Overriding Java methods defined with the same name

Ruby JRuby
1

Hi,

I’m trying to replicate the example from
http://code.google.com/p/javaparser/wiki/UsingThisParser#Visiting_class_methods
in Jruby.

In the original example, the abstract class VoidVisitorAdapter defines
various ‘visit’ methods that accept different inputs
(AnnotationDeclaration, CompilationUnit, MethodDeclaration, etc.)

Check the source of VoidVisitorAdapter here for reference:
http://code.google.com/p/javaparser/source/browse/trunk/JavaParser/src/japa/parser/ast/visitor/VoidVisitorAdapter.java

My code in JRuby is:

require ‘java’
require ‘javaparser-1.0.8.jar’

java_import Java::japa.parser.JavaParser
java_import Java::japa.parser.ast.CompilationUnit
java_import Java::japa.parser.ast.body.MethodDeclaration
java_import Java::japa.parser.ast.visitor.VoidVisitorAdapter
java_import java.io.FileInputStream

class MethodVisitor < VoidVisitorAdapter
# I’m trying to Override the method with the following signature:
# public void visit(MethodDeclaration n, Object arg)
# How can it be done in JRuby ??
def visit(n, arg)
puts(n.get_name)
end
end

fis = FileInputStream.new(ARGV[0])

begin
cu = JavaParser.parse(fis)
rescue Exception => err
puts err
ensure
fis.close
end

mv = MethodVisitor.new
mv.java_send :visit, [CompilationUnit, java.lang.Object], cu, nil

The trouble I’m facing is overriding the ‘visit’ method that accepts
MethodDeclaration. How can this be achieved in JRuby when there are
multiple definitions of methods with same name?

– Manish

2

On Thu, Sep 9, 2010 at 1:34 PM, Manish Ss [email protected] wrote:

Check the source of VoidVisitorAdapter here for reference:
java_import Java::japa.parser.ast.body.MethodDeclaration
end
end

mv = MethodVisitor.new
mv.java_send :visit, [CompilationUnit, java.lang.Object], cu, nil

The trouble I’m facing is overriding the ‘visit’ method that accepts
MethodDeclaration. How can this be achieved in JRuby when there are
multiple definitions of methods with same name?

Your ‘def visit’ above will override all visit overloads because Ruby
has no way of using types to specify a particular overload. So your
visit method will need to look at the arguments provided and then use
java_send to delegate it to the proper base class version when you
don’t actually want to handle that particular version of the visit
method. So some plumbing…this does seem like an interesting
enhancement to JI though. The ability to override some overloads of
the same method name. Anyone have any ideas on what this could look
like?

Java.override [CompilationUnit, :object]
def visit(a, b)
end

???

-Tom

–
blog: http://blog.enebo.com twitter: tom_enebo
mail: [email protected]

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3

Thomas E Enebo wrote:

On Thu, Sep 9, 2010 at 1:34 PM, Manish Ss [email protected] wrote:

Check the source of VoidVisitorAdapter here for reference:
java_import Java::japa.parser.ast.body.MethodDeclaration
� �end
end

mv = MethodVisitor.new
mv.java_send :visit, [CompilationUnit, java.lang.Object], cu, nil

The trouble I’m facing is overriding the ‘visit’ method that accepts
MethodDeclaration. How can this be achieved in JRuby when there are
multiple definitions of methods with same name?

Your ‘def visit’ above will override all visit overloads because Ruby
has no way of using types to specify a particular overload. So your
visit method will need to look at the arguments provided and then use
java_send to delegate it to the proper base class version when you
don’t actually want to handle that particular version of the visit
method.

Ahh I get it (damn!.. silly me).
Thanks for the reply Tom. Here is my modified MethodVisitor class:

class MethodVisitor < VoidVisitorAdapter
# This method will now check for MethodDeclaration
# and process it
def visit(n, arg)
super
klass = n.class

  if klass.eql?(Java::JapaParserAstBody::MethodDeclaration)
    self.java_send :visit, [MethodDeclaration, java.lang.Object], n,

arg
puts("Method: " + n.get_name)
end
end
end

This works nicely :slight_smile: … thanks.
But is this a good way to do it? Is there a better way ??

So some plumbing…this does seem like an interesting
enhancement to JI though. The ability to override some overloads of
the same method name. Anyone have any ideas on what this could look
like?

Java.override [CompilationUnit, :object]
def visit(a, b)
end

???

Something similar to java_alias, java_send, java_anotation,
java_signature, etc. would be nice:

class MethodVisitor

java_override :visit, [MethodDeclaration, :object]
def visit(n, arg)
# some code …
end
end

-Tom

–
blog: http://blog.enebo.com� � �� twitter: tom_enebo
mail: [email protected]

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