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Welcome to CISC101
Elements of Computing Science I
ILC213, Tuesdays and Thursdays 9:00am, May 2 to
June 10
Prof. Alan McLeod ([email protected])
Goodwin Hall Rm.550
TA – Lili Barbour ([email protected])
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CISC101 - Prof. McLeod
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Course Web Site
• Note that all my lecture slides are (or will be!) on
the web site:
http://www.cs.queensu.ca/home/cisc101spring
• Site also has syllabus, lab exercises, and will
have links to assignments when they have been
written.
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Today
• Introduction to course
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Introduce TA?
Introduce students!
Overview of Syllabus
Grading
Textbook
• What’s an algorithm?
• What’s a program?
• What is “Java” and why use it?
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Introductions All Round!
• Can you log in? Go to course web site:
www.cs.queensu.ca/home/cisc101spring
• (Later – try logging into WebCT site).
• Who wants to use a computer at home?
• Who will use a textbook?
• What’s your computer background?
• What do you want to get out of this course?
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Lab/Tutorial
• Lab is Jeffrey Hall 155 (basement)
• When? Up to you!
– Tuesday afternoon?
– Wednesday?
– Thursday afternoon?
• No lab this week before our Thursday lecture.
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What is the Course About?
• How to create algorithms.
• How to build a program from an algorithm.
• How to use programming elements common to
modern computer languages.
• Provide a basic foundation for further
development of your programming skills.
• Having fun, whenever possible!
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Course Topics - Programming
• Java basics
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Variable declaration
Expressions
Conditionals
Loops
Input/Output (“I/O”)
Methods
Arrays
…
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Course Topics - Generic
• How to express a sequence of steps as an
algorithm.
• How to code an algorithm so that a computer can
carry out the steps.
• Learn good coding style and how to create
documentation.
• Learn debugging techniques.
• Writing efficient code.
• Learn some useful algorithms.
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Grading
• The scheme:
25% assignments
25% midterm
50% final exam
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What Else?
• Keep an eye on the web site - especially the main
page. New content is frequently added, and the
main page contains announcements.
• Make sure I have your preferred E-mail address.
• Any questions?
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What is an Algorithm?
• An experiment:
– Suppose we need
to tell someone who
has never washed
socks before (like
my 18yr old son…)
how to roll them up.
– We know they have
two hands and
understand English.
– No graphics
allowed!
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Socks - Cont.
• Observations
– Not always easy to provide precise instructions!
– Parts of the instructions are repetitious - it is nice to
have some mechanism to allow us to repeat some
“blocks” of instructions.
– Suppose we did such a good job with these instructions
that we were hired to write similar instructions for other
clothing items - it would be nice to re-use some parts of
these instructions…
– Anything else?
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So, What is an Algorithm?
• We just developed one!
• A set of precise, unambiguous instructions
that lead to the solution of a problem.
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What is a Program?
• The sock instructions were in English.
• If we have to communicate an algorithm
to a computer, we’ll need to use a
language that is more easily interpreted
than English.
• A computer “language” is a very small
subset of the human communication
language.
• That’s because computers are very
stupid!!
• They only do exactly what you tell them.
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Computer Architecture (PC)
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Acronyms!!
• CPU - “Central Processing Unit”
– The heart of the computer.
– Consists of millions of transistors on a single
chip.
– Next slide shows the physical layout of a
pentium chip.
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CPU - Cont.
• The latest: Dual Core – two processors on one
chip!
• As hardware, they are characterized by their clock
speed, which controls the number of operations
per second that they can carry out.
• The first PC contained an 8080 chip, introduced in
1979 that had a clock speed of 2 MHz or
(2,000,000 cycles per second).
• Now Pentium IV’s operate at at least 2 GHz!
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CPU - Cont.
• Responsible for:
– Locating and carrying out program instructions
from RAM.
– Carrying out arithmetic operations on data
stored temporarily in a few “registers”.
– Moving data between RAM and other storage
devices (except for those devices that can use
“DMA” - Direct Memory Access).
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CPU - Cont.
• A CPU can only carry out machine language
instructions.
• All high level program instructions must be
reduced to machine code before the CPU can do
anything with them.
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RAM and ROM
• “Random Access Memory”
– Volatile memory - when the power goes off,
bye-bye go the bits!
