Maps
Maps are similar to lists, but they assign each value to a key. Meaning instead of accessing the value by the index, you can get it by using the key. There can only be one value for a given key, but multiple keys can have the same value.
There different types of maps. Java's default map is HashMap. It doesn't keep the elements order causing the elements to be seemingly random.
The key and value can be of different types. If the key is a string you can leave out the ' or ".
def simpleMap = [:] // a empty ordered hash map
def hashMap = new HashMap() // a empty unordered hash map
// this maps the short form of some periodic elements to their real name
def elements = [
Au: 'Gold',
Ag: 'Silver',
Pb: 'Lead',
H: 'Hydrogen'
]Getting values
We are using the map we created above here.
println(elements['Pb']) // Lead
println(elements['Ag']) // Silver
println(elements['B']) // null since there is no key 'B'Modifying maps
We are using the map we created above here.
elements['Au'] = 'Copper' // Au is now mapped to copper
elements.remove('H') // removes H: HydrogenVariable keys
Groovy can have the keys of a map be set via variables. However, in order to do this, the key might need to be surrounded in parentheses to be properly handled.
This is particularly relevant with GroovyScript Object Mappers.
def itemStackToValue = [
(item('minecraft:dirt')): -1,
(item('minecraft:stone')): 5,
(item('minecraft:clay')): 1000,
]Warning
Failing to properly surround a key in parentheses if it requires them may result in the script file throwing a MultipleCompilationErrorsException due to being "unable to resolve class".
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