Transcript Unit 5 (PowerPoint) - Huji cse Moodle 2014/15

Introduction to Computer Science
Unit 5
 Basic
Elements of Java
 A Look at Hardware and
Software
What this Course is Not
 This
is not a course on Java, even
though we spend time learning this
language
 It’s
a course introducing Computer
Science, which also means introducing
programming (principles are better
understood when they are concrete)
 Java
is a means to what we want to
accomplish, not an end in itself
5- 2
Course Mission Statement
“To give the student the tools to
develop correct, efficient, wellstructured, and stylish programs,
and to build a foundation for further
studies in Computer Science.”
-An Introduction to Computer Science with Java
Kamin, Mickunas, and Reingold
5- 3
Why We Like Java
 Java
is Object Oriented to the core
 Java
is, in certain key ways,
simpler than other Object Oriented
languages (like C++)
 Java
is well-suited to the Internet
 Java
is cross-platform
 Java’s
popularity creates its own
momentum
5- 4
A Simple Program
A
Java application:
class Hello {
public static void main (String[ ] args) {
// Say hello.
System.out.println(“Hello!”);
}
}
5- 5
A Simple Program
A
Java application:
class Hello {
public static void main (String[ ] args) {
// Say hello.
System.out.println("Hello!");
}
}
5- 6
The Way You Might Type It
(sometimes I’ll do it this way, too)
A
Java application:
import intro.utils.*;
import java.io.*;
public class Hello {
public static void main (String[ ] args) {
// Say hello.
System.out.println("Hello!");
}
}
5- 7
Take it Apart
import some classes
import intro.utils.*;
import java.io.*;
public class Hello {
class heading
method heading
public static void main (String[ ] args) {
//
}
}
Say hello. comment
System.out.println("Hello!");
print out “Hello!”
5- 8
Java Cares About File Names
 Type
the program into a file named
Hello.java (case matters)
 Java
demands that the class name
(here, “Hello”) must also be the base
name of the file into which you put it
 The
extension of the file must be .java
 Hence,
 Each
Hello.java
Class requires a separate file
5- 9
Steps to Nirvana
 Type
the program into a file named
Hello.java (case matters; really)
 Compile
it
 Execute
it
 The
program displays the message
Hello!
on the screen
5- 10
Compilation

Many high-level languages, like C, Pascal, or
C++, must be compiled before they are run

Compilation means translation into the native
language of the computer

Each computer (Wintel, Macintosh, Sun Sparc,
etc.) has its own native language, so compiling
the same program for each computer would
create something different

The statement “x = 3 + 2;” would be translated
into a sequence of low-level operations
5- 11
Compilation
C, Pascal, or C++ program
Source code
Compilation
1001110110101101
1101110001011010
Machine code
for some
specific
machine
5- 12
Interpretation
 Other
languages, like Lisp and SmallTalk,
are interpreted
 They
don’t get translated directly into
machine language
 Instead,
they are given to an interpreter,
which is a program that performs each
operation in the program on the computer
statement “x = 3 + 2;” would cause
some sequence of operations to be
carried out
 The
5- 13
Interpretation
Lisp or SmallTalk program
Source code
Read by an
Interpreter
Lisp or SmallTalk
Interpreter for a
Specific Machine
Machine instructions
for some specific
machine
5- 14
Some Differences

Compilation and Interpretation differ in many
ways

When machine code is generated/activated


At compile time with compilation

At run-time with interpretation
The kind of machine code that is
generated / activated


Compilation can do optimizations
The flexibility of development

Interpreters are more flexible because you don’t have
to recompile when you make changes to a program
5- 15
Compilation can do optimizations
 Let’s
say you had the following lines of
code:
y = 7;
w = 4;
x = y + w;
A
reasonable compiler will realize what
is happening and replace the last line
with machine code that puts 11 into x
 An
interpreter might carry out all the
last line’s sub-operations…
5- 16
Where does Java fit?
 Compilation
is efficient, but machine-
specific
 Interpretation
is flexible, but inefficient
 Java
wanted to be efficient, but also
flexible, and most important:
PLATFORM INDEPENDENT (same
program running on all computers)
 So
Java is compiled and interpreted...
5- 17
Compilation and
Interpretation
A
Java program can basically exist in
one of two states:

Source code (that’s what you are
typing in)
Byte code, a .class file (a translation of
the original code to something closer
to the machine’s language – but
not any real machine’s language)

5- 18
Compilation and Execution
public class Hello {
public static void main...
Source code
(Hello.java file)
Compilation
javac Hello.java
op7 op342 op213 op431
Interpreter
Byte code,
binary file
(Hello.class file)
Execution
java Hello
5- 19
Java Byte Code (.class file)
5- 20
The Java Virtual Machine
 The
Java Virtual Machine is the
interpreter that reads Java byte codes
and carries out real machine operations
 To
get Java running on any kind of
computer, just implement the Java
Virtual Machine
 Presto!
Java is platform independent,
and flexible (interpreted), but still
reasonably efficient (because Java byte
code is close to machine code)
5- 21
Managed Code

This approach in the design of Java is called “managed
code”

Managed code means a program (like the one you write)
must be executed with a runtime environment installed in
the same machine – your program cannot run without it

Other examples of managed code include Visual Basic
and .NET's Common Language Runtime (CLR)

Compiled C or C++ programs are examples of unmanaged
code

“There has been a switch in the last four years toward
using managed code. I'd say maybe half of the stuff that
gets done now is in managed code.”
- Bill Gates, CNet interview, 28.10.2003
5- 22
Another Program
(this one takes input)
 We
want a program that will do the
following:
Please type the temperature (deg C):
20
20 deg C is 68.0 deg F
5- 23
What the Robot World
Lacked
 When
we programmed the robot
world, we had no real variables,
and no real input or output
 In
Java (as in virtually all
programming languages),
variables are essential
 Each
variable has a type
5- 24
Input/Output in Java
import java.util.Scanner;
public class Temperature {
public static void main (String[ ] args) {
int temperature; // The Celsius temperature
Scanner sc = new Scanner(System.in);
System.out.print("Please type the temperature (deg C): ");
temperature = sc.nextInt();
System.out.print(temperature);
System.out.print(" deg C is ");
System.out.print(((9.0 * temperature)/5.0 ) + 32.0);
System.out.println(" deg F");
}
}
5- 25
Helping Perceive Structure
import java.util.Scanner;
public class Temperature {
public static void main (String[ ] args) {
int temperature;
// The Celsius temperature
Scanner sc = new Scanner(System.in);
System.out.print("Please type the temperature (deg C):");
temperature = sc.nextInt();
System.out.print(temperature);
System.out.print(" deg C is ");
System.out.print(((9.0 * temperature)/5.0 ) + 32.0);
System.out.println(" deg F");
}
}
5- 26
WARNING!
 When
you write your programs,
you are to follow the course
guidelines regarding style
 These guidelines are important;
they help groups of programmers
communicate with one another
 Do not assume that what appears
in the slides is written according
to course guidelines. The slides
have different constraints!
5- 27
Variables
public class Temperature {
public static void main (String[ ] args) {
int temperature;
// The Celsius temperature

temperature is a variable

The declaration of the variable
int temperature;
saves a space for a value to be stored later,
but doesn’t store anything there

