java - How to force instantiation of static fields -

i quite surprised of output of following code:

country class

public class country {      private static map<string, country> countries = new hashmap<string, country>();      private final string name;      @suppresswarnings("leakingthisinconstructor")     protected country(string name) {         this.name = name;         register(this);     }      /** country name */     public static country getcountry(string name) {         return countries.get(name);     }      /** register country map */     public static void register(country country) {         countries.put(country.name, country);     }      @override     public string tostring() {         return name;     }      /** countries in europe */     public static class europecountry extends country {          public static final europecountry spain = new europecountry("spain");         public static final europecountry france = new europecountry("france");          protected europecountry(string name) {             super(name);         }     }  } 

main method

system.out.println(country.getcountry("spain")); 

output

null

is there clean way of forcing class extend country loaded countries map contains country instances?

yes, use static initializer block:

public class country {      private static map<string, country> countries = new hashmap<string, country>();      static {         countries.put("spain", new eurocountry("spain"));      }  ...