Java Tree parser output for ANTLR

abstract-syntax-tree, antlr, java, tree

Solution

I've found a sample template in the ANTLR website, its the Javatreeparser.g, which the site says could produce the AST that I need,

No, the combined grammar `Java.g` from the ANTLR wiki produces a lexer and parser for Java source files. The parser then constructs an AST of this source and this AST can then be used by `JavaTreeParser.g` to traverse it. The tree grammar `JavaTreeParser.g` is not used to create an AST. This is done by the parser created from `Java.g`.

What I've done so far is placing the grammar file together with my existing java grammar.

That is incorrect. The tree grammar `JavaTreeParser.g` expects an AST as input that the parser generated from `Java.g` produced. You can't just plug in another parser (or other tree grammar, for that matter).

But I have no idea on how to use and output the AST that I need from the file. How do I do it?

See this previous Q&A: Visualizing an AST created with ANTLR (in a .Net environment)

EDIT

I didn't want to post this immediately, because I wanted you to give it a try yourself first (yes, I'm mean!) ;)

Here's a quick demo:

- copy the `Java.g` in a directory and remove the `@header{...}` and `@lexer:::header{...}` declarations from it;

- copy `antlr-3.3.jar` into the same directory;

- create the files `Main.java` and `Test.java` in this directory (see below).

Test.java

public class Test {

    int i = 1 + 2;
    String s;

    Test(String s) {
        this.s = s;
    }
}

Main.java

import org.antlr.runtime.*;
import org.antlr.runtime.tree.*;
import org.antlr.stringtemplate.*;

public class Main {
    public static void main(String[] args) throws Exception {
        JavaLexer lexer = new JavaLexer(new ANTLRFileStream("Test.java"));
        JavaParser parser = new JavaParser(new CommonTokenStream(lexer));
        CommonTree tree = (CommonTree)parser.javaSource().getTree();
        DOTTreeGenerator gen = new DOTTreeGenerator();
        StringTemplate st = gen.toDOT(tree);
        System.out.println(st);
    }
}

Now generate a lexer and parser:

java -cp antlr-3.3.jar org.antlr.Tool Java.g 

Then compile all `.java` source files:

javac -cp antlr-3.3.jar *.java 

And finally run the `Main` class and pipe the output to a file called `ast.dot`.

java -cp .:antlr-3.3.jar Main > ast.dot

(on Windows, do: `java -cp .;antlr-3.3.jar Main > ast.dot`)

If you now open the file `ast.dot`, you see a DOT representation of the AST produced by the parser. You can visualize this AST by copy-pasting the DOT-source in here: http://graphviz-dev.appspot.com resulting in the following image:

Problem

Original source

Related problems

• Visualizing an AST created with ANTLR (in a .Net environment)