Kickstart Intro to Java Part I

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Kickstart Intro to JavaPart I

• COMP346/5461 - Operating Systems
• Revision 1.6
• February 9, 2004

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Topics

• Me, Myself, and I
• Why Java 1.2.?
• Setting Up the Environment
• Buzz about Java
• Java vs. C
• Basic Java Syntax
• Compiling and Running Java Programs
• Example(s)
• Next Tutorial
• References

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Me, Myself, and I

• Name Serguei Mokhov, for simplicity just
  Serguei, no Sirs please!!! -)
• E-mail mokhov_at_cs - maybe the best way to reach
  me. Questions are welcome (but please allow some
  time to reply - Im only one and youre so many
  -) ).
• My Course web page for COMP346/546
  http//www.cs.concordia.ca/mokhov/comp346/

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Setting Up the Environment

• Please, refer to the separate set of slides for
  Java version and setting up environment.

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Why is Java sooo co0OL???

• Dear Serguei, you promised an Intro to Java!!
• Here it goes Java is a quite simple, OO,
  distributed, interpreted, robust and secure,
  platform and architecture independent,
  multithreaded and dynamic language.
• A bunch of buzzwords? No, they arent buzzwords,
  its just an incomplete summary of the features
  of the language.

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Java vs. C/C

• Javas syntax is very similar to that of C/C
  thus, it is quite easy to learn for C/C
  programmers.
• However, there are some conceptual differences
  behind this syntactical similarity, which you
  should pay close attention to.

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Java vs. C/C (2)

• Java
• is pure OO language unlike C/C.
• has everything as an object with and exception of
  few primitive data types (int, float, etc.).
• uses two-byte (16 bit) Unicode characters.
• has well defined and sometimes mandatory to use
  the Exception Handling Mechanism (will be covered
  later).
• has automatic garbage collection.

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Java vs. C/C (3)

• Java DOESNT have
• Multiple inheritance (well, it somewhat does
  through interfaces and, but this is not a true
  inheritance).
• Templates. Vast majority of objects inherit from
  the Object class or its descendants (implicitly
  or explicitly), so any object can be cast to the
  Object class.
• Pointers, only references. All objects
  manipulated by reference by default in Java, not
  like in C. So, there is no in the syntax for
  function parameters.
• Operator overloading
• Some others

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Java Program Structure

• Since Java is a pure OO language even the main()
  function has to be defined in a class.
• An instance of the class, which defines main(),
  will be the main thread when run.
• There should be only one public class with main
  in a file and the file name must be the same
  (including capitalization and spelling) as the
  main class name plus the .java extension.
• In general one (any) public class per file. It
  is possible to have more than one class defined
  within one .java file, but only one of them
  should be public and the file name should
  correspond to that, public, class name.
• When a java program compiled with no errors with
  javac, a JVM object code is produced and stored
  in .class files. One file per class.

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Java Program Structure (2)

• main()
• Declarationpublic static void main(String
  argv)
• The argv is a list of arguments passed via
  command line, just like in C/C.
• There is no argc in Java for a reason well see
  in a moment.
• Note, unlike in C/C, theres no return value
  that you have to explicitly pass back using the
  return ltintgt statement. Use System.exit(ltintgt)
  instead.

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Examples

• Immortal Hello World Application

Note, a java file must be named as
HelloWorld.java public class HelloWorld
public static void main(String argv)
System.out.println(Hello dear World! Its me
again!)
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Examples (2)

• Command Line Arguments

ShowArguments.java public class ShowArguments
public static void main(String argv)
for(int i 0 i lt argv.length i)
System.out.println(Arg i
argvi)
A public property of an array object
Simple string concatenation with
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Compiling and Running a Java Application

• Command line compiler javacjavac
  HelloWorld.java
• To run the compiled code you have to invoke JVM
  to interpret itjava HelloWorld(Note no
  extension this time, just the name of the main
  class!)

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On-line Tutorial

• Suns Tutorial on Javahttp//java.sun.com/docs/b
  ooks/tutorial/
• Material for the course
• Getting Started
• Learning the Java Language
• Essential Java Classes, especially Thread and
  Object
• Collections
• For your own pleasure and enjoyment
• Everything else -)

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Next Tutorial

• Arrays
• Exception Handling
• Basics of Inheritance in Java
• Threads and Scheduling
• More Examples
• Whatever I forgot to mention above and your
  questions.

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Links and References

• Official Java site http//java.sun.com
• Java in a Nutshell, Second Edition by David
  Flanagan, (C) 1997 OReily Associates, Inc.
  ISBN 1-56592-262-X
• Past semesters stuff from Paul and Tony on Dr.
  Aiman Hannas web sitehttp//www.aimanhanna.com/
  concordia/comp346/
• Manual pages for ssh, vim, xemacs, pico