Slide 1 of 40.Lecture A

מבוא למדעי המחשב

Slide 2 of 40.Lecture A

Lesson A - Introduction

Unit A1 – About This Course

Slide 3 of 40.Lecture A

נעם ניסןמרצה:•:(218נין רוס, חדר ב )2:00-3:00 ג’ שעת קבלה

מיכאל אוקון, מעאוויה עקש,ר שרוניי נמתרגלים:•

www.cs.huji.ac.il/~intro2cs אתר הקורס:•

ספר הקורס:•

Java software solutions / Lewis & Loftus

מבוא למדעי המחשב

Slide 4 of 40.Lecture A

. Javaתכנות נכון בשפת תוכן הקורס:

מטרות הקורס:

רמות הפשטה מרובות: •ממשק ומימוש

הנדסת תוכנה•:מעבדת תכנות, מבני קורסים

נתונים

מערכות חישוב ותוכנה•:מיתוג, מסדי נתונים, קורסים

מערכות הפעלה

אלגוריתמים• :אלגוריתמים, חישוביות קורסים

מבני נתונים•:מבני נתונים, מסדי נתונים קורסים

שפה ומשמעות•:מתמטיקה, לוגיקה, קורסים

חישוביות, שפות תכנות, מהדרים

Slide 5 of 40.Lecture A

נושאי הקורס

תכנות מונחה עצמים:•שימוש באובייקטיםכתיבת אובייקטיםירושהממשקים

שיטות תכנות:•רקורסיהמבני נתונים דינמייםתבניותממשק משתמש

אלמנטים בסיסיים:•מבנה התוכנית וניסוחהמשתנים וביטויםפקודותבחירותלולאותמערכיםחריגות

תיאוריה:•ניתוח זמן ריצהמה ניתן לחישוב

Slide 6 of 40.Lecture A

דרישות הקורס

תרגיל תכנות כל שבוע )לפעמים כל שבועיים(. •ן ברירהיהרבה עבודה. א. מומלץ לדון עם חבריםאסור!!!!! להעתיק:דיון = דיבורים בעל פה -- אין הכנסה או הוצאה של חומר הבחנה

כתוב או מודפס.

מבחן • 50/50ציון סופי: •

רגיל נמוך ביותרתציון תרגילים יחושב בהתעלמות מציון

Slide 7 of 40.Lecture A

תלמידים ללא רקע תכנותי

הקורס מיועד לכם )וגם למי שיש לו רקע(•חודש ראשון יהיה קשה מאוד )קצת משעמם למי שיש רקע(•עד סוף הקורס צפוי "יישור קו" של כולם•מנגנוני עזרה:•

שעור עזר במהלך חודש ראשון פלדמן א20:00-18:00שלישי •

ייעוץ במעבדותhttp://www.cs.huji.ac.il/~intro2cs/toranot.htmlרשימת תורנות •

שעות קבלהקבוצת דיון

Slide 8 of 40.Lecture A

Lesson A - Introduction

Unit A2 - Introduction to Hardware

Slide 9 of 40.Lecture A

Our abstraction of a computer

ScreenScreen KeyboardKeyboard

CPUCPU

Java Program

Java Program

MemoryMemory

DataData

Slide 10 of 40.Lecture A

Computer Organization Overview

KeyboardKeyboardScreenScreen DiskDisk ModemModem

Bus

Operating System

Compiler

Our Program

…

Data

SoftwareSoftware

Random Access MemoryRandom Access Memory

CPUCPU

Slide 11 of 40.Lecture A

Binary Representations

• Digital Computers only deal with 0 and 1• We don’t care (mostly) • Anything can be represented by sequences of 0 and 1:

Integers: • 13 = “0000 1101”, 14 = “0000 1110” …

Characters:• ‘A’ = “0010 0001”, ‘B’ = “0010 0010” ...

• The number of bits determines the number of items that can be represented 2 bits give 4 combinations (00, 01, 10, 11) 8 bits (a byte) give 256 combinations 32 bits (a word) give more than 4,000,000,000 combinations

Slide 12 of 40.Lecture A

An Example PC Specification

• 1.1 GHz Pentium IV Processor• 256 MB RAM• 20 GB Hard Disk• 17” Display with 1280 x 1024 resolution• 56 KB Modem

Slide 13 of 40.Lecture A

More about Hardware

• Much more to learn• Not the topic of this course• Other courses deal with computer hardware

Digital Systems course Computer Architecture course Digital Communications course Advanced courses

• In this course, we stick with our abstraction

Slide 14 of 40.Lecture A

Lesson A - Introduction

Unit A3 – Introduction to Software

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Problems and Algorithms

• We need to solve a computational problem “Simulate an Boeing 767 airplane” “Convert a weight in pounds to Kg”

• An algorithm specifies how to solve it, e.g.:1. Read weight-in-pounds

2. Calculate weight-in-Kg = weight-in-pounds * 0.455

3. Print weight-in-Kg

• Computers must be given exact instructions• A computer program is a computer-executable description

of an algorithm

Slide 16 of 40.Lecture A

Machine languages

• Each processor has its own machine language• An assembly language is a human-readable form of the

machine language

load R7, valueload R7, value

jgt label3jgt label3

add R7, bonusadd R7, bonus

0100 0111 1101 0011 ...0100 0111 1101 0011 ...

