTInteger.java" does not exist. Will create one. Annotated grammar generated successfully in eg2.jj trane% trane% javacc eg2.jj Java Compiler Compiler Version 2.0 (Parser Generator) Copyright (c) 1996-1999 Sun Microsystems, Inc. Copyright (c) 1997-1999 Metamata, Inc. (type "javacc" with no arguments for help) Reading from file eg2.jj . . . File "TokenMgrError.java" does not exist. Will create one. File "ParseException.java" does not exist. Will create one. File "Token.java" does not exist. Will create one. File "ASCII_CharStream.java" does not exist. Will create one. Parser generated successfully. trane% trane% javac eg2.java trane% java eg2 Reading from standard input... (a + b) * (c + 1); Start Mult Add Identifier: a Identifier: b Add Identifier: c Integer Thank you. trane% Look at eg2.jjt to see how node annotations can be used to restructure the parse tree, and at ASTMyID.java to see how you can write your own node classes that maintain more information from the input stream. eg3.jjt ------- This example can be run in the same manner as you ran eg2.jjt. eg4.jjt ------- This example again can be run in the same manner as you ran eg2.jjt. One thing to take care in this case is that you must run jjtree on a clean directory (that does not contain previously generated files). For example, the file SimpleNode.java is different when the option VISITOR is set to true.