Collections

Lists

[item1, item2, ...]

• The list items are separated by commas within brackets.
• To create an empty list, assign empty brackets to a reference.

Maps

[key1: value1, key2: value2, ...]

• Syntax: a comma-separate list of key/value pairs in brackets.
• Each key is separated from its value by a colon.
• To create an empty map, assign brackets containing only a colon, [:], to a reference.
• There are at least 5 ways to add an item to a map, including bracket notation (e.g., map['item1'] = 'Hi!'), shown below.

Bracket Notation

You can add values to or retrieve values from a Groovy map with bracket notation, just like JavaScript objects:

// Here is an example map declaration with initial values 
def personAgeMap = [matthew: 30, mark:25, luke: 40]

// Since Groovy is just a superset of Java, we can use the put method to add an entry to a map. 
personAgeMap.put('john', 41)

// We can also use bracket notation. For example: 
personAgeMap['Tim'] = 28

// Another way is to treat the key as property of the map object. Example: 
personAgeMap.Roy = 32

// You can also use dot (.) followed by the key enclosed in quotes. Example: 
personAgeMap.'Tim' = 55

// Lastly, you can add entries coming from another map. You can push entries from one map to another, for example:
personAgeMap << [Michael:29]

References

• http://grails.asia/groovy-add-to-map