The assignment to the variable
temperature = sc.nextInt();
actually puts something in the space that was
created by the declaration
5- 28
Variable Declaration
public class Temperature {
public static void main (String[ ] args) {
int temperature;
// The Celsius temperature
temperature
You don’t know what’s in there;
don’t use temperature yet
5- 29
Simple Variable Assignment
temperature = 36;
36
36
temperature
Puts the integer 36 into temperature;
now you can use temperature
5- 30
You Can Combine the Two Steps
class Temperature {
public static void main (String[ ] args) {
int temperature = 36; // The Celsius temperature
36
temperature
5- 31
What the Program Looked Like –
Getting an Integer from the User
import java.util.Scanner;
public class Temperature {
public static void main (String[ ] args) {
int temperature;
// The Celsius temperature
Scanner sc = new Scanner(System.in);
System.out.print("Please type the temperature (deg C):");
temperature = sc.nextInt();
System.out.print(temperature);
System.out.print(" deg C is ");
System.out.print(((9.0 * temperature)/5.0 ) + 32.0);
System.out.println(" deg F");
}
}
5- 32
Variable Assignment –
Getting an Integer from the User
temperature = sc.nextInt();
nextInt()
20
20
sc
20
temperature
Send the sc object a nextInt() message, it returns
an integer (that it gets from the user), which is then
placed in temperature
5- 33
Special “Variables”
that Remain Constant

We can define a variable (a “symbolic
constant”) whose value will never change,
by writing
final int RETIREMENT_AGE = 70;

This carries out assignment at the same
time as declaration (as we can do with any
variable)

Now RETIREMENT_AGE cannot be legally
changed in the program
5- 34
Data Types and Expressions
 Different
kinds of information
 Each kind is a “type”
 Java has many data types
Each type has a name
 Each type has a set of literals
 Each type has a set of operations

 Data
types in Java can be
simple types or object types
5- 35
Different Simple Types in Java
 int
represents integers
 literals like 3 and 132
 operators like + , - , * , /

 double
represents real numbers
 literals like 3.0, 3.14159 and 2.997925e8

 The
integer 3 and the double 3.0 are
represented differently inside the computer
5- 36
More Simple Types in Java
 boolean

Represents true and false
 char

Represents individual
characters that are typed
at the keyboard
5- 37
Expressions
 An
Expression represents a value that can
be used in Java statements

Made out of literals, variables, symbolic
constants, and operations

Every expression also has a type

3 + 4 + temperature

(3.0 / 4.0)* RETIREMENT_AGE (has type double)
(has type int)

Use parentheses to establish the order of
operations

Can also be messages sent to an object or class, if a
value is returned, like sc.nextInt( )
5- 38
Type of an Expression
No matter how simple or
complicated an
expression is, it always
has a Java type, just
like a variable.
5- 39
Where’s the Expression Go?
 An
expression produces a value, which is
then often used in an assignment
statement
 So
typically, the expression is on the right
hand side of the assignment statement:

temperature = 36;

temperature = (x / 7) + y;

temperature = sc.nextInt();
5- 40
The Order of Assignment
 In
general, the computer evaluates the
expression on the right side, and
places that value in the variable on the
left side, replacing the old value. So:
temperature = temperature + 10;
is completely legal; it adds 10 to the
value of temperature
Can also be written:
temperature += 10;
5- 41
Increment/Decrement
 Two
special cases: incrementing
and decrementing
cent++;
is the same as
cent = cent + 1;
cent--;
is the same as
cent = cent - 1;
5- 42
One of Your Own Kind,
Stick to Your Own Kind

Java is very strict about data types and
assignments

Java only puts into a variable a value of the
appropriate type

Expressions having an integer value can go
into an integer variable, etc.

You can’t do this:
int i;
double x = 3.0;
i = 10.3 * x;
5- 43
Special Case
 You
can assign an integer
expression to a double variable

The integer is converted to a double
without loss of information, so it is
done automatically
 You
can do this:
int i = 3;
double x;
x = 10 * i;
5- 44
Converting Values from One
Type to Another

The cast operation lets you explicitly
convert one type to another

You can do this:
int i;
double x = 3.0;
i = (int) (10.3 * x);

The cast (int) takes the expression that
follows it and converts it into an integer by
removing any fractional part; i is assigned
the integer value 30
5- 45
Object Types in Java

The existence of a class in Java lets you have
variables that are of new types, rather than just
simple types

(Java gives us simple types int, double,
boolean, char, etc.)

Every class C defines a set of values called
objects of type C (that is, C is a class name)

