cosc 1p02 intro. to computer science 1.1 cosc 1p02 week 1 lecture slides "if a man does his...

COSC 1P02

Intro. to Computer Science 1.1

Cosc 1P02

Week 1 Lecture slides

"If a man does his best, what else is there?”

General George S. Patton (1885-1945)

COSC 1P02

Intro. to Computer Science 1.2

COSC 1P02 Audience

planning to major in COSC Staff

instructors: Dave Hughes (J312) & Dave Bockus (J324) mentor: Baoling Bork (J304) tutorial leader: lab demonstrators:

Lectures (AS216), labs (J301), tutorials (AS203) Web

COSC: http://www.cosc.brocku.ca/ COSC 1P02: http://www.cosc.brocku.ca/offerings/cosc1p02/

Email Dave Hughes: hughesd@brocku.ca Dave Bockus: bockusd@brocku.ca

Succeeding in COSC 1P02 labs/assignments

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Intro. to Computer Science 1.3

Course Content and Procedures All course documents available through Computer Science Website:

www.cosc.brocku.ca/Offerings/1P02/ COSC home page: www.cosc.brocku.ca

Outline Instructional labs

lab participation Assignment preparation

Help Desk (J304) submission (outside J332) return (J333) plagiarism

Exams/tests lab vs written

course procedures plagiarism

students with computers Software: JCreator or Dr. Java Libraries

BasicIO TurtleGraphics Media

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Intro. to Computer Science 1.4

Class Room

Ground Rules Lecture conduct Cell Phones Laptops

Contact information: Email messages only accepted from a Brock server. Dave Bockus

Open Door Policy (J324, Day Section) E-mail bockusd@brocku.ca MSN bockusd@hotmail.com

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Intro. to Computer Science 1.5

Computer ScienceWhat is it? study of computer hardware and algorithms and data

structures and how they fit into information systems. computer

programmable machine. processes data into information.

Algorithm well-defined sequence of steps to produce an

outcome programming language

JavaHardwareData In Info Out

AlgorithmSoftware

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Intro. to Computer Science 1.6

Hardware Components

processor (CPU) control unit (CU)

controls system follows instructions

arithmetic logic unit (ALU) performs operations (e.g. +, -, =, <)

main memory (RAM) volatile

input devices transformation keyboard, scanner, sensor

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Intro. to Computer Science 1.8

Hardware Components.

output devices transformation monitor, printer, actuator

auxiliary storage hard disk, floppy disk, CD-ROM, DVD, Data Keys

communications Networks ( wired, broadband) modem, cable modem

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Intro. to Computer Science 1.9

Data Representation

switches—bi-stable devices binary system

positional (like decimal) bit byte megabyte (MB)

memory organization storage cell address store(write)/fetch(read)

Address, where the info is located.

Data, what is stored.

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Intro. to Computer Science 1.10

All information is represented in binary code numbers characters

coding scheme sound, images

Digitization Important: bytes of data only differ in how they are

interpreted. The same byte can be viewed as: Simple representation

Numbers (integers and floats) Characters (abc…)

Part of Complex Objects Pictures, sounds, video

Program Machine Code which instructs the hardware.

Its all in the interpretation

Data Representation (2)

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Intro. to Computer Science 1.11

Instruction Processing

machine language Opcode (operation code) Operand (source data to be used in the operation)

CPU registers

Special Registers IAR, IR bus

machine (fetch/decode/execute) cycle fetch decode execute system clock

1 megahertz (Mhz) = 1,000,000 cycles/second

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Intro. to Computer Science 1.17

Machine LanguageAssembly Language First generation

One-to-one correspondence with hardware function Binary representation Operator (opcode) Operands

Developed into Assembly by allowing mnemonics to represent the actual machine instructions.

made life easier for the programmers.

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Intro. to Computer Science 1.18

High-level Language

Closer to problem domain One-to-many translation

Code much easier to write and understand Made writing large programs much easier.

