General Java Discussion

Between Session 3 (last time) and this session, I intended to have a very open, very flexible discussion about a variety of topics using the the Western Town code as a starting point. 

Today's starting point:

• WesternTown.java
• Human.java
• Book.java

The materials below SHOULD loosely correspond to the topics we discuss, although the order below will NOT necessarily correlate with the order discussed in class.  If you see a topic below that was not covered in class or in your textbook and you are still confused, please see me.

Java data

• There are 8 primitive data types. 
  • 4 are whole numbers (byte, short, int, long)
  • 2 are decimal numbers (float, double)
  • char
  • boolean
• The types in bold are the types we will most often use
• Every other data types that you use in Java are all referential data type. These data types come from one of several sources.
  • First, they may be code that is standard Java.  String is an example of this.  There are literally thousands of these classes.  Just to get a little look at how you might find out about them, we spent a few minutes looking at the Java API for v1.6 (what is in the labs).
  • Second, they may be code that others have written but are not standard Java.  When you download code that the author wrote or that I wrote these fall into this category
  • Third, it may be code that you write.  (the difference between this and #2 is minor but does exist.  More on this as the semester evolves)

Vocabulary and discussion points when we introduce defining objects (referential data type)

• Class header
• Instance variables
• Access modifiers
• Method headers and types
  • Return type
  • parameters
  • Access methods
  • Mutator methods
• Printing in Java
• Naming conventions
  • Class and file names
  • Instance variable names
  • Method names

• instance variables
  • tend to be first
  • "always" private access
  • order of the three pieces needed to "declare" these MATTERS
  • Although IVs get a default value at declaration time, this is considered VERY bad form to depend on it.
  • Although it is possible to initialize IV at declaration time, this is normally bad style
• constructors
  • "the role of the constructor is to initialize the instance variables" (see above)
  • ALWAYS public access (why?)
  • Tends to be second.  That puts it near the IVs
  • Can be told apart from methods because it has the same name as the class and has no return type (see discussion on methods below)
• methods
  • have four parts to their signature
    • access
    • return type
    • name
    • parameters
  • can have either private or public access depending on purpose

While I have proposed an order for these three things, these are really a style issue

Creating a "main" class

• But a class on its own is nearly worthless.
• The purpose of a class is to serve as a template for creating individual objects, or instances, of the class.

WesternTown sweatyPost = new WesternTown();