Just as you define a new variable to be of type
int, you can define a new variable (object) to
be of type C
5- 46
Defining Objects of Type C
C
u, v, w;
Object type
declares u, v, and w to be objects of type
C (or “variables of type C” or “instances
of type C”)
 This
is similar to writing
int a, b, c;
Simple type
to declare a, b, and c to be variables of
type int
5- 47
One of these things,
Is not like the other
C and D are two different classes,
their objects have different types
 They can’t be assigned to one another
 If u is an object of type C, and:
D t;
// an object of type D
we cannot do either of the following:
u = t;
t = u;
 We also cannot do something like
u = 10;
 If
5- 48
Constructors
 Declaring
a new object just tells the
system the type of the object:
C u;
 To
create the object, we use a
constructor:
u = new C( arguments );
A
constructor is a special method of the
class that creates and initializes the new
object; it has the same name as the class
 It
is the way to create objects
5- 49
Creating Objects and Filling
them with Values
 This
looks a lot like how we created
objects in the robot world
 Yes,
the two statements (declaration and
creation) can be combined:
C u = new C( arguments );
 That’s
all we were doing in the robot
world – combining declaration (declaring
the type of the object) with constructing a
new object
5- 50
They Look the Same
But They are Different
C u
= new C( arguments );
first C and the second C fulfill two
different roles
 The first C tells the type of the object
variable (like int tells the type of a simple
variable)
 The second C is a call to the method C
inside the class C that is the class’
constructor, and creates the object
5- 51
 The
Methods within an Object
u is an object of class C, and class
C has a method called “display”,
then we’ll trigger a method in u by
writing:
u.display( arguments )
 If
 You’ve
already seen the same thing
in the robot world
 We’re
sending the object u a
message “display” with arguments
5- 52
You can also send
messages to Classes
 Unlike
in the robot world, there
are cases when a class is sent
a message, rather than an
object
 Later
we’ll talk about when we
do this kind of thing
5- 53
The String Class
 This
is an important predefined, special
class that we are given as part of the Java
system
 Can be used as follows:
String
t1 = "To be ",
t2 = "or not to be.";
System.out.print(t1 + t2);
prints out: To be or not to be.
 Notice that this is a special case – we are
creating objects without explicitly calling a
constructor
5- 54
The String Class
has some useful Methods
have a method called “length”:
String
t1 = "To be ",
t2 = "or not to be.";
 Strings
 t1.length(
) then is an expression that
returns the integer 6, the number of
characters in the object t1
send the object t1 a message
length( ), and get back the integer 6; we
are asking the object about itself; that’s
common
5- 55
 We
Fun with Strings and +
System.out.print("4"
System.out.print("4"
System.out.print(4 +
System.out.print("4"
System.out.print("4"
System.out.print("4"

+ "5");
+ 5);
5);
+ "005");
+ 005);
* 5);
//prints:
//prints:
//prints:
//prints:
//prints:
//error!
45
45
9
4005
45
An integer concatenated to a string is
automatically converted to a string
5- 56
Statements
 We’ve
seen two Java programs that are
sequences of statements, each statement
either assigning a value to a variable, or an
executable statement that prints output
System.out.print("Please type the temperature (deg C): ");
temperature = sc.nextInt( );
 There
are of course other kinds of
statements, conditionals (if, if/else), and
iterative statements (like for and while
loops)
5- 57
Perceiving Structure, Again
import java.util.Scanner;
public class Temperature {
public static void main (String[ ] args) {
int temperature;
// The Celsius temperature
Scanner sc = new Scanner(System.in);
System.out.print("Please type the temperature (deg C):");
temperature = sc.nextInt();
System.out.print(temperature);
System.out.print(" deg C is ");
System.out.print(((9.0 * temperature)/5.0 ) + 32.0);
System.out.println(" deg F");
}
}
5- 58
Three Ways of Using Methods in your
Programs (we’ll understand why, later)

Every execution starts with some “static”
method main( )

That main( ) method might be in the same class
as your other methods, or it might be in a separate
class (a so-called “driver”)

If main( ) is in the same class as your other
methods, and you use those other methods
directly from main( ) (i.e., without creating an
object), then those other methods must also be
“static”

This is also true of class variables used directly
from main( )
5- 59
Warning!!! Warning!!!
The
following programs are
not good programming
style, they are just
examples of when to use
the keyword “static”!
5- 60
1. Direct (static) use (not real OOP)
class Temperature {
public static int firstTemp;
public static void main (String[ ] args)
int secondTemp;
{
firstTemp = 7;
secondTemp = firstTemp + 9;
printMessage( );
System.out.println("The sum is " + secondTemp);
}
public static void printMessage ( ) {
System.out.println("This is a silly program.");
}
}
5- 61
1. Direct (static) use (not real OOP)
class Temperature {
public static int firstTemp;
public static void main (String[ ] args)
int secondTemp;
{
firstTemp = 7;
secondTemp = firstTemp + 9;
printMessage( );
System.out.println("The sum is " + secondTemp);
}
public static void printMessage ( ) {
System.out.println("This is a silly program.");
}
}
5- 62
A Second Way of Using Methods in
your Programs
if the main( ) method is in the
same class as your other methods, you
can (instead) create an object with a
name, and send messages to the
object
 Even
 Then
those other methods (or
variables) should not be “static”
 This
is similar to what you did in the
robot world…that is, using real objects
in your program
5- 63
2. Use via an Object
class Temperature {
public int firstTemp;
public static void main (String[ ] args)
int secondTemp;
{
Temperature bill = new Temperature( );
bill.firstTemp = 7;
secondTemp = bill.firstTemp + 9;
bill.printMessage( );
System.out.println("The sum is " + secondTemp);
}
public void printMessage ( ) {
System.out.println("This is a really silly program.");
}
}
5- 64
2. Use via an Object
class Temperature {
public int firstTemp;
public static void main (String[ ] args)
int secondTemp;
{
Temperature bill = new Temperature( );
bill.firstTemp = 7;
secondTemp = bill.firstTemp + 9;
bill.printMessage( );
System.out.println("The sum is " + secondTemp);
}
public void printMessage ( ) {
System.out.println("This is a really silly program.");
}
}
5- 65
class StairSweeper extends BasicRobot {
public static void main[String[ ] args] {
StairSweeper larry = new
StairSweeper(2, 1, East, 0);
larry.climbStair( );
larry.pickBeeper( );
larry.climbStair( );
larry.pickBeeper( );
larry.climbStair( );
larry.pickBeeper( );
larry.turnOff( );
}
void turnRight( ) {
turnLeft( );
turnLeft( );
turnLeft( );
}
}
void climbStair( ) {
turnLeft( );
move( );
turnRight( );
move( );
}
8
7
6
5
4
3
2
1
1
2
3
4
5
6
7
8
7
8
Initial Situation
8
7
6
5
4
3
2
1
1
2
3
4
5
6
Final Situation
5- 66
A Third Way of Using Methods in your
Programs

Commonly, the main( ) method will be in a
different class (and file) from your other methods

This driver class might be supplied by the
metargelim, or you might write it yourself

It will create an object with a name, and send
messages to the object

And those object’s methods (or variables) will
not be “static”

This is also similar to what you did in the robot
world…
5- 67
3. Use via an Object in Separate Class
class Driver {
public static void main (String[ ] args)
int secondTemp;
{
Temperature bill = new Temperature( );
bill.firstTemp = 7;
secondTemp = bill.firstTemp + 9;
bill.printMessage( );
System.out.println("The sum is " + secondTemp);
}
}
5- 68
3. Use via an Object in Separate Class
class Temperature {
public int firstTemp;
public void printMessage ( ) {
System.out.println("This is a very silly object.");
}
}
Those are the constraints for using “static” in
your Java programs. We will understand what
“static” really means, later in the course
5- 69
REMINDER –
Importing Class Definitions

