How to dynamically create a Java class List?

Question

I am using groovy 1.8 where i want to have a list something like this
List<MyQueryClass> queryl=new List<MyQueryClass>()
So that using the below loop i can add more to this list, how can I do that?

def queryxml=new XmlSlurper().parse(QueryProvider.class.getResourceAsStream( '/queries.xml' ))
    queryxml.query.each { node ->
        operation="${[email protected]()}"
        if(operation.equals(op.create.toString()))
        {
            query="${node.text()}"
            println "$query"
            MyQueryClass myQuery=new MyQueryClass (query)
            queryl.add(myQuery)
        }           
    }

where did you define queryl? this seems that it should be working if you define queryl above queryxml... what error do you get? — draganstankovic
– draganstankovic, Commented May 26, 2011 at 10:30
I define queryl above this code, when i write List<MyQueryClass> queryl=new List<MyQueryClass>() i get Groovy:You cannot create an instance from the abstract interface 'java.util.List' error — AabinGunz
– AabinGunz, Commented May 27, 2011 at 4:46

AabinGunz · Accepted Answer · 2011-05-26 10:56:07Z

3

My apologies, I could not convey my question properly.
I figured it out, as I cannot create an instance out of a abstract interface java.util.List

List<MyQueryClass> queryl=new ArrayList<MyQueryClass>()

does the work. Thanks tim and draganstankovic

answered May 26, 2011 at 10:56

AabinGunz

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Comments

tim_yates · Accepted Answer · 2011-05-26 10:33:00Z

1

You don't give us much to go on, but assuming you have a class:

@groovy.transform.Canonical class MyQuery {
  String queryText
}

And your XML is similar to:

def xml = '''<xml>
  <query operation="create">
    This is q1
  </query>
  <query operation="q2">
    This is q2
  </query>
  <query operation="create">
    This is q3
  </query>
</xml>'''

Then you should be able to use findAll to limit the xml to just the nodes of interest, followed by collect to build up your list of objects like so:

def queryxml = new XmlSlurper().parseText( xml )

List<MyQuery> query = queryxml.query.findAll { node ->  // Filter the nodes
  [email protected]() == 'create'
}.collect { node ->                                     // For each matching node, create a class
  new MyQuery( node.text().trim() )
}

println query

And that prints out:

[MyQuery(This is q1), MyQuery(This is q3)]

PS: The groovy.transform.Canonical annotation is explained here

answered May 26, 2011 at 10:33

tim_yates

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4 Comments

AabinGunz Over a year ago

I think somewhere I was not able to question properly, B4 I was doing something like List<MyQueryClass> queryl=new List<MyQueryClass>[5] and once i added I got 6 as its size, but actually only 1 query was getting added, so my question was how to do it dynamically, I figured it out, as I cannot create an instance out of a abstract interface java.util.List So finally i did List<MyQueryClass> queryl=new ArrayList<MyQueryClass>() to make it work :) Thanks though for answering, I'll give you an up for giving an answer

tim_yates Over a year ago

@Abhishek As you're using groovy, you shouldn't need to do new ArrayList<MyQueryClass>() at all...

AabinGunz Over a year ago

what should I be using instead, because if i use List<MyQueryClass> queryl=new List<MyQueryClass>() i get an error mark where it says Groovy:You cannot create an instance from the abstract interface 'java.util.List'

tim_yates Over a year ago

@Abhishek Have you looked at the code I posted? That generates a list from the collect call. Or, you could just do: List<MyQueryClass> queryl = [] which does the same as your line of code.

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