Transcript Kickstart Intro to Java

Kickstart Intro to Java
Part I
COMP346/5461 - Operating Systems
Revision 1.6
February 9, 2004
May 9, 2002
Serguei A. Mokhov,
[email protected]
1
Topics
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Me, Myself, and I
Why Java 1.2.*?
Setting Up the Environment
Buzz about Java
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Java vs. C++
Basic Java Syntax
Compiling and Running Java Programs
Example(s)
• Next Tutorial
• References
May 9, 2002
Serguei A. Mokhov,
[email protected]
2
Me, Myself, and I
• Name: Serguei Mokhov, for simplicity just
Serguei, no “Sir”s please!!! :-)
• E-mail: mokhov@cs - maybe the best way to
reach me. Questions are welcome (but please
allow some time to reply - I’m only one and
you’re so many :-) ).
• My Course web page for COMP346/546:
http://www.cs.concordia.ca/~mokhov/comp346/
May 9, 2002
Serguei A. Mokhov,
[email protected]
3
Setting Up the Environment
• Please, refer to the separate set of slides for Java
version and setting up environment.
May 9, 2002
Serguei A. Mokhov,
[email protected]
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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 aren’t
buzzwords, it’s just an incomplete summary
of the features of the language.
May 9, 2002
Serguei A. Mokhov,
[email protected]
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Java vs. C/C++
• Java’s 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.
May 9, 2002
Serguei A. Mokhov,
[email protected]
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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.
May 9, 2002
Serguei A. Mokhov,
[email protected]
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Java vs. C/C++ (3)
• Java DOESN’T 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…
May 9, 2002
Serguei A. Mokhov,
[email protected]
8
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.
May 9, 2002
Serguei A. Mokhov,
[email protected]
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Java Program Structure (2)
• main()
– Declaration:
public 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 we’ll see in a
moment.
– Note, unlike in C/C++, there’s no return value that you
have to explicitly pass back using the return <int>;
statement. Use System.exit(<int>); instead.
May 9, 2002
Serguei A. Mokhov,
[email protected]
10
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! It’s me again!”);
}
}
May 9, 2002
Serguei A. Mokhov,
[email protected]
11
Examples (2)
• Command Line Arguments
ShowArguments.java
public class ShowArguments
{
public static void main(String argv[])
{
A public property
of an array object
for(int i = 0; i < argv.length; i++)
System.out.println(“Arg[“ + i + ”]: ” + argv[i]);
}
}
May 9, 2002
Simple string concatenation with “+”
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[email protected]
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Compiling and Running a Java
Application
• Command line compiler: javac
javac HelloWorld.java
• To run the compiled code you have to
invoke JVM to interpret it:
java HelloWorld
(Note: no extension this time, just the name
of the main class!)
May 9, 2002
Serguei A. Mokhov,
[email protected]
13
On-line Tutorial
• Sun’s Tutorial on Java:
http://java.sun.com/docs/books/tutorial/
• Material for the course:
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Getting Started
Learning the Java Language
Essential Java Classes, especially Thread and Object
Collections
• For your own pleasure and enjoyment:
– Everything else :-)
May 9, 2002
Serguei A. Mokhov,
[email protected]
14
Next Tutorial
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Arrays
Exception Handling
Basics of Inheritance in Java
Threads and Scheduling
More Examples
Whatever I forgot to mention above and
your questions.
May 9, 2002
Serguei A. Mokhov,
[email protected]
15
Links and References
• Official Java site: http://java.sun.com
• Java in a Nutshell, Second Edition by David
Flanagan, (C) 1997 O’Reily & Associates, Inc.
ISBN: 1-56592-262-X
• Past semester’s stuff from Paul and Tony on Dr.
Aiman Hanna’s web site:
http://www.aimanhanna.com/concordia/comp346/
• Manual pages for ssh, vim, [x]emacs, pico
May 9, 2002
Serguei A. Mokhov,
[email protected]
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