In java or any other language how method or constructor knows about those things which are declared in the class .

Today if 100 people are using java or any programming in this world but i am sure that 30 people in those 100 people does not know the reason behind " In java or any other language how method or constructor knows about those things which are declared in the class . " 


if you are not clear than watch this  ...

----------
{
     int a ;
    method_1 ( )
    {
       // question :- now how this method knows about " int a "
    }
}
----------