Instead of putting all these things together in
one file, we could break them up as follows:
class StairSweeper extends
BasicRobot {
void turnRight( ) {
turnLeft( );
turnLeft( );
turnLeft( );
}
}
void climbStair( ) {
turnLeft( );
move( );
turnRight( );
move( );
}
A file called StairSweeper.java
import StairSweeper;
public static void main[…] {
StairSweeper larry = new
StairSweeper(2, 1, East, 0);
larry.climbStair( );
larry.pickBeeper( );
larry.climbStair( );
larry.pickBeeper( );
larry.climbStair( );
larry.pickBeeper( );
larry.turnOff( );
}
A file called Driver.java
5- 70
What Will NOT Work
class Box {
public int height;
public int width;
public static void main (String[ ] args)
{
System.out.println("The height is " + height);
System.out.println("The width is " + width);
}
The static main method cannot use the
non-static variables “height” and “width”
directly (that is, without creating an object)
5- 71
Debugging a Program
We’re going to walk
through a
debugging of a
sample program
5- 72
Write and Debug a Program
 Compute
the total cost of a coffee order
 ( (Price per pound) x Weight ) + Shipping
 Shipping =
((Shipping Rate per pound) x Weight ) +
Fixed handling fee
 Price per pound and Weight vary
 Shipping Rate per pound and handling
fee are fixed
5- 73
import java.util.Scanner;
class CoffeeOrder {
public static void main (String[ ] args) {
final int
RATE_PER_POUND = 1.25,
FIXED_FEE,
int
priceperPound, weight,
shippingCost, coffeeCost;
Scanner sc = new Scanner(System.in);
System.out.println(“Enter price per pound: );
pricePerPound = sc.nextInt();
System.out.print(“Enter number of pounds: “);
weight = sc.nextInt();
shipingCost = RATE_PER_POUND+weight +FIXED_FEE;
totalPrice = priceperPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
System.out.println(“Shipping cost is “ + shipingCost);
System.out.println(“Total cost is “ totalPrice);
}
}
import java.util.Scanner;
class CoffeeOrder {
public static void main (String[ ] args) {
final int
RATE_PER_POUND = 1.25,
FIXED_FEE,
int
priceperPound, weight,
shippingCost, coffeeCost;
ERROR
Scanner sc = new Scanner(System.in);
System.out.println(“Enter price per pound: );
pricePerPound = sc.nextInt();
ERROR
System.out.print(“Enter number of pounds: “);
weight = sc.nextInt();
shipingCost = RATE_PER_POUND+weight +FIXED_FEE;
totalPrice = priceperPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
System.out.println(“Shipping cost is “ + shipingCost);
System.out.println(“Total cost is “ totalPrice);
}
}
import java.util.Scanner;
class CoffeeOrder {
public static void main (String[ ] args) {
final int
RATE_PER_POUND = 1.25,
FIXED_FEE;
int
priceperPound, weight,
shippingCost, coffeeCost;
Scanner sc = new Scanner(System.in);
System.out.println(“Enter price per pound: “);
pricePerPound = sc.nextInt();
System.out.print(“Enter number of pounds: “);
weight = sc.nextInt();
shipingCost = RATE_PER_POUND+weight +FIXED_FEE;
totalPrice = priceperPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
System.out.println(“Shipping cost is “ + shipingCost);
System.out.println(“Total cost is “ totalPrice);
}
}
import java.util.Scanner;
class CoffeeOrder {
public static void main (String[ ] args) {
final int
RATE_PER_POUND = 1.25,
FIXED_FEE;
int
priceperPound, weight,
shippingCost, coffeeCost;
Scanner sc = new Scanner(System.in);
System.out.println(“Enter price per pound: “);
pricePerPound = sc.nextInt();
System.out.print(“Enter number of pounds: “);
weight = sc.nextInt();
shipingCost = RATE_PER_POUND+weight +FIXED_FEE;
totalPrice = priceperPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
System.out.println(“Shipping cost is “ + shipingCost);
System.out.println(“Total cost is “ totalPrice);
}
}
ERROR
import java.util.Scanner;
class CoffeeOrder {
public static void main (String[ ] args) {
final int
RATE_PER_POUND = 1.25,
FIXED_FEE;
int
priceperPound, weight,
shippingCost, coffeeCost;
Scanner sc = new Scanner(System.in);
System.out.println(“Enter price per pound: “);
pricePerPound = sc.nextInt();
System.out.print(“Enter number of pounds: “);
weight = sc.nextInt();
shipingCost = RATE_PER_POUND+weight +FIXED_FEE;
totalPrice = priceperPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
System.out.println(“Shipping cost is “ + shipingCost);
System.out.println(“Total cost is “ + totalPrice);
}
}
import java.util.Scanner;
class CoffeeOrder {
public static void main (String[ ] args) {
final int
RATE_PER_POUND = 1.25,
ERROR FIXED_FEE;
int
priceperPound, weight,
shippingCost, coffeeCost;
Scanner sc = new Scanner(System.in);
System.out.println(“Enter price per pound: “);
pricePerPound = sc.nextInt();
ERRORSystem.out.print(“Enter number of pounds: “); ERROR
weight = sc.nextInt();
shipingCost = RATE_PER_POUND+weight +FIXED_FEE;
ERRORtotalPrice = priceperPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
ERRORSystem.out.println(“Shipping cost is “ + shipingCost);
System.out.println(“Total cost is “ + totalPrice);
}
ERROR
ERROR
ERROR
}
ERROR ERROR
import java.util.Scanner;
class CoffeeOrder {
public static void main (String[ ] args) {
final double RATE_PER_POUND = 1.25,
FIXED_FEE = 1.95;
int
pricePerPound, weight,
shippingCost, coffeeCost, totalPrice;
Scanner sc = new Scanner(System.in);
System.out.println(“Enter price per pound: “);
pricePerPound = sc.nextInt();
System.out.print(“Enter number of pounds: “);
weight = sc.nextInt();
shippingCost=RATE_PER_POUND+weight +FIXED_FEE;
totalPrice = pricePerPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
System.out.println(“Shipping cost is “ + shippingCost);
System.out.println(“Total cost is “ + totalPrice);
}
}
import java.util.Scanner;
class CoffeeOrder {
public static void main (String[ ] args) {
final double RATE_PER_POUND = 1.25,
FIXED_FEE = 1.95;
int
pricePerPound, weight,
shippingCost, coffeeCost, totalPrice;
Scanner sc = new Scanner(System.in);
System.out.println(“Enter price per pound: “);
pricePerPound = sc.nextInt();
ERRORSystem.out.print(“Enter number of pounds: “);
weight = sc.nextInt();
shippingCost=RATE_PER_POUND+weight +FIXED_FEE;
totalPrice = pricePerPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
System.out.println(“Shipping cost is “ + shippingCost);
System.out.println(“Total cost is “ + totalPrice);
}
ERROR
}
import java.util.Scanner;
class CoffeeOrder {
public static void main (String[ ] args) {
final double RATE_PER_POUND = 1.25,
FIXED_FEE = 1.95;
double
pricePerPound, weight,
shippingCost, coffeeCost, totalPrice;
Scanner sc = new Scanner(System.in);
System.out.println(“Enter price per pound: “);
pricePerPound = sc.nextInt();
System.out.print(“Enter number of pounds: “);
weight = sc.nextInt();
shippingCost=RATE_PER_POUND+weight +FIXED_FEE;
coffeeCost = pricePerPound * weight;
totalPrice = pricePerPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
System.out.println(“Shipping cost is “ + shippingCost);
System.out.println(“Total cost is “ + totalPrice);
}
}
We run the program
Enter price per pound: 8.95
java.lang.NumberFormatException: 8.95
at java.lang.Integer.parseInt(Integer.java)
at java.lang.Integer.<init>(Integer.java)
at …
We’ve got a problem. We tried to read a double
by sending sc the nextInt() message.
5- 83
import java.util.Scanner;
class CoffeeOrder {
public static void main (String[ ] args) {
final double RATE_PER_POUND = 1.25,
FIXED_FEE = 1.95;
double
pricePerPound, weight,
shippingCost, coffeeCost, totalPrice;
Scanner sc = new Scanner(System.in);
System.out.println(“Enter price per pound: “);
pricePerPound = sc.nextDouble();
System.out.print(“Enter number of pounds: “);
weight = sc.nextInt();
shippingCost=RATE_PER_POUND+weight +FIXED_FEE;
coffeeCost = pricePerPound * weight;
totalPrice = pricePerPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
System.out.println(“Shipping cost is “ + shippingCost);
System.out.println(“Total cost is “ + totalPrice);
}
}
We Run the Program Again
Enter price per pound: 8.95
Enter number of pounds: 3
Coffee total is 26.849999999999998
Shipping cost is 6.2
Total cost is 33.05
Great!
Only one problem. The total cost is $0.50 too high.
5- 85
import java.util.Scanner;
class CoffeeOrder {
public static void main (String[ ] args) {
final double RATE_PER_POUND = 1.25,
FIXED_FEE = 1.95;
double
pricePerPound, weight,
shippingCost, coffeeCost, totalPrice;
Scanner sc = new Scanner(System.in);
System.out.println(“Enter price per pound: “);
pricePerPound = sc.nextDouble();
System.out.print(“Enter number of pounds: “);
weight = sc.nextInt();
shippingCost=RATE_PER_POUND*weight +FIXED_FEE;
coffeeCost = pricePerPound * weight;
totalPrice = pricePerPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
System.out.println(“Shipping cost is “ + shippingCost);
System.out.println(“Total cost is “ + totalPrice);
}
}
We Run the Program One Last Time
Enter price per pound: 8.95
Enter number of pounds: 3
Coffee total is 26.849999999999998
Shipping cost is 5.7
Total cost is 32.55
That’s good enough for now.
5- 87
Models
 You
can think about objects in
many different ways
 You
can think about them based on
their responses to actions
 You
can think about it based on
what is “happening inside”
 Even
what is “happening inside”
can be thought of in different ways
5- 88
Models
 How
you look at things can differ
depending on what you want to do
 How
much understanding you need
depends on what you want to do
 You
can often relate to lower levels,
different models, as “black boxes” –
that’s a good thing!
5- 89
When Good Models Go Bad
 Generally,
though, there is a
mismatch between models
 This
becomes especially clear
when something goes
wrong…and the model’s
mismatch becomes confusing…
5- 90
A lock and key
 Put
the key in
 Turn it one way, the door is unlocked
 Turn it the other way, the door is locked
5- 91
A lock and key
A
lock has many different parts
We could think about it based on how
the different parts work together
5- 92
A lock and key
 More
detail than perhaps you need to
know
 There is also the physics description –
springs, forces, friction…
5- 93
And when something goes
wrong…
 What
if the key becomes
damaged?
 Certain
kinds of damage don’t
matter (a key can be shaved
thinner, and it will still work)
 Certain
kinds of damage keep it
from working (a key’s tooth is
broken and it won’t work)
5- 94
Things got even harder with
electricity – Transparent vs.
Opaque Functionality
 At
least there used to be a visible
connection between physical
things and what they did
a
butter churn
a loom
a watch
a lock and key
 The
coming of electrical power
changed that fundamentally
5- 95
The Computer
 The
computer is the supreme example
of opaque function
 Looking
into the box does not help us
to understand what is going on
 The
best way to understand computers
(perhaps the only way) is to understand
the logical layers out of which they are
built
5- 96
The Layers of Computing
Application
Layer
Software
Browser Compiler Games
Utilities
System
Layer
Software
UNIX
Windows
Apple
System
Machine
Layer
Software
Assembly
Languages
Machine
Languages
MicroPrograms
Underlying
hardware
Memory
Screen
CPU
Hard disk
Keyboard
5- 97
Binary Representation
 Everything
in the computer is
represented as numbers
 Everything
 That
includes integers, floating
point numbers, characters,
commands, variables, symbols…
 And,
in fact, it represents them as
the simplest kind of numbers
there are, binary numbers
5- 98
But First, Decimal Numbers
 10
digits, from 0 through 9
 Each column represents a power
of 10: 100, 101, 102, 103, etc. (that
is, 1’s, 10’s, 100’s, 1000’s, etc.)
102
103
100
101
3248
is actually
8 1’s, plus 4 10’s, plus 2 100’s, plus 3 1000’s
But this works just as well if we use a different
number of digits.
5- 99
Binary Numbers
2
digits, from 0 through 1
 Each column represents a power
of 2: 20, 21, 22, 23, etc. (that is, 1’s,
2’s, 4’s, 8’s, etc.)
22
23
20
21
1011
is actually
1 1’s, plus 1 2’s, plus 0 4’s, plus 1 8’s (which
is the same as 11 in the decimal system)
5- 100
Internal Representation
 The
memory in a computer consists
of lots of 0’s and 1’s; each binary
digit is called a “bit”
8
bits is called a “byte”
are organized into “words”,
whose size depends on the specific
computer (usually 32 bits or 64 bits,
that is, 4 bytes or 8 bytes)
 They
5- 101
Computer’s Internal Memory
(Random Access Memory – RAM)
5- 102
Computer’s Internal Memory
(RAM)
32 bits per
word (each
bit holds a
0 or a 1)
5- 103
Computer’s Internal Memory
(RAM)
32 bits per
word (each
bit holds a
0 or a 1)
34 words in
this picture
(there could
be millions)
5- 104
How Much Can be Represented
in one Byte?
 Each column represents
20 , 21 , 22 , 23 , 24 , 25
a power of 2:
, 26 , 27 (that is,
1’s, 2’s, 4’s, 8’s, 16’s, 32’s, 64’s, 128’s)
26
27
24
25
22
23
20
21
10011011
is actually
1 1’s, plus 1 2’s, plus 0 4’s, plus 1 8’s, plus 1 16’s, plus
0 32’s, plus 0 64’s, plus 1 128’s (i.e., 155 decimal).
The smallest number is 0, the largest
number is 11111111, i.e., 255, i.e., 28 - 1
5- 105
Why Are “8 bits” Interesting?
8
bits is sufficient to represent
the numbers from 0 to 255
(enough for a complete table of
English and European letters),
so that’s why it became a
standard grouping of bits
5- 106
More Bytes
With 8 bits, 256 separate numbers
 If you had 10 bits, the biggest number
would be 210-1, or 1023 – you have 1,024
separate numbers
 That’s close to a thousand, and we love
using binary numbers, so we’ll call that a
kilobyte (or KB) – about a thousand bytes
 With 10 bits, I could refer to 1024 separate
places in memory
 A kilobyte of text is 1024 separate
characters

