The Java Programming Language

1
The Java Programming Language

• Stand Alone Programs
• Internet Applets
• Structured with methods
• Object Orientated Programming
• Abstract Data Types
• Use Beyond the PC

2
Java Programs Applets

• Programs are compiled into classes
• Programs are run by a Java Virtual Machine (JVM)
  (i.e. interpreter)
• MS Visual J lets us compile into an .exe

• Applets are compiled into classes
• Applets are run by a JVM- usually a web browser
• Applets are launched by an HTML web page.

3
Java Methods

• Methods are like BASIC subroutines
• Methods that return a value are similar to BASIC
  functions
• When methods return a value they have a type
  (i.e. integer, string, double)
• When methods do not return a value they are
  called void

4
Java Methods Public Private

• Private methods are available only to the classes
  they are created in and the objects they are
  derived from.
• Public methods can be executed from other classes
  and objects.

5
What is a Java class?

• To the JVM, a class is compiled Java code
• In respects to OOP, a class is a model from which
  objects can be created
• To a programmer, a class in a tool for code reuse

6
Java Objects

• Objects are created from classes
• Multiple objects can be created from one class-
  this maximizes code reuse
• Objects can be manipulated easily- similar to
  variables

7
Abstract Data Types

• Classes and objects are considered abstract data
  types
• Classes and objects are ways of better
  representing the world we live in.
• An object can be thought of as the things around
  us.
• A class can be thought of as a collection or
  category of objects

8
Why program in Java?

• According to Sun Microsystems, Javas future lies
  not only with the Internet but with all household
  devices which will eventually become intelligent
  or computer automated.
• Imagine the near future where all of our
  computerized possessions can recognize each other
  as Java objects.