– Ultimately, numbers are stored in binary format
(1 or 0) - more on this topic later!
– RAM holds data and program instructions.
• “Read Only Memory”
– Not volatile.
– Contains code and (BIOS) data used to start
(“boot”) the computer.
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Other Components
• Disk storage:
– Data stored on magnetic or optical media.
– Not volatile! (Hopefully!)
– Disk read/write operations are much slower
than operations carried out in RAM by the CPU.
– Program code is first loaded from the disk to
RAM and then executed.
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Other Components
• Data ports
– Serial (RS232), Parallel, USB, PS2, etc.
– Providing input/output for the user via the
keyboard, mouse, monitor, sound card,
microphone, printer, scanner, joystick, webcam
(etc. - you get the idea!)
• Modem, Network card and/or Wireless Adapter
– Provide a means of connecting to other
computers.
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What is a Program? - Cont.
• A program is an algorithm expressed using a
language that can be understood (interpreted) by
a computer.
• Many such languages exist:
– Some are closest to how the computer “thinks” (in
binary!), such as machine language:
582134
6A2204
6B2311
502132
(means “X = Y + Z - W”)
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Computer Languages
• Each hexadecimal “byte” (8 bits, where a bit is
either 1 or 0) of this language is translated into
binary code that can be used at the
microprocessor level.
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Computer Languages - Cont.
• Machine language requires very little
interpretation by the computer, but has very little
resemblance to anything that a human can
understand.
• Next comes Assembler language:
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Assembler Language Example
BEEPSEG
BEEP
BEEP
BEEPSEG
SEGMENT
ASSUME
PROC
MOV
MOV
INT
INT
ENDP
ENDS
END
BYTE PUBLIC
CS:BEEPSEG
‘PROG’
DL,7
AH,2
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• Any guess as to what this does?
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Computer Languages - Cont.
• Each assembly language command would need
to be interpreted to several machine language
commands.
• The next generation of computer languages went
up one more level, getting closer to something
readable - for example: Fortran, Cobol and Lisp.
• These languages led to an explosion of over 200
languages being developed in the 60’s and 70’s,
such as Basic, Pascal, C, Ada and Smalltalk.
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Java
• Java was developed about 15 years ago!
• Java is an Object-Oriented language that is very
high level - meaning that it is close to being easily
readable.
• This means that one command in Java could
require many, many machine language
instructions to execute.
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A Very Brief History of Java
• The language was first developed by
James Gosling at Sun Microsystems
in 1991.
– He was designing a language, called
“Oak”, for the “Green Project”.
– The Green Project envisaged the
centralized control of many processorbased devices in the home.
– “Oak” was designed to be a robust,
efficient language with maximum
portability to different processors.
– The Green Project flopped…
– But “Oak” was to soon become “Java”!
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Java History, Cont.
• As soon as Internet use started to blossom in the
early 90’s, a need arose to have web pages do
more than just display static text and graphics.
• Web pages needed to be “programmable”, so that
they could do more - especially so that they could
interact with the viewer of the page.
• The problem is that web pages are viewed on a
wide variety of platforms, from Mac’s to Unix to
IBM-PC’s.
• So any page-embedded language would need to
run on all these platforms.
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Java History, Cont.
• In 1994, Sun demonstrated the use of Java in
small bundles of code embedded in a web page called “applets”.
• Netscape browsers started supporting applets in
1995, starting Java’s rise to fame.
• Sun programmers continued to develop a code
base for the language, demonstrating that Java
could be used for more than just applets, and that
full-blown applications could be written in this
high-level language.
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How Java Works
• The Java language standard (the “syntax”) is
identical for all platforms.
• A compiler (“JDK”, or “Java Development Kit”)
which is designed to run on your development
platform, compiles your source code to a “byte
code” file (“*.class” file extension).
• The byte code file is platform-independent, and is
the thing you attach to your web page as an
applet.
• Every browser written for every platform and OS,
can have an embedded code processor called a
JVM, or “Java Virtual Machine”, built-in.
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How Java Works, Cont.
• The JVM takes the byte code and executes it by
generating the machine code that will be
recognized by the platform that is running the
browser.
Remote Server (Unix)
Local Client (Wintel PC)
HTML File
Netscape Browser
Internet
Applet
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Applet
Byte code files
CISC101 - Prof. McLeod
JVM
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How Java Works, Cont.
