Map with Key as String and Value as List in Groovy

Question

Can anyone point me to an example of how to use a Map in Groovy which has a String as its key and a List as value

User · Answer

def map       map  stringKey      1  2  3  4  map  anotherKey      55  66  77   assert map  anotherKey       55  66  77

User · Answer

Groovy accepts nearly all Java syntax  so there is a spectrum of choices  as illustrated below      Java syntax   Map lt String List gt  map1    new HashMap lt  gt     List list1   new ArrayList    list1 add  hello    map1 put  abc   list1    assert map1 get  abc      list1      slightly less Java-esque  def map2    new HashMap lt String List gt    def list2   new ArrayList   list2 add  hello   map2 put  abc   list2  assert map2 get  abc      list2     typical Groovy  def map3        def list3      list3  lt  lt   hello  map3  abc   list3 assert map3  abc     list3

User · Answer

One additional small piece that is helpful when dealing with maps list as the value in a map is the withDefault Closure  method on maps in groovy  Instead of doing the following code   Map m       for object in listOfObjects      if m containsKey object myKey           m get object myKey  add object myValue        else         m put object myKey   object myValue          You can do the following   Map m       withDefault key - gt  return     for object in listOfObjects      List valueList   m get object myKey    m put object myKey  valueList      With default can be used for other things as well  but I find this the most common use case for me   API  http   www groovy-lang org gdk html   Map -  withDefault Closure

User · Answer

Joseph forgot to add the value in his example with withDefault  Here is the code I ended up using   Map map       withDefault   key - gt  return      listOfObjects each   map get it myKey  add it myValue

User · Answer

you don t need to declare Map groovy internally recognizes it   def personDetails    firstName  John   lastName  Doe   fullName  John Doe       print the values       println  First Name    personDetails firstName       println  Last Name    personDetails lastName     http   grails asia groovy-map-tutorial

[groovy] Map with Key as String and Value as List in Groovy

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