java - Breaking cyclic dependency in constructor -

i'm writing java class manage hex map (class gamemapimpl implements gamemap) contains cell objects. cell objects saved in hashmap<hex,cell>, key position on hex map.

the whole thing used tightly coupled between cells , gamemap, cyclic dependency between two, i'm trying refactor allow more easy testing.

(code below simplified)

public interface gamemap {     void hascell(hex hex);     void getcell(hex hex); }  class gamemapimpl implements gamemap {     private map<hex, cell> cellmap;      gamemapimpl(set<cell> cells) {         cellmap = new hashmap<>();         (cell cell : cells) {             // check conditions on cells             // ensure map correct, e.g. 1 cell             // of particular type              // ensures cellmap key cell's position.             cellmap.put(cell.position(), cell);         }     }      //obvious implementation hascell , getcell methods } 

each cell needs have hex position field can own position in gamemap. in addition, cell objects need have reference owning gamemap, perform common useful operations such looking neighbours.

public class cell {     final hex position;     final gamemap gamemap;      cell(hex position, gamemap gamemap) {         this.position = position;         this.gamemap = gamemap;     }      public set<cell> getneighbours() {         //perform operation needs both gamemap , position     } } 

the gamemap built in gamemapbuilder, provides set<cell> gamemap constructor.

public class gamemapbuilder {     public gamemap build(...) { // args omitted simplicity          set<cells> cells = new hashset<>();         (... : ...)         {             hex position = calculateposition(...);             cell cell = new cell(position, gamemap);         }         gamemap gamemap = new gamemap(cells);         return gamemap;     } } 

as can see, last snippet of code wrong, because i'm referencing non-existent gamemap variable. here lies problem: if create gamemap after initializing cells, cannot pass in cell's constructor. if opposite, cannot pass set<cells> gamemap in order initialize correctly.

does more experienced programmer have idea on how decouple correctly these 2 classes?

alternatively, can go previous tightly coupled design , assume cells exist when gamemap creates them. being these small objects , contained in same package, wouldn't big of deal.

use setter passing gamemap cell not constructor. can make package-protected hide other code , call setter in gamemap constructor or in loop in gamemapbuilder. known de-frameworks use setters solve circular dependencies.