5- 107
More Bytes
 If
you had 20 bits, the biggest number
would be 220-1, or 1048575 – you have
1,048,576 separate numbers
 That’s close to a million, and we love
using binary numbers, so we’ll call that
a megabyte (or MB) – about a million
bytes
 With 20 bits, I could refer to 1048576
separate places in memory, for example
 A megabyte of text is 1048576 separate
characters
5- 108
More Bytes
 If
you had 30 bits, the biggest number
would be 230-1, or 1073741823 – you
have 1,073,741,824 separate numbers
 That’s close to a billion, and we love
using binary numbers, so we’ll call that
a gigabyte (or GB) – about a billion
bytes
 With 30 bits, I could refer to 1073741824
separate places in memory, for example
 A gigabyte of text is 1073741824
separate characters
5- 109
More Bytes
 If
you had 40 bits, the biggest number
would be 240-1, or 1099511627775 – you
have 1,099,511,627,776 separate numbers
 That’s close to a trillion, and we love
using binary numbers, so we’ll call that a
terabyte – about a trillion bytes
 With 40 bits, I could refer to
1099511627776 separate places in
memory, for example
 A terabyte of text is 1099511627776
separate characters
5- 110
How Much Room to Represent
Things Digitally, in Bytes
A character takes 1 byte
 An email message (represented as plain text)
might take up a kilobyte (approximately 40
characters per line x 25 lines)
 A book (represented as plain text) might take
up a megabyte (approximately 70 characters
per line x 45 lines per page x 300 pages)
 100 megabytes could hold 2 volumes of
encyclopedias
 1 Gigabyte could hold the contents of about
10 meters of books on a shelf
 100 Gigabytes could hold the entire library
floor of academic journals

