JJTree Examples
A collection of simple JJTree input files intended to illustrate some of the basic ideas. All of them are based on a 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. 

Running the examples 
Here are some instructions on how to run the examples using the Ant build scripts, 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. 

,p> The input file is eg1.jjt. 


$ ant eg1
Buildfile: build.xml

eg1:
    [mkdir] Created dir: /home/tom/javacc/javacc/examples/JJTreeExamples/eg1
     [copy] Copying 1 file to /home/tom/javacc/javacc/examples/JJTreeExamples/eg1
   [jjtree] Java Compiler Compiler Version 3.2 (Tree Builder)
   [jjtree] (type "jjtree" with no arguments for help)
   [jjtree] Reading from file /home/tom/javacc/javacc/examples/JJTreeExamples/eg1.jjt . . .
   [jjtree] File "/home/tom/javacc/javacc/examples/JJTreeExamples/eg1/Node.java" does not exist.  Will create one.
   [jjtree] File "/home/tom/javacc/javacc/examples/JJTreeExamples/eg1/SimpleNode.java" does not exist.  Will create one.
   [jjtree] Annotated grammar generated successfully in /home/tom/javacc/javacc/examples/JJTreeExamples/eg1/eg1.jj
   [javacc] Java Compiler Compiler Version 3.2 (Parser Generator)
   [javacc] (type "javacc" with no arguments for help)
   [javacc] Reading from file /home/tom/javacc/javacc/examples/JJTreeExamples/eg1/eg1.jj . . .
   [javacc] File "TokenMgrError.java" does not exist.  Will create one.
   [javacc] File "ParseException.java" does not exist.  Will create one.
   [javacc] File "Token.java" does not exist.  Will create one.
   [javacc] File "SimpleCharStream.java" does not exist.  Will create one.
   [javacc] Parser generated successfully.
    [javac] Compiling 11 source files to /home/tom/javacc/javacc/examples/JJTreeExamples/eg1
     [echo] *******
     [echo] ******* Now cd into the eg1 directory and run 'java eg1' ******
     [echo] *******

BUILD SUCCESSFUL
Total time: 3 seconds
[tom@hal JJTreeExamples]$ cd eg1
[tom@hal eg1]$ 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.

eg2.jjt

This is a modification of the first example to illustrate how the parse tree can be customized: 


$ ant eg2
Buildfile: build.xml

eg2:
    [mkdir] Created dir: /home/tom/javacc/javacc/examples/JJTreeExamples/eg2
     [copy] Copying 1 file to /home/tom/javacc/javacc/examples/JJTreeExamples/eg2
     [copy] Copying 1 file to /home/tom/javacc/javacc/examples/JJTreeExamples/eg2
   [jjtree] Java Compiler Compiler Version 3.2 (Tree Builder)
   [jjtree] (type "jjtree" with no arguments for help)
   [jjtree] Reading from file /home/tom/javacc/javacc/examples/JJTreeExamples/eg2.jjt . . .
   [jjtree] File "/home/tom/javacc/javacc/examples/JJTreeExamples/eg2/Node.java" does not exist.  Will create one.
   [jjtree] File "/home/tom/javacc/javacc/examples/JJTreeExamples/eg2/SimpleNode.java" does not exist.  Will create one.
   [jjtree] File "/home/tom/javacc/javacc/examples/JJTreeExamples/eg2/ASTStart.java" does not exist.  Will create one.
   [jjtree] File "/home/tom/javacc/javacc/examples/JJTreeExamples/eg2/ASTAdd.java" does not exist.  Will create one.
   [jjtree] File "/home/tom/javacc/javacc/examples/JJTreeExamples/eg2/ASTMult.java" does not exist.  Will create one.
   [jjtree] File "/home/tom/javacc/javacc/examples/JJTreeExamples/eg2/ASTInteger.java" does not exist.  Will create one.
   [jjtree] Annotated grammar generated successfully in /home/tom/javacc/javacc/examples/JJTreeExamples/eg2/eg2.jj
   [javacc] Java Compiler Compiler Version 3.2 (Parser Generator)
   [javacc] (type "javacc" with no arguments for help)
   [javacc] Reading from file /home/tom/javacc/javacc/examples/JJTreeExamples/eg2/eg2.jj . . .
   [javacc] File "TokenMgrError.java" does not exist.  Will create one.
   [javacc] File "ParseException.java" does not exist.  Will create one.
   [javacc] File "Token.java" does not exist.  Will create one.
   [javacc] File "SimpleCharStream.java" does not exist.  Will create one.
   [javacc] Parser generated successfully.
    [javac] Compiling 16 source files to /home/tom/javacc/javacc/examples/JJTreeExamples/eg2
     [echo] *******
     [echo] ******* Now cd into the eg2 directory and run 'java eg2' ******
     [echo] *******

BUILD SUCCESSFUL
Total time: 3 seconds
[tom@hal JJTreeExamples]$ cd eg2
[tom@hal eg2]$ java eg2
Reading from standard input...
(a + b) * (c + 1);
Start
 Mult
  Add
   Identifier: a
   Identifier: b
  Add
   Identifier: c
   Integer
Thank you.

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.