A Caffeinated Primer on Java

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A Caffeinated Primer on Java

• By Garabed (Garo) Yeriazarian

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Object - Orientation

• Purely object-oriented
• Everything is an object (well, sort of)
• Single Inheritance only
• Multi Interface Inheritance
• Always Polymorphic (C virtual keyword)
• Standardized Exceptions
• Easy.asPie()

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Whats so special about Java (the language, not
the beverage)?

• C style syntax and constructs (but simpler)
• Write Once Run Anywhere (Sun gets a nickel every
  time someone says this)
• Virtual Machine provides security and garbage
  collection among other things
• Full-featured API (less work for you!!!)
• Built-in documentation mechanism (javadoc)
• Packages (C namespaces) for organization

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However Java pitfalls (come on, you know there
had to be some)

• Java byte-code is interpreted by the VM (can be
  slow depending on the system)
• Multi-platform is nice, but deployment is not
  always easy (without buying tools)
• Jokes about caffeine, coffee, etc get really old
  really fast
• Requires Virtual Machine (10MB download) on the
  client machine for deployment

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Tools You Want / Need to Use Java

• Borland JBuilder 8 Personal (free)
• You need to register and get a free key too
• Contains the J2SE SDK 1.4.1
• Dont forget to download the docs separately
  (56MB)
• IDE for easy Java development
• Windows (50MB), Solaris (60MB), and Linux (70MB)
• Latest and greatest J2SE (Java 2 Standard
  Edition) SDK from http//java.sun.com (free)
  (38MB)
• Get the documentation too (necessity!!!) (32MB)
• These are command-line tools only, no IDE
• Makes you love high speed internet access, eh?
  ,-)

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Howdy World!
/////////////////////////////////////////////// //
HowdyWorld.java Obligatory Intro
program //////////////////////////////////////////
///// public class HowdyWorld public static
void main(String args)
System.out.println(HOWDY WORLD!!!)
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Compiling and Executing

• Create the HowdyWorld.java file (case matters)
• Make sure your path is set to include the Java
  bin folder where java.exe and javac.exe reside
• javac HowdyWorld.java (case matters)
• This will generate the HowdyWorld.class file
• java HowdyWorld (case matters)
• Itll grind a bit, then you get HOWDY WORLD!!!

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The Basics of Java Console Apps

• A Java program can be made up of one or more
  .java files. Each .java file contains one class
  (not required, but highly recommended)
• To be able to execute a Java application, the
  entry point class must contain the main method
  public static void main(String args)
• Static means that this method is executed
  independent of any instances of the class (same
  meaning as in C)

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Lets See Something A Little More Complicated
(Im getting bored)

• Fine, check out the Wordifier.java file from the
  samples on the presentation page
• This program will read in a line of text, parse
  it into words, and spit out the results along
  with a word count and average word length
• The program is heavily commented, so you
  shouldnt have too much trouble following it
• This program will illustrate reading in from the
  console, writing to the console, use of several
  primitive types, use of strings, and use of
  classes
• ltDemo of Wordifiergt

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((int)(11)) Types of Variables

• Primitive Types are like standard C types, they
  are automatically allocated and freed by the
  Virtual Machine
• Objects are instances of classes, they are NOT
  automatically allocated by the Virtual Machine,
  you must explicitly instantiate them using the
  new operator

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Java Primitive (oogah) Types
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Classes and Objects

• Data types are called Classes, instances of a
  class are called Objects
• In Java, every object is a reference
• In C, you could have objects that were
  allocated / deallocated on the stack
  automatically by the compiler.
• So what? Well, you have to be careful with the
  operator, the next slide will explain why

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Snafu about Objects

• Say you have the following code snippetPoint a,
  ba new Point(1,1)b aSystem.out.println(
  Point A a)System.out.println(Point B
  b)a.x 3System.out.println(Point A
  a)System.out.println(Point B b)
• Output (not quite what you expect)Point A
  (1,1)Point B (1,1)Point A (3,1)Point B
  (3,1)

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Stringin Yall Along

• Strings get preferential treatment in Java
• For examples, see all the sample programs
• A String is immutable
• To modify a string, you must make a new one or
  look into the StringBuffer class
• Every class has a toString() method to convert an
  object into its string representation
• String concatenation with operator
  (automatically calls the toString() method of
  non-string objects
• Remember, a string is still an object
  reference!!!
• To copy a string strNew new String(strOld)

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Everybody Loves Arraymond

• Cmon, you know you want to know all about
  arrays!
• Java treats arrays as objects
• Array dimensions are defined ONLY at runtime (not
  compile time like C)
• int intArray new int10int int2DArray
  new int1020
• The dimensions dont have to be constants
• intArray.length 10int2DArray.length
  10int2DArray0.length 20
• All arrays are, like C, 0-based

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Important Thing about Classes!!!

• One interesting thing about Java is that all
  classes automatically inherit from
  java.lang.Object
• Uh, so what?
• Well, glad you asked ,-) in Java, all methods
  are (in C terms) virtual (you could also say
  polymorphic)
• So, you could set up an array of Objects, then
  assign any object to any element of that array
• Java also maintains runtime type information
  (RTTI in C)
• Java also provides an operator instanceof that
  you can use to test the type-compatibility of an
  objectif (MyObject instanceof String) // do
  stuff

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Sheeyooot, dats purdy cool!

• I guess you wanna test it out, eh? Heh, I knew
  you would, so I made a nice little test program
  called the UberArray (UberArray.java and
  TestUberArray.java)
• This example serves multiple purposes
• To show you how to use multiple classes in your
  programs
• To show you how to do Arrays
• To show an example of Java polymorphism
• Say you wanted to make (oh, I dont know) a queue
  (hint hint, nudge nudge), then you could design
  it to be able to hold any arbitrary type (object
  type, not primitive type unless you use the class
  wrappers)

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Using Multiple .class Files Together

• Java makes it super-easy to reuse existing code.
• You dont need access to the source files, just
  the compiled .class file
• Drop it into the same folder as the main program
  you are writing, then use the class as you would
  any other class
• No need for specific import statements (see
  UberArrray example for an example)
• Example You have a class called MyDataClass
• Compile to get MyDataClass.class
• In DoData.java, say you want to use MyDataClass,
  you just declare a variable of type MyDataClass
  and the VM will grab the right .class file, load
  it and use it

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Try Not to Lose Interface

• Java classes are single-inheritance only!!!
• However, you can use interfaces (C pure
  abstract base classes) to use a cleaner type of
  multiple inheritance and allow objects to be used
  in a more general manner
• Example (Informable.java)public interface
  Informable public String getInformation()
• This can be used to develop a standard plug-in
  system for your application or to further
  separate interface from implementation

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Thats It for the Primer

• So, by now, you should have a basic understanding
  of Java (hopefully, unless I did a bad job) ,-)
• Hopefully, yall will try out all the samples I
  put together on your own to get a feel for how
  Java works
• Most likely all this talk about Java fired up a
  craving for some Frappuchinos from Starbucks

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Ok, So Where Do I Go From Here?

• Check out the Sun Java Tutorialshttp//java.sun.
  com/docs/books/tutorial/
• Buy some books on Java (check the links on the
  presentation web page)
• Stuff I didnt cover (out of scope for this
  primer)
• GUIs, Events, Threads, Packages, File I/O,
  Networking
• Cmon, yall are smart people, read up on this
  stuff in books
• Or, you can email me on WebCT (Garabed
  Yeriazarian) or real email GaroY_at_aol.com
• Although the best thing to do would be to post
  your questions / comments in the Java Forum for
  everyone to see