Best way to create an empty map in Java

Question

I need to create an empty map   if  fileParameters    null      fileParameters    HashMap lt String  String gt   Collections EMPTY MAP    The problem is that the above code produces this warning   Type safety  Unchecked cast from Map to HashMap  What is the best way to create this empty map

User · Answer

The emptyMap method of the Collections class

User · Answer

Since in many cases an empty map is used for null-safe design  you can utilize the nullToEmpty utility method   class MapUtils      static  lt K V gt  Map lt K V gt  nullToEmpty Map lt K V gt  map        if  map    null          return map        else          return Collections  lt K V gt emptyMap       or guava ImmutableMap of                    Similarly for sets   class SetUtils      static  lt T gt  Set lt T gt  nullToEmpty Set lt T gt  set        if  set    null          return set        else         return Collections  lt T gt emptySet                   and lists   class ListUtils      static  lt T gt  List lt T gt  nullToEmpty List lt T gt  list        if  list    null          return list        else         return Collections  lt T gt emptyList

User · Answer

1  If the Map can be immutable   Collections emptyMap       or  in some cases  Collections  lt String  String gt emptyMap     You ll have to use the latter sometimes when the compiler cannot automatically figure out what kind of Map is needed  this is called type inference   For example  consider a method declared like this        public void foobar Map lt String  String gt  map           When passing the empty Map directly to it  you have to be explicit about the type   foobar Collections emptyMap                        doesn t compile foobar Collections  lt String  String gt emptyMap        works fine   2  If you need to be able to modify the Map  then for example   new HashMap lt String  String gt       as tehblanx pointed out     Addendum  If your project uses Guava  you have the following alternatives   1  Immutable map   ImmutableMap of      or  ImmutableMap  lt String  String gt of     Granted  no big benefits here compared to Collections emptyMap    From the Javadoc      This map behaves and performs comparably to Collections emptyMap      and is preferable mainly for consistency and maintainability of your   code    2  Map that you can modify    Maps newHashMap      or  Maps  lt String  String gt newHashMap     Maps contains similar factory methods for instantiating other types of maps as well  such as TreeMap or LinkedHashMap     Update  2018   On Java 9 or newer  the shortest code for creating an immutable empty map is   Map of        using the new convenience factory methods from JEP 269

User · Answer

If you need an instance of HashMap  the best way is   fileParameters   new HashMap lt String String gt       Since Map is an interface  you need to pick some class that instantiates it if you want to create an empty instance  HashMap seems as good as any other - so just use that

User · Answer

Collections emptyMap

User · Answer

What about    Map lt String  String  s   Collections emptyMap

User · Answer

Either Collections emptyMap    or if type inference doesn t work in your case  Collections  lt String  String gt emptyMap

[java] Best way to create an empty map in Java

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