I have a very basic java theory question. Why the Employee class calls its self recursively in the following example?
class Employee { Employee emp = new Employee(); } public class Manager extends Employee { public static void main(String[] args){ Manager mgr = new Manager(); } } Look at what the code is doing:
When you create a new Manager object, the Employee part of that Manager object is also going to be initialized (because Manager extends Employee).
When the Employee part is initialized, its emp member variable is going to be initialized. It will be initialized with a new Employee object. But that object also has an emp member variable, which will be initialized with a new Employee object. And that object also has an emp member variable, which will be initialized with a new Employee object. And that object also has an emp member variable, which will be initialized with a new Employee object. And that object also has an emp member variable, which will be initialized with a new Employee object. And that object also has an emp member variable, which will be initialized with a new Employee object. And that object also has an emp member variable, which will be initialized with a new Employee object. ... etc. until the stack overflows.
Manager extends Employee, so the Employee part of the Manager object will also be initialized, leading to the recursive loop.
Manager object, you create a new Employee object, when you create a new Employee object, its emp member variable is going to be initialized. It will be initialized with a new Employee object. But that object also has an emp member variable, which will be initialized with a new Employee object...Employee part of the Manager object is going to be initialized.
Skip the commented object creation, every time you create an Employee which happens when you create Manager because it inherits it, it enters an internal loop.
class Employee { //Employee emp = new Employee(); } 
class Employee { Employee emp = new Employee(); } What this means is that each Employee contains an instance of another Employee. As such, when your Employee is constructed, it also has to create the Employee it contains. However, by the same logic, that Employee must also have its own child Employee that must be constructed, and so on.
Employeecreate, is it because you thought you have to create it, in order to have inheritance hierarchy or it's by choice, a composition, you want each Employee to have a reference to another employee? Maybe we can help you further.