When we create a setter method in java , how does java know to which variable we want to set the given value from the setter ? read discription please

Question

In my given Image you can see that I have created a Class named employee with one variable with no assigned value.Also I have given getter and setter methods. Now the queston i have is that , in the Setter method i.e (setsalary) , I am taking a integer value into the variable s and then assigning it to the salary variable. Now when I create an object of that particular class ( as you can see in the image), how does the program knows that the given value of salary has to be assigned to the salary of the object i.e (John.salary) , I mean i have only written salary=s; and nothing else. How does the program setts the value exactly to the object ?

Answer 1

how does the program knows that the given value of salary has to be assigned to the salary of the object i.e (John.salary) , I mean i have only written salary=s; and nothing else

The missing ingredient is the this keyword:

Within an instance method or a constructor, this is a reference to the current object — the object whose method or constructor is being called. You can refer to any member of the current object from within an instance method or a constructor by using this.

What isn't written there is that the this keyword is OPTIONAL, thus this line:

salary=s;

and this line are equivalent:

this.salary=s;

So it knows which instance (John in this case) to use because there is actually an invisible "this" in front of "salary" telling it to assign to the CURRENT OBJECT.