java - Adding generic types to EnumMap -

i'm trying add instances following enummap:

class activeg<d extends gdata, t extends gtemplate> {      enummap<gstatetype, gstate<activeg<d,t>> map;     ..     .. }  class tgdata extends gdata {...} class tgtemplate extends gtemplate {....}  class activetg extends activeg<tgdata, tgtemplate> {      // fails compilation error     super.states.put(gstatetype.waiting, new tgwaitingstate<activetg>(this));     ...     ... } 

the error get:

the method put(gstatetype, gstate<activeg<tgdata,tgtemplate>>) in type enummap<gstatetype,gstate<activeg<tgdata,tgtemplate>>> not  applicable arguments (gstatetype, tgwaitingstate<activetg>) 

can try me figure out what's missing make work?? thanks!

in brief, generics in java not covariance.

e.g. if have

class parent {...}  class child extends parent {...} 

foo<child> not foo<parent>

go code:

your enum map in activetg expecting gstate<activeg<tgdata,tgtemplate>> value, giving tgwaitingstate<activetg>, gstate<activetg>.

although activetg is-a activeg<tgdata,tgtemplate>, gstate<activetg> not gstate<activeg<tgdata,tgtemplate>>.

in order solve it, need quite change in type params,

class activeg<d extends gdata,                t extends gtemplate,                e extends activeg<d,t>> {      enummap<gstatetype, gstate<e>> map; } 

or make map type enummap<gstatetype, gstate<? extends activeg<d,t>>. may not work in situation, example, need retrieve result gstate<activetg> instead of gstate<activeg<d,t>>