Head First Java Chapter 3 Essentials

• There are two types of variables: primitive primary data types and references.
• A variable declaration must have a type and a name.
• The primitive primary data type variable value is represented by the bytes of the value.
• The value of the reference variable represents the access method of the object located on the heap.
• A reference variable is like a remote control, and using the dot operator on a reference variable can access its methods or instance variables as if pressing a button on the remote control.
• A reference variable that does not refer to any object has a null value.
• An array must be an object, regardless of whether the element it lives is of the primary primary data type, and there is no array of primary primary data type, only arrays loaded with primary primary data type.