I understand that groovy uses java.util.ArrayList to represent objects created using array literals like so: arr = []. I wanted to understand what underlying object groovy uses to create a map created like so: my_map = [:]. I wrote this code below:
7 array = []
8 array[1] = 'a'
9 array[2] = 'b'
10 println array.class.name
11 println array
12
13 my_map = [:]
14 my_map['OK'] = 200
15 println my_map.class
16 println my_map
The output produced by code above is:
java.util.ArrayList
[null, a, b]
null
[OK:200]
Notice the .class attribute is missing on my_map. Why is this happening?
>Solution :
my_map is a Map. In groovy map.key is a convenience to get the value associated with the key from the map.
The issue here is that it’s looking for a key named class, and there isn’t one.
To get the class of a Map, you need to explicitly ask for it with my_map.getClass()