0101 1011 0110 0111 ...0101 1011 0110 0111 ...

0110 0111 1010 1100 ...0110 0111 1010 1100 ...

Slide 17 of 40.Lecture A

• Humans prefer programming in a high level language• A compiler can translate to machine language• A Interpreter can execute high-level code

High Level Languages

load R7, valueload R7, value

jgt label3jgt label3

add R7, bonusadd R7, bonus

If )value < 0( If )value < 0(

value = value + bonusvalue = value + bonus

CompilationCompilation

Slide 18 of 40.Lecture A

Operating Systems

• Provides hardware-dependant services in a hardware-independent way

• Used by application programs• OS services to users

Files Printing Communication Running programs

• OS services to application programs All of the above Memory Management User Interface Processes

Slide 19 of 40.Lecture A

Lesson A - Introduction

Unit A4 – First Java Program

Slide 20 of 40.Lecture A

The Java Programming Language

• Invented 1995 by James Gosling at Sun Microsystems.• Based on previous languages: C, C++, Objective-C, …• Intended to be a safe programming language for the

Internet• Common choice for first programming language

Object oriented Encourages good programming habits Very popular commercially Simpler and more elegant than C++, but similar to it Cool

Slide 21 of 40.Lecture A

Hello World Program

// My First Program!!public class HelloWorld { public static void main(String[] args){ System.out.println(“Hello World!”); }}

Slide 22 of 40.Lecture A

Java Program Elements

• Words Keywords Identifiers

• Constants Numbers Strings

• Symbols ( ) [ ] { } , . ; + - * /

• Comments

Slide 23 of 40.Lecture A

Java Elements

// My First Program!!public class HelloWorld { public static void main(String[] args){ System.out.println(“Hello World!”); }}

Comment

Identifier Symbols

KeywordsString Constant

Slide 24 of 40.Lecture A

Java Program Structure

• A program is composed of a collection of classes• Each class contains a collection of methods• Each method is composed of a sequence of instructions

(commands, statements)

Slide 25 of 40.Lecture A

Java Program Structure

// My First Program!!public class HelloWorld { public static void main(String[] args){ System.out.println(“Hello World!”); }}

Class

Method

Instruction

Slide 26 of 40.Lecture A

Lesson A - IntroductionUnit A5 – Running Your Program

Slide 27 of 40.Lecture A

Running a Java Program

• Use an editor to enter (type) the program Save to a file named HelloWorld.java

• Use the compiler to translate the program into bytecode javac HelloWorld.java This produces a file named HelloWorld.class

• Run the program using the Interpreter java HelloWorld

Slide 28 of 40.Lecture A

Java Compilation

CompilerCompilerXxx.javaXxx.java Xxx.classXxx.class

InterpreterInterpreter

Output

Slide 29 of 40.Lecture A

Entering a Java Program into an Editor

Slide 30 of 40.Lecture A

Running a Java Program

Slide 31 of 40.Lecture A

Integrated Development Environments (IDE)

• Include a combination of: Editor Compiler Debugger Project Management

• Some Commercial IDEs Sun Forte IBM Visual Age Borland Jbuilder …

Slide 32 of 40.Lecture A

Forte – Screen Capture

Slide 33 of 40.Lecture A

Debugging

• You will make many errors! • Most of your time will be spent finding them and correcting

them -- debugging.• There are several types of errors:

Syntax errors • detected at compilation time

Run-time errors • the program runs and crashes

Logical errors • the program does something other than what you want it to do• It does exactly what you told it to do

• The earlier an error is caught, the easier it is to correct

Slide 34 of 40.Lecture A

Lesson 1 - IntroductionUnit A6 – Introduction to Objects

Slide 35 of 40.Lecture A

Large Programs

• Commercial software may require millions of lines of code• Humans can only handle about 7 things together• To construct large programs:

break the program into components then break each component, etc.

• When you use a component you only use its abstraction.• When you construct a component you forget about the

rest of the program.

Slide 36 of 40.Lecture A

Interfaces

• The interface of a software component is an exact definition of what it can do

• It does not address how it does what it does• When you use a component you only consider its interface• A good component will have a clear, narrow interface

Slide 37 of 40.Lecture A

Objects

• Objects are the basic components in Java• An object has an interface and an internal state.• The interface encapsulates (hides) the internal operation• The interface specifies the services the object provides

Object A that uses Object BObject A that uses Object B Object BObject B

Slide 38 of 40.Lecture A

A Turtle Object

Slide 39 of 40.Lecture A

A Turtle Object

• A Turtle object represents a turtle that walks on the screen with a pen on its tail

• Turtle object interface: moveForward(distance) moveRight(degrees) moveLeft(degrees) tailUp() tailDown()

• Turtle object internal state Location on screen Direction facing Tail is up or down

Slide 40 of 40.Lecture A

Using a Turtle

public class TurtleDrawing { public static void main(String[] args){ Turtle leonardo = new Turtle(); leonardo.tailDown(); leonardo.moveForward(100); leonardo.turnRight(60); leonardo.moveForward(100); }}