Groovy: Confusion about Map Reassign via `getOrDefault` - groovy

Question

I'm going to initialize a empty Map dynamically in a loop, i.e. key1 and key2 are variables in the loop:
Map<String, Map<String, List>> map = [
key1: [
key2: []
]
]
I'm trying initialize the map structure by getOrDefault in two ways. One (y) using the hardcode as key name, another (x) using the variable as the keyname:
Map y = [:]
Map x = [:]
String b = 'b'
String c = 'c'
y = y.getOrDefault( "b" , [ "b" : [:] ] )
.getOrDefault( "c" , [ "b" : [ "c" : []] ] )
x = x.getOrDefault( "${b}" , [ "${b}" : [:] ] )
.getOrDefault( "${c}" , [ "${b}" : [ "${c}" : []] ] )
However, when I try get result of map.b.c,
Map x:
x.get("${b}").get("${c}") : works
x["${b}"]["${c}"] : java.lang.NullPointerException
Map y works well in all various ways
println """
y['b']['c'] : ${y['b']['c']}
y.b.c : ${y.b.c}
y.get('b').get('c') : ${y.get('b').get('c')}
x.get("\${b}") : ${x.get("${b}")}
x["\${b}"] : ${x["${b}"]} // *why null*
x.get("\${b}").get("\${c}") : ${x.get("${b}").get("${c}")}
"""
println """ x["\${b}"]["\${c}"] : ${x["${b}"]["${c}"]} """
==> result
y['b']['c'] : []
y.b.c : []
y.get('b').get('c') : []
x.get("${b}") : [c:[]]
x["${b}"] : null // *why null*
x.get("${b}").get("${c}") : []
Exception thrown
java.lang.NullPointerException: Cannot get property 'c' on null object
at ConsoleScript77.run(ConsoleScript77:21)
I want to know why x.get("${b}").get("${c}") works, but x["${b}"]["${c}"] got null
btw, here the dynamic map initialization details:
Map m = [
'x' : [
'name': 'x',
'size': ['1', '2'],
'age': '1',
],
'y': [
'name': 'x',
'size': ['2', '3'],
'age': '2'
]
]
Map a = [:]
m.each{ k, v ->
v.size.each {
String t = "${v.name}-${it}"
a = a.getOrDefault(t, ["${t}": [:]])
println """
t: ${t}
k: ${k}
a: ${a}
a.t: ${a.t}
a.get("${t}"): ${a.get("${t}")}
a["${t}"]: ${a["${t}"]}
"""
}
}
=== output:
t: x-1
k: x
a: [x-1:[:]]
a.t: null
a.get("x-1"): [:]
a["x-1"]: null
t: x-2
k: x
a: [x-2:[:]]
a.t: null
a.get("x-2"): [:]
a["x-2"]: null
....

Answer 1

Appreciate #daggett.
So the truth is:
y.each { k, v ->
println """
key: ${k} \t\t\t key.getClass(): ${k.getClass()}
value: ${v} \t\t value.getClass(): ${v.getClass()}
"""
}
x.each { k, v ->
println """
key: ${k} \t\t\t key.getClass(): ${k.getClass()}
value: ${v} \t\t value.getClass(): ${v.getClass()}
"""
}
==> result
key: b key.getClass(): class java.lang.String
value: [c:[]] value.getClass(): class java.util.LinkedHashMap
key: b key.getClass(): class org.codehaus.groovy.runtime.GStringImpl
value: [c:[]] value.getClass(): class java.util.LinkedHashMap
So, according to my previous ${x["${b}"]}, the key of x ( "${b}" ) was type conversion to String, and x only has the key belongs to GStringImpl, so the result is null
However, .get("${b}") works, because of :
println "${b}".getClass() // class org.codehaus.groovy.runtime.GStringImpl
Here more details:
Map x = [:]
String str = 'a'
x = x.getOrDefault( "${str}", [ "${str}" : [:] ] )
x.each { k, v -> println "${k}: ${k.getClass()}" }
Map x = [:]
String str = 'a'
x = x.getOrDefault( "${str}", [ "${str}" : [:] ] )
x.each { k, v -> println "${k}: ${k.getClass()}" } // a: class org.codehaus.groovy.runtime.GStringImpl
assert x == [ "${s}" : [:] ]
assert x.a == null
assert x."${str}" == null
assert x["${str}"] == null
assert x[str] == null
assert x.get(str) == null
assert x.get("${str}") == [:]