Required: Compiler

Takes source program Converts to object program {something the

machine can understand} Libraries

linker Compile time vs Link time vs Execution time

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Software Software

computer program instructions for machine execution

Compiler Translation of a high level language into machine

language. Program preparation

edit editor

compile compiler syntax errors

link add in resources (code) from library

execute execution (logic) errors (bugs)

Development environment (IDE, e.g. DrJava, JCreator)

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Intro. to Computer Science 1.20

Computer Programming

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Intro. to Computer Science 1.21

Java

Gosling (1990-92) Originally for consumer electronics

embedded systems Platform independence Object-oriented

programming as modeling Java as a better C++

Execution of Java programs platform independence

machine language? Java bytecode

Java interpreter

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Intro. to Computer Science 1.22

Java Programming Concepts

library (package) e.g. Media collection of useful classes imported to be used

class e.g. Turtle definition of a kind of entity (object) defines operations (methods) entities can perform

object one entity from a class (a turtle) created using new

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Intro. to Computer Science 1.23

variable e.g. yertle name that refers to an object or value

method e.g. forward an operation that can be performed by an object

statement a line of Java code

method call statement request for an object to perform a method object.methodName(parameters)

e.g. yertle.forward(40)

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Intro. to Computer Science 1.24

Turtle Graphics Simple graphics facility

Derived from Logo TurtleDisplayer

a class in the BasicIO library canvas of 300 by 300 drawing units

Turtle a class in the Media library draws on a canvas

Drawing a square create displayer create turtle put turtle on canvas put pen down draw line turn corner repeat

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Intro. to Computer Science 1.28

Turtle Displayer This is equivalent to a piece of paper which the turtle will

draw on. Create the Displayer Put the turtle on the Displayer This also implies we can have more then 1 turtle on

the same displayer. Displayer and Turtle are resources provided by libraries.

We do not make the paper we use. We let someone else do this for us.

Code is linked in to our program If you want a piece of paper you have to have a

access to it. Same for a pencil

Import statement allows us access to these libraries.

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Intro. to Computer Science 1.29

A Java Program

Draw a square Framework

a program is a class code for a class is stored in a file a class is part of a package establish (import) environment (libraries) define names (variables) being used constructor is a method that is executed when an

object is created contains actions (statements) to be performed

main method creates an instance of the DrawSquare class to begin execution

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Intro. to Computer Science 1.30

package Example_2_1;

import BasicIO.*;import Media.*;import static java.lang.Math.*;

public class DrawSquare { private TurtleDisplayer display; // display to draw on private Turtle yertle; // turtle to do drawing public DrawSquare ( ) { display = new TurtleDisplayer(); yertle = new Turtle(); display.placeTurtle(yertle); yertle.penDown(); yertle.forward(40); yertle.right(PI/2); yertle.forward(40); yertle.right(PI/2); yertle.forward(40); yertle.right(PI/2); yertle.forward(40); yertle.right(PI/2); yertle.penUp(); display.close(); }; // constructor public static void main ( String[] args ) { new DrawSquare(); }; }

Import, make libraries visible.

Declare the variable display & yertle.

Create the Objects we need to use, Drawing Surface -> display and the Turtle -> yertle.

Use yertle by calling methods.

Put the Turtle on the Surface.

Basic Program Components

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Draw Square Program Flow

package Example_2_1;

import BasicIO.*;import Media.*;import static java.lang.Math.*;

/** This class is a program to draw a square using Turtle Graphics. * * @author D. Hughes * * @version 1.0 (July 2007) * * new concepts: java program structure, declarations, constructor, object creation, * object assignment, method calls, turtle displayer, turtle graphics */

public class DrawSquare { private TurtleDisplayer display; // display to draw on private Turtle yertle; // turtle to do drawing public DrawSquare ( ) {/** The constructor. */

display = new TurtleDisplayer(); yertle = new Turtle(); display.placeTurtle(yertle); yertle.penDown(); yertle.forward(40); yertle.right(PI/2); yertle.forward(40); yertle.right(PI/2); yertle.forward(40); yertle.right(PI/2); yertle.forward(40); yertle.right(PI/2); yertle.penUp(); display.close(); }; // constructor public static void main ( String[] args ) { new DrawSquare(); }; } Program starts by

creating a new Square Object

Variables declared in the class body are called instance variables. Each new Object will have its own instance variables.

display

yertle

yertle

Yertle is instructed to put its pen down and draw a square.

Wait until the display close button is pressed, then exit

Constructor finishes and program ends

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Intro. to Computer Science 1.34

The end