Dynamically adding elements to ArrayList in Groovy

Question

I am new to Groovy and  despite reading many articles and questions about this  I am still not clear of what is going on  From what I understood so far  when you create a new array in Groovy  the underlying type is a Java ArrayList  This means that it should be resizable  you should be able to initialize it as empty and then dynamically add elements through the add method  like so   MyType   list      list add new MyType         This compiles  however it fails at runtime  No signature of method   LMyType  add   is applicable for argument types   MyType  values   MyType 383bfa16   What is the proper way or the proper type to do this

User · Accepted Answer

The Groovy way to do this is  def list      list  lt  lt  new MyType        which creates a list and uses the overloaded leftShift operator to append an item  See the Groovy docs on Lists for lots of examples

User · Answer

What you actually created with   MyType   list        Was fixed size array  not list  with size of 0  You can create fixed size array of size for example 4 with   MyType   array   new MyType 4    But there s no add method of course    If you create list with def it s something like creating this instance with Object  You can read more about def here   And    creates empty ArrayList in this case   So using def list      you can then append new items with add   method of ArrayList  list add new MyType      Or more groovy way with overloaded left shift operator   list  lt  lt  new MyType

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