An error occurred while calling z:java.nio.file.Path.of. Method of([class java.lang.String]) does not exist

[Siddharth Jain]

hello

i am trying to create a Path object like this:

>>> gateway.jvm.java.nio.file.Path.of(file)

and get this error:

py4j.protocol.Py4JError: An error occurred while calling z:java.nio.file.Path.of. Trace:
py4j.Py4JException: Method of([class java.lang.String]) does not exist
at py4j.reflection.ReflectionEngine.getMethod(ReflectionEngine.java:321)
at py4j.reflection.ReflectionEngine.getMethod(ReflectionEngine.java:342)
at py4j.Gateway.invoke(Gateway.java:276)
at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:132)
at py4j.commands.CallCommand.execute(CallCommand.java:79)
at py4j.GatewayConnection.run(GatewayConnection.java:238)
at java.base/java.lang.Thread.run(Thread.java:1623)

for reference java.nio.file.Path.of(file) does work in Java and the method is documented here. So why is py4j complaining and how can I fix this? thanks.

[Jonah Graham]

Hi,

The issue is that Path.of(String) method doesn't actually exist, your link was to Path.of(String, String...) which is syntactic sugar for a method with a signature of Path.of(String, String[]). So when you try to call Path.of(String) py4j correctly reports that there is no such method.

Therefore you need to pass an empty array as the second parameter like this:

>>> p = gateway.jvm.java.nio.file.Path.of("/tmp/my/../path", gateway.new_array(gateway.jvm.java.lang.String, 0))

And then you can call methods on p as expected.
>>> p.normalize().toString()
'/tmp/path'
>>> p.toString()
'/tmp/my/../path'

It follows that you can't do this either as there is no method with that signature either:

>>> p = gateway.jvm.java.nio.file.Path.of("/part1", "part2", "part3", "part4")

Instead do this:

>>> more = gateway.new_array(gateway.jvm.java.lang.String, 3)
>>> more[0] = "part2"
>>> more[1] = "part3"
>>> more[2] = "part4"
>>> p = gateway.jvm.java.nio.file.Path.of("/part1", more)
>>> p.toString()
'/part1/part2/part3/part4'

To slightly complicate matters, Java collections actually does have a List.of(E) method, and List.of(E, E), and List.of(E, E, E), etc and finally List.of(E[]). Which means you need to know a bit more details about the APIs when calling from Python than you would if you used Java directly:

>>> p = gateway.jvm.java.util.List.of("/part1", "part2", "part3", "part4")
>>> p.toString()
'[/part1, part2, part3, part4]'

But if you want to call the List.of(E[]) version you need to use an Object array:

>>> more = gateway.new_array(gateway.jvm.java.lang.Object, 3)
>>> more[0] = "part2"
>>> more[1] = "part3"
>>> more[2] = "part4"
>>> p = gateway.jvm.java.util.List.of(more)
>>> p.toString()
'[part2, part3, part4]'

HTH

Jonah

~~~
Jonah Graham (he/him)
Kichwa Coders
www.kichwacoders.com

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