• Of course it did not take long before people took
the JVM out of the browser so that they could run
stand-alone Java applications.
• The concept of “write once, run anywhere” is very
appealing!
• And, Sun distributes the JDK’s for free (see
java.sun.com), making development on many
platforms inexpensive.
• Java now has 2.5 million application programmers
worldwide. No other language has ever grown
this quickly!
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How Java Works, Cont.
• So, Java can be used either to create applets for
use in web pages or for stand-alone applications.
• Most “Integrated Development Environments” or
“IDE”’s will support the development of either kind
of program.
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How Java Works, Cont.
• All IDE’s (or “Integrated Development
Environments”) must use the appropriate JDK
from Sun in the background.
• Two components of the JDK are the programs
“javac.exe” and “java.exe”.
• javac.exe is the byte code compiler, and java.exe
is the JVM which executes the byte code file.
• “Compilation” is the process of converting the
*.java file to a *.class file (the byte code file). This
is done by calling javac.exe in the background,
and supplying that program with all the required
command line parameters.
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How Java Works, Cont.
• The java.exe program:
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accepts the byte code file,
links in any required libraries,
creates executable code in memory
converts it to machine language
and sends it to the CPU.
• The java.exe program must know the right
machine language commands only for the type of
CPU it is designed for!
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Source
text
Text
Editor
successful
Eclipse or
BlueJ
Bytecode
binary
Compiler
Executable
binary
not
successful
Linker
Errors
javac.exe
Loader
Library
binary
Input
Data
java.exe
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CISC101 - Prof. McLeod
Output
Data
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How Java Works, Cont.
• So, Java can be used either to create applets for
use in web pages or for stand-alone applications.
• Most “Integrated Development Environments” or
“IDE”’s will support the development of either kind
of program.
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Why Java for CISC101?
• The choice of the language is fairly arbitrary.
• Java is:
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Multiplatform,
Modern, Object - Oriented,
Supported by a Large User Base,
Not Vendor-Specific,
Fundamentally Sound.
• Other good languages: C, C++, C#, Delphi
(pascal), Visual Basic, Turing, etc.
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Why Java? - Cont.
• “IDE” - Integrated Development Environments
(like those from Microsoft) make it easier to build
GUI Interfaces.
• “GUI” - Graphical User Interface.
• We don’t want to get hung up on all the GUI
elements necessary to build a “Windows”
program.
• Learn structural programming first.
• Need a simple development environment, not one
that is oriented only towards Windows platform
development.
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Why Java? - Cont.
• Use Java to demonstrate your knowledge of
programming.
• In particular, we will use “Java II” which is also
referred to as “JDK, version 1.5” or “Java 5.0”.
• Two development tools are recommended: BlueJ
and Eclipse.
• Available here and in in Jeff Lab.
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Development Environments - Cont.
• You can use any environment you wish (JBuilder,
Sun JDK, BlueJ, Eclipse, etc.) - but we cannot be
expected to support them all.
• The programs you write and submit could be run
on any platform in any environment.
• Let “us” have a look at three possible
development environments:
– DOS command line (java.sun.com)
– BlueJ (www.bluej.org)
– Eclipse (www.eclipse.org)
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Three Environments
• Which to use?
• Use DOS if you like pain…
• BlueJ is simple but not realistic.
• Eclipse is a “real” tool – this is the one I’m going
to use in class most often.
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For Example - HelloWorld.java
• In Notepad:
// The "HelloWorld" class.
public class HelloWorld {
public static void main (String[] args) {
System.out.println("Hello World!");
} // end main method
} // end HelloWorld class
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For Example - HelloWorld.class
• In Notepad:
Êþº¾
HelloWorld
java/lang/Object
main
([Ljava/lang/String;)V
Code
LineNumberTable
Ljava/io/PrintStream;
out
java/lang/System
Hello World!
(Ljava/lang/String;)V
println
java/io/PrintStream
<init>
()V
HelloWorld.java SourceFile !
%
²
¶ ±
!
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CISC101 - Prof. McLeod
*·
±
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Next Time
• Down to the business of learning Java:
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Primitive types
Variable declaration
Operators
Expressions
Mixed type expressions
Casting
• A program “template”
• Screen output
• Screen input
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