Lesson 1 - Introduction

1
???? ????? ?????
2
Lesson A - Introduction

• Unit A1 About This Course

3
???? ????? ?????

• ???? ??? ????
• ??? ???? ? 200-300 (???? ???, ??? 218)
• ??????? ??? ?????, ????? ?????, ??????? ???
• ??? ????? www.cs.huji.ac.il/intro2cs
• ??? ?????
• Java software solutions / Lewis Loftus

4
???? ????? ????? ???? ???? Java.
????? ?????

• ???? ????? ?????? ???? ??????
• ????? ?????
• ?????? ????? ?????, ???? ??????
• ?????? ????? ??????
• ?????? ?????, ???? ??????, ?????? ?????

• ??????????
• ?????? ??????????, ????????
• ???? ??????
• ?????? ???? ??????, ???? ??????
• ??? ???????
• ?????? ???????, ??????, ????????, ???? ?????,
  ??????

5
????? ?????

• ????? ????? ?????
• ????? ??????????
• ????? ?????????
• ?????
• ??????
• ????? ?????
• ???????
• ???? ?????? ???????
• ??????
• ???? ?????

• ??????? ???????
• ???? ??????? ???????
• ?????? ???????
• ??????
• ??????
• ??????
• ??????
• ??????
• ???????
• ????? ??? ????
• ?? ???? ??????

6
?????? ?????

• ????? ????? ?? ???? (?????? ?? ???????).
• ???? ?????. ??? ?????.
• ????? ???? ?? ?????
• ????!!!!! ??????
• ????? ???? ??????? ??? ?? -- ??? ????? ??
  ????? ?? ???? ???? ?? ?????.
• ????
• ???? ???? 50/50
• ???? ??????? ????? ???????? ????? ????? ???? ?????

7
??????? ??? ??? ??????

• ????? ????? ??? (??? ??? ??? ?? ???)
• ???? ????? ???? ??? ???? (??? ????? ??? ??? ???)
• ?? ??? ????? ???? "????? ??" ?? ????
• ??????? ????
• ???? ??? ????? ???? ?????
• ????? 2000-1800 ????? ?
• ????? ???????
• ????? ?????? http//www.cs.huji.ac.il/intro2cs/to
  ranot.html
• ???? ????
• ????? ????

8
Lesson A - Introduction

• Unit A2 - Introduction to Hardware

9
Our abstraction of a computer
Screen
Keyboard
Java Program
Data
CPU
Memory
10
Computer Organization Overview
Modem
Keyboard
Screen
Disk
Bus
Software
Operating System
Compiler
Our Program

CPU
Data
Random Access Memory
11
Binary Representations

• Digital Computers only deal with 0 and 1
• We dont 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

12
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

13
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

14
Lesson A - Introduction

• Unit A3 Introduction to Software

15
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

16
Machine languages

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

load R7, value jgt label3 add R7, bonus
0100 0111 1101 0011 ... 0101 1011 0110 0111
... 0110 0111 1010 1100 ...
17
High Level Languages

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

load R7, value jgt label3 add R7, bonus
If (value lt 0) value value bonus
Compilation
18
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

19
Lesson A - Introduction

• Unit A4 First Java Program

20
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

21
Hello World Program
// My First Program!! public class HelloWorld
public static void main(String args)
System.out.println(Hello World!)
22
Java Program Elements

• Words
• Keywords
• Identifiers
• Constants
• Numbers
• Strings
• Symbols
• ( ) , . - /
• Comments

23
Java Elements
Comment
Symbols
Identifier
// My First Program!! public class HelloWorld
public static void main(String args)
System.out.println(Hello World!)
Keywords
String Constant
24
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)

25
Java Program Structure
Class
Method
// My First Program!! public class HelloWorld
public static void main(String args)
System.out.println(Hello World!)
Instruction
26
Lesson A - Introduction

• Unit A5 Running Your Program

27
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

28
Java Compilation
Xxx.java
Xxx.class
Compiler
Interpreter
Output
29
Entering a Java Program into an Editor
30
Running a Java Program
31
Integrated Development Environments (IDE)

• Include a combination of
• Editor
• Compiler
• Debugger
• Project Management
• Some Commercial IDEs
• Sun Forte
• IBM Visual Age
• Borland Jbuilder

32
Forte Screen Capture
33
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

34
Lesson 1 - Introduction

• Unit A6 Introduction to Objects

35
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.

36
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

37
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 B
Object B
38
A Turtle Object
39
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

40
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)