8. java constructor.txt

constructor:
-special method of a class 
-called when the object is created 
-used to initialize the object of the class i.e. initialize the variables of the object

rules of writing the constructor:
-can have the access modifier 
-cannot be static 
-cannot be final 
-cannot be abstract 
-cannot be synchronized 
-cannot have any return type
-name should be same as the name of the class 
-can have parameters
-Can be overloaded (multiple constructors in the same class with different parameters)

types of constructors in java:
1. default:
-automatically by default there provided by java if we dont define any constructor in java 
-has no parameters 
-since it has no parameters, it initializes the instance variables(non static) to the default variables 

2. no arguments constructor:
-defined by the programmer 
-no arguments are present
-instance is initialized by the default variables values 
-since its the custom defined, we can code any custom logic in it 

3. parameterized constructor:
-defined by the programmer 
-accepts some parameters
-initializes the instance variables with the parameters injected into the constructor

4. private constructor:
-having the access modifier as private 
-since the access modifier is private, the constructor cannot be accessed outside of the class, and therefore, no object 
can be created outside of the class, and therefore, this prevents the creation of the object from outside of the class 
-since the access modifier is private, we can use the constructor inside its own class only and therefore can create the 
object there only and nowhere else
-used in singleton design pattern where a single object creation is permitted

constructor overloading:
-having multiple constructors overloaded into the same class 
-since the overloadeding is done by differencing in the parameter list, the parameter list for all the constructors 
should be different 
-this is done for creating generality in the application code, depending on the inputs the user provide to the application 

constructor chaining:
-when one constructor calls the other constructor
-in the class, for accesing any method, we use the this.methodName notation and therefore should use the this.constructorName 
notation for calling the constructor but actually, we use only this keyword 
-e.g., this(10,20) //calling the constructor which accepts two integers in its parameters list 

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