defaultMatcherFactory is Null in utils.Registry$Factory.instantiate(Object[])

[Fuzanwenn]

Hello, I am getting the following error for the matcher. Basically the matcher could not use because I did not register a matcher?

Cannot invoke "com.github.gumtreediff.utils.Registry$Factory.instantiate(Object[])" because "this.defaultMatcherFactory" is null java.lang.NullPointerException: Cannot invoke "com.github.gumtreediff.utils.Registry$Factory.instantiate(Object[])" because "this.defaultMatcherFactory" is null

This is my code, which is just taken from Wiki.

Run.initGenerators();
val srcFile = "src/test/kotlin/data/Duke.java"
val dstFile = "src/test/kotlin/data/Command.java"
val src: Tree = TreeGenerators.getInstance().getTree(srcFile).root // retrieves and applies the default parser for the file
val dst: Tree = TreeGenerators.getInstance().getTree(dstFile).root // retrieves and applies the default parser for the file
val defaultMatcher = Matchers.getInstance().getMatcher() // retrieves the default matcher
val mappings: MappingStore = defaultMatcher.match(src, dst) // computes the mappings between the trees

Hope someone could kindly help me out. Much appreciated!

[jrfaller]

Hi!

I am afraid but (converted to Java) this code works for me. Maybe this is a class path issue? How do you launch the program?

[Fuzanwenn]

Hi thank you so much for your reply!

I am using Gradle in Kotlin to install GumTree 3.0.0 and directly running the code above as a Unit Test.
implementation("com.github.gumtreediff:core:3.0.0")
implementation("com.github.gumtreediff:client:3.0.0")
implementation("com.github.gumtreediff:gen.jdt:3.0.0")
implementation("fr.inria.gforge.spoon.labs:gumtree-spoon-ast-diff:1.100")

I am guessing maybe the problem is because I did not install all the prerequisites, for which I have installed 2 (out of 5)? However, I see that the prerequisites are mainly for using the parser. I am able to use the Parser but not the Matcher. The error message shows that there seems to be a problem with the initialization of Matchers. So I don't think missing certain prerequisities caused the error here?

May I ask for a detailed explanation of the error message? I am currently not sure what caused the error.

By the way, may I ask if there is any pretty-print function for GumTree 2.1.0? Because I actually have no issue using GumTree 2.1.0, but I could not find a pretty-print function for that version. And what I need most is a tool which can convert AST back to the source code.

Thank you so much again for your help and support!

[jrfaller]

I recommend using the last version 4.0.0-beta3.

The external dependencies are not required in order to diff Java code.

The error indicates that GumTree's registry is not able to retrieve the default diff algorithm and instead return a null value.

Using GumTree it's unfortunately impossible to convert back ASTs to source code. However there is https://mvnrepository.com/artifact/fr.inria.gforge.spoon.labs/gumtree-spoon-ast-diff which is specially done for this purpose.

Cheers!