java - composite inheritance: how to assign a final field at sub-class constructor which depends on 'this' value (backward reference)? -

i use composite classes group functionalities.
but, class (with composite a1), got inherited b (with composite b1), , behavior existent @ a1 going adapted @ b1, final a1 must b1 instance work.

obs.: have ways make sure composite instantiation happens (only composite partner).

unable assign b1 object a1 final field:

class finalfieldtestfails{     class a1{       a1(a a){}     }      class a{       protected final a1 a1;       a(){         this.a1 = new a1(this);       }        a(a1 a1){         this.a1 = a1;       }     }      class b1 extends a1{       b1(b b){         super(b);       }     }      class b extends a{         //b(){ super.a1=new b1(this); } //fail: cant change final value         //b(){super(new b1(this));} //fail: cant use 'this' or 'super'     } } 

ps.: answer shall not involve reflection security tricks if possible.

b(){ super.a1=new b1(this); } //fail: cant change final value

you can not assign values assigned final variables, can instantiate within constructor not following.

b(){super(new b1(this));} //fail: cant use 'this' or 'super'

you can use once instance created only. since there inheritance tree, not instantiated, compiler complains,

cannot reference before supertype constructor has been called