CODEWITHSUNDEEP
oopgroovy
cspeter8
cspeter8

Reputation: 101

In Groovy, if class is not called why instantiation exception?

When I execute the following experimental code subset at http://groovyconsole.appspot.com/

class FileHandler {
    def rootDir

    FileHandler(String batchName) {
        rootDir = '.\\Results\\'+batchName+'\\'
    }
}

//def fileHandler = new FileHandler('Result-2012-12-15-10-48-55')

An exception results:

java.lang.NoSuchMethodException: FileHandler.<init>()

When I uncomment the last line that instantiates the class, the error goes away.

Can someone explain why this is? I'm basically attempting to segregate the definition and instantiation of the class into 2 files to be evaluated separately. Thanks

Upvotes: 1

Views: 771

Answers (1)

Brian Henry
Brian Henry

Reputation: 3171

I'm not sure of the exact implementation details behind http://groovyconsole.appspot.com/ (source linked to from there points to Gaelyk, which I've not looked over). I'd bet it's looking for a no-arg constructor for the class you've presented, in an effort to find something runnable. (note that if you provide that, it still won't work, as it wants a main() :/)

Running locally in groovyConsole will die a bit sooner, with the following error message:

groovy.lang.GroovyRuntimeException: This script or class could not be run. It should either:
- have a main method,
- be a JUnit test or extend GroovyTestCase,
- implement the Runnable interface,
- or be compatible with a registered script runner.

This is perhaps more descriptive and to the point. If you want to run some Groovy as a simple script, you'll need to supply a jumping-in point. The easiest way is an executable statement in your groovy file, outside of any class definition (e.g, uncommenting your instantiation statement). Alternatively, a class with a main method should do it. (see here).

If 2 files is how you want to break it up, you can save the class file def in one groovy file (e.g., First.groovy) and create a second (e.g., Second.groovy) with just your executable statements. (I believe the first one will be in the classpath automatically when you run groovy Second, if both are in same directory)

Upvotes: 2

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