java - Working with multiple Classes. Program won't launch -

i've been working on rather large program, , thought time split classes. 1 .java file gui code, , 1 .java file mechanics behind functions gui presents. here's issue, i've created instance of each class inside each other, , program refuses launch, i'm doing wrong. in rpg class have following line of code:

public mechanics mechanics = new mechanics(); 

and mechanics class, have code:

public rpg rpg = new rpg(); 

the reason why i'm doing try this: lot of variables in rpg class, , want able call them rpg , manipulate them, send them rpg here code used test function (from mechanics class):

class mechanics{ public rpg rpg = new rpg();   public mechanics(){   }   public void helloworld(){     system.out.println("hello world!");     system.out.println("health before:"+rpg.health);     rpg.health = rpg.health - 5;     system.out.println("health after:"+rpg.health);   }  } 

yes, health public int in rpg class.

and in rpg class, code using test mechanics class:

mechanics.helloworld(); 

here's problem: code compiles, when try run it, error:

 @ mechanics.<init>(mechanics.java:15)  @ rpg.<init>(rpg.java:127) 

here's question. doing right? whats wrong code that's making program not want run?

added: have tried called other classes private well, , program compile, , still refuses launch, , feeds me same error

line 15 of mechanics:

public rpg rpg = new rpg(); 

line 127 of rpg:

public mechanics mechanics = new mechanics(); 

line 15 of mechanics might more like:

public rpg rpg = new rpg(this); // must in constructor or non static method 

in rpg:

public mechanics mechanics; 

in constructor:

this.mechanics = mechanics;