5- 111
How Much Room to Represent
Things Digitally, in Bytes
A
terabyte could hold 1,000 copies of the
Encyclopedia Britannica
 Ten terabytes could hold the printed
collection of the Library of Congress
 A petabyte is approximately 1,000
perabytes or one million gigabytes. 1
petabyte could hold approximately 20
million 4-door filing cabinets full of text
 An exabyte is approximately 1,000
petabytes. “5 exabytes would be equal to
all of the words ever spoken by mankind.”
5- 112
How Much Room to Represent
Things Digitally, in Bytes
A
minute of AVI digital video
(uncompressed) – 200 MB
 One minute of a song in MP3,
sampled at 128kbps (kilobits per
second) – 1 MB
 One minute of a song on a CD –
10 MB
 A typical CD (approximately 45
minutes) – 450 MB
 Maximum on a CD:
783,216,000 bytes (approx. 747 MB)
5- 113
How Do I Represent Music with
0’s and 1’s?
 Analog
sound signal:
5- 114
How Do I Represent Music with
0’s and 1’s?
 Another
analog sound signal:
I can approximate that with discrete sampling, assigning a
number to each sample:
5- 115
How Do I Represent Music with
0’s and 1’s?

The more samples I take, and the more
gradations there are, the greater accuracy I
have of the original analog signal:
5- 116
How Do I Represent Music with
0’s and 1’s?
 Maximum
on a CD (this is the standard):
 44,100 samples per channel per second
 2 bytes per sample means 216
gradations, i.e., 65536 gradations – good
fidelity
 44,100 samples/channel/second x 2
bytes/sample x 2 channels (stereo) x 74
minutes x 60 seconds/minute =
783,216,000 bytes (approx. 747 MB)
5- 117
Standards for Digitization

For this to work, there must be an agreed
upon way of representing characters, music,
graphics, floating point numbers, even
integers, using binary numbers

So government bodies and companies get
together and agree on a CD standard, a DVD
standard, an MP3 standard, a JPEG standard,
a GIF standard, an ASCII standard, etc.

