java - Give a reference to forming object from created object -

what best way following:

i have class a, creates , holds objects class b. object of class b doing own things, , has call method of parent object (of class a). heard not best idea hold reference of object in object b (idea shown in code snippet).

class a{     private b objectb;     public a(){         objectb = new b(this);     }     public void methoda(){         // [...]     } }  class b{     private objecta;     public b(a objecta){         this.objecta = objecta;     }     public void methodb(){         // [...] stuff        objecta.methoda();     } } 

is bad approach this? there better way?

as far can see class b acts sort of proxy or decorator difference , b don't share common interface. if design requires class b act (proxy, decorator, ...) best way define common interface: b implements a's interface , can "impersonate" it: in these cases, sharing reference "proxyed" class not bad, required. e.g.:

public interface {  void methoda(); } public class aimpl implements {   @override   public void methoda() { /* .... */ } } public class aproxy implements {   private final a; // use interface not implementation   public aproxy(final a)  { this.a = a; }   @override   public void methoda() {      /* .... */      a.methoda();      /* .... */   } } 

the other approach define hierarchy in parent of b b "needs" know work, or conversely , b have 1 1 e-r dependency: can follow composite design pattern - abused on orm techniques - or dependency injection pattern. in orm techniques parents , children have reference of each other act independently each other.

// might @entity public class {    private b child;    /* setter , getter */ }  // might @entity public class b {    private parent;    /* setter , getter */ } 

in dependency injection have options enforce relationship using class private final field , constructor parameter (more or less did) or using private field , setter.

public interface {  void methoda(); }  public class aimpl implements {   @override   void methoda() { /* .... */ } }  public class b { // b not implement a!   private final a; // use interface not implementation   public b(final a) { this.a = a; }   public void methodb() { /* ... */ } } 

or

public class b { // b not implement a!   private a; // use interface not implementation , not final   /* setter , getter */ } 

it not matter of whether bad or not share reference of parent/external object, depends on design requires , have model application accordingly. in first example b implements a's interface, b acts while in latter b not implement a's interface , depends on a: there's subtle important difference.