Main Concepts from Chapter 4:

• The scope of a variable:

  All variables are members of the block of code in which they are defined. This allows for two scope designations:

  1. Local variables are defined inside the block of code specifying a method body, and, therefore belong to that method. They can only be used within the body of the method where they are declared.
  2. Instance variables are defined outside of the body of any method, but inside the body of a class. As such, instance variables belong to a class, i.e., they are members of a class. They can be used anywhere inside of the class definition. Because they are members of a class, they also exist in every object of that class (i.e., if the class name is Dog, then every Dog object will contain any instance variables defined in the Dog class). All public members of a class (both instance variables and methods) can be used by methods that are not members of the class.

  
  

• Encapsulation

  Instance variables are typically encapsulated by declaring them to have private access. A class member that is declared to be private can only be accessed by other class members. Public methods provide the interface (i.e., user access) to private instance variables.

  
  

• Parameters and Return Values

  A return value is used to send information (a single value) from the callee method to the caller method. Parameters facilitate the sending of information (one value per parameter) from the caller method to the callee method. A parameter is just like a local variable (belonging to the callee method) except that it gets its initial value from the caller method. The actual parameter establishes the initial value of the formal parameter.