Or they don’t

“The great thing about standards is that there
are so many of them.” (Joke)
5- 118
ASCII Table (uses 8 bits)
5- 119
ASCII Table (not really…)
5- 120
Symbol Font Table
5- 121
Microsoft Windows Codepage :
1255 (Hebrew)
5- 122
Unicode
 To
represent all of the world’s
languages, you need more than 256
places in a table – you need more than
8 bits to represent a character
 The Unicode standard makes use of 32
bits to represent everything in a single
table
 But there are clever ways to keep most
text represented by a single byte
 The Hebrew table in Unicode occupies
the range 0590 to 05FF
5- 123
Hexadecimal Notation
 Sometimes
for convenience sake, 4
binary bits get grouped together and
represented by a symbol between 0 and
9, or between A and F (where A
represents decimal 10 and F represents
decimal 15)
 So:
1001
is written hexadecimal 9
1010 is written hexadecimal A (= decimal 10)
1110 is written hexadecimal E (= decimal 14)
1001 1110 is written hexadecimal 9E (= 158)
5- 124
Hiragana – Range 3040 to 309F
5- 125
Internal Representation
computer word of 32 bits is “just” a
string of 1’s and 0’s:
10011001111011010101010010110110
 It might represent any one of a number
of things:
A
4
characters
An integer
Half of a double (floating point number)
A computer command in machine
language
5- 126
Internal Representation
4 characters
10011001111011010101010010110110

The computer
system itself
must keep track
of what the bits
 An integer
represent --- or
10011001111011010101010010110110
allow a program
to decide at
 Half of a double (floating point number)
runtime.
10011001111011010101010010110110
A computer command in machine language
10011001111011010101010010110110

“machine language”? What’s that?
5- 127
Machine language – Mark I
5- 128
Machine Language
0000 1001 1100 0110 1010 1111 0101 1000
1010 1111 0101 1000 0000 1001 1100 0110
1100 0110 1010 1111 0101 1000 0000 1001
0101 1000 0000 1001 1100 0110 1010 1111
5- 129
Binary (half) Addition
0
plus 0 is 0
 0 plus 1 is 1
 1 plus 0 is 1
 1 plus 1 is 0, carry a 1 to next column
1100
+
1
-----1101
Only good for first column.
5- 130
Binary (full) Addition, Handles
Other Columns
0
11
+ 11
----110
plus 0 plus 0 is 0
 0 plus 0 plus 1 is 1
 0 plus 1 plus 0 is 1
 0 plus 1 plus 1 is 0, carry a 1 to next column
 1 plus 0 plus 0 is 1
 1 plus 0 plus 1 is 0, carry a 1 to next column
 1 plus 1 plus 0 is 0, carry a 1 to next column
 1 plus 1 plus 1 is 1, carry a 1 to next column
These actions are carried out by circuits in the computer. 5- 131
Binary (half) Adder, Circuit
0
plus 0 is 0
 0 plus 1 is 1
 1 plus 0 is 1
 1 plus 1 is 0, carry
a 1 to next column
XOR
AND
AND
true
false
XOR
true
false
true
true
false
true
false
true
false
false
false
false
true
false
Where true is represented by a 1 (high voltage)
and false is represented by a 0 (low voltage)
5- 132
Binary (full) Adder, Circuit
AND
OR
AND
OR
AND
XOR
XOR
Calculating A plus B, where C is the
“carry bit” from the previous column (1 or 0)
There are many equivalent circuits that
compute this truth table / function
5- 133
0’s and 1’s
 What
 It
represents the 0’s and 1’s?
can be (and has been) many things…
 Voltages,
magnetic fields of various
kinds, physical relays that are open or
closed, vacuum tubes, transistors in
different states…
 Anything
that can be in two welldifferentiated states, and that can be
easily/quickly switched between the
states.
5- 134
The Layers of Computing
Application
Layer
Software
Browser Compiler Games
Utilities
System
Layer
Software
UNIX
Windows
Apple
System
Machine
Layer
Software
Assembly
Languages
Machine
Languages
MicroPrograms
Underlying
hardware
Memory
Screen
CPU
Hard disk
Keyboard
5- 135
The "Classic" Computer
Architecture
Screen - Output
Hard disk
CPU
Memory
Keyboard - Input
5- 136
The "Classic" Typewriter
Architecture
Paper - Output
Direct Mechanical Action
Keyboard - Input
5- 137
What Makes the Computer
Different?
 Memory
Short-term
Long-term
 Programmable
Multi-purpose
 Communication-enabled
5- 138
History
 People
have wanted
to have machines to
help them calculate
for thousands of
years
 These aspirations
began to be more
grandiose with the
advent of the
industrial revolution
5- 139
“Calculating Machine” or
“Mechanical Brain”?
 At
first, people thought of these
machines as very fast calculators
 The desire was to make them be
programmable, general purpose
calculators
 One turning point was to realize that
the program could be represented as a
number, and placed into the
computer’s memory, making it much
easier to re-program the very fast
calculator
5- 140
“Calculating Machine” or
“Mechanical Brain”?
 But
the really important turning
point (which did not happen all at
once) was to realize that these
machines could be more than
calculators – if almost everything
could be represented as numbers,
and they could manipulate
numbers, they could carry out all
sorts of actions that we don’t
normally associate with numbers
5- 141
ASCC Mark I, "Automatic
Sequence-Controlled
Calculator"
Built at Harvard by Howard
Aiken, completed January 1943
 Approaching architecture of a
modern computer
 Used mechanical
electromagnetic relays for
storing numbers and doing
calculations
 The machine was 51 feet long,
weighed 5 tons, and
incorporated 750,000 parts. It
included 72 accumulators

5- 142
ENIAC, the “first large-scale,
all-electronic, general purpose,
digital computer”
Eckert and Mauchly, University of
Pennsylvania, November 1945
 ENIAC's architecture resembles that of the
Harvard Mark I, but its components are
entirely electronic, incorporating 17,468
vacuum tubes
 The machine weighs 30 tons, covers about
1000 square feet of floor, and consumes
130 kilowatts of electricity; it uses vacuum
tubes

5- 143
ENIAC
 The
machine incorporates 20
accumulators (the original plan
was for 4). Each accumulator
stores a 10-digit number, using 10
bits to represent each digit.
 A separate unit can perform
multiplication (in about 3
milliseconds), while another does
division and square roots
5- 144
ENIAC
A
card reader is available to input
data values, and there is a card
punch for output
 The program is set up on a
plugboard --- this is considered
reasonable since the same or
similar program would generally be
used for weeks at a time
 The ENIAC's clock speed is 100 kHz
5- 145
ENIAC
5- 146
More ENIAC
5- 147
EDVAC, "Electronic Discrete
Variable Automatic Computer"
EDVAC was the first stored program computer
Oppenheimer and von Neumann
5- 148
EDSAC, Electronic Delay Storage
Automatic Computer
 Based
on EDVAC report, first full-scale
operational stored program computer,
May 1949
 16 tanks of mercury give a total of 256 35bit words (or 512 17-bit words)
 The clock speed of the EDSAC is 500 kHz;
most instructions take about 1500 ms to
execute
 Its I/O is by paper tape, and a set of
constant registers is provided for booting
5- 149
Things You Wish You Hadn’t Said
The United States will need a total of six
electronic digital computers
– Howard Aiken, developer of Mark I, 1947
“Computers in the future may weigh no
more than 1.5 tons”
– article in Popular Mechanics, 1949
5- 150
Lots More History
 Brattain,
Bardeen, and Shockley
invent the transistor, which eventually
replaces vacuum tubes, Dec. 1947
 Noyce
invents the integrated circuit,
which puts multiple connected
transistors onto a chip, January 1959
 Hoff
invents programmable computer
on a chip, Intel 4004, 1970
5- 151
Inventor of Intel 4004 Computer-ona-Chip, Marcian Hoff
5- 152
Intel 4004
 2250
transistors on the chip
 Processed 4 bits of data at a time
 600,000 operations a second
 Followed by (in Intel's line of chips)
the Intel 8008
 the 8080, the first chip that made a
personal computer possible
 the 8088, and the 8086, and the 80286,
80386, 80486, Pentium, Pentium II, III, IV ...

5- 153
Underlying Hardware—CPU

Central Processing Unit (CPU) — speed measured
using many different benchmarks
 Integer


performance, SPECint*_base2000
 Floating point performance, SPECfp*_base2000
 Entertainment benchmarks, internet benchmarks, …
Pentium, Pentium II, III, IV, PowerPC, Sun Sparc
See, for example,
http://www.intel.com/performance/resources/desktop/index.htm for
information about Pentium IV performance
5- 154
Underlying Hardware—RAM
Access Memory (RAM) — size
measured in megabytes or gigabytes
 Random
 Holds
programs while they are being
run
 2003
desktop computer might have from
256 to 1024 megabytes of RAM; more
powerful computers can have much
more RAM
5- 155
Underlying Hardware—Hard Disk
disk holds programs “permanently”
(even while power is off)
 Hard
 2003
desktop computer might have
between 60 to 200 gigabytes of hard disk
storage
5- 156
Underlying Hardware —
Removable Media
Floppy disks, writeable CDs (CD-R) and DVDs
(DVD-R, DVD+R, DVD-RW, DVD+RW) and tape
allow data to be backed up or transferred from
one computer to another
 Zip drives, 1 gigabyte Jaz drives (Iomega), dual
purpose MP3 hard-disk based players like the
iPod, flash memory up to 128MB or 256MB are
common (MemoryStick, CompactFlash, Secure
Digital, MultiMediaCard), …

5- 157
Underlying Hardware —
Input/Output Devices
 Input
devices, like a keyboard and a
mouse (and a microphone, and a joystick,
and a trackball, and a pen, and a scanner,
and…)
 Output devices, like a screen and a
printer (and a speaker, and a plotter, and
a laser printer, and…)
5- 158
A Brief Diversion
 Doug
Engelbart, the inventor of the mouse
(and windowed interfaces, and more):
http://www2.bootstrap.org/history.htm
The first mouse:
5- 159
Input Devices that didn't
take off
 The
chord key set:
5- 160
Names you probably don't know

Short History of the Internet
http://www.umr.edu/~dunaw/net-history.html

Paul Baran, of the RAND Corporation,
commissioned by the U.S. Air Force to do a
study on how it could maintain its
command and control over its missiles and
bombers, after a nuclear attack. Suggested
a packet-switched network.
http://www.umr.edu/~dunaw/net-history.html


Leonard Kleinrock, UCLA researcher who
connects computer to switch to another
computer, 2 September 1969
Ray Tomlinson, BBN engineer who invents
inter-machine email in 1972, "a quick hack",
chooses the @
http://www.pretext.com/mar98/features/story2.htm
5- 161
Typical Desktop Hardware
Configuration, 2003
 Pentium
IV processor, running at 3.06 GHz
 1 gigabyte of RAM
 Flat screen LCD 15” color monitor
 Built-in ethernet and modem
 CD-RW, DVD-RW drives
 160 gigabyte hard disk
 Approximate cost in U.S.: $1300
5- 162
Typical Desktop Hardware
Configuration, 1984
 IBM
AT 80286 processor, running
at 6 MHz
 256 KB of RAM, expandable to
3MB using five expansion cards
 Monochrome monitor (color
graphics card)
 20 MB hard disk
 Approximate cost in U.S.: $6600
5- 163
Hardware Comparison, 1984 –2003





IBM AT 80286
processor, running at
6 MHz
256 KB of RAM,
expandable to 3MB
using five expansion
cards
Monochrome monitor
(color graphics card)
20 MB hard disk
Approximate cost in
U.S.:
$6600
• Pentium IV processor, running
at 3.06 GHz
• 1 gigabyte of RAM
• Flat Screen LCD 15” color
monitor
• Built-in ethernet and modem
• CD-RW, DVD-RW drives
• 160 gigabyte hard disk
• Approx. cost in U.S.: $1300
Price/performance ratio
improvement, factor of over 8000
5- 164
Moore’s Law
 The
computing power available at a fixed
price will double every 18 months

“Moore…affirmed he never said transistor count would double
every 18 months, as is commonly said. Initially, he said transistors
on a chip would double every year. He then recalibrated it to every
two years in 1975. David House, an Intel executive at the time, noted
that the changes would cause computer performance to double
every 18 months.
“House actually came close. Computer power is doubling around
every 20 months. Nonetheless, ‘House said 18 months, not me,’
Moore said.
“The observation has also proved much more resilient than Moore
thought. ‘I never expected it to be precise. It turned out to be much
more precise than I ever imagined,’ he said.” – CNet, 11 Feb 2003
5- 165
The Meaning of
Exponential Growth
 This
has been true for over the last 35
years, and will continue to be true in
coming years
 Most
people cannot grasp the real
meaning of exponential growth,
confusing it with linear growth at a
sharp angle over the short term
5- 166
Exponential Growth, Doubling
Every Time Interval, 1, 2, 4, 8, 16, 32, …
1200
1000
800
600
400
200
0
1
2
3
4
5
6
7
8
9
10
11
5- 167
Exponential Growth, Doubling
Every 18 months, 1973 = 1, 2003 = 1048576
Exponential Growth
1200000
1000000
800000
600000
400000
200000
20
03
20
00
19
97
19
94
19
91
19
88
19
85
19
82
19
79
19
76
19
73
0
Year
5- 168
If Cars Improved the Way
Computers Do
A
Rolls Royce would cost $1 and travel
5000 kilometers on a liter of gasoline
 But it would be too small to get into
 Really:
$20,000 in 1968
 $5,000 in 1971
 $1,250 in 1974
 $0.0025 in 2003

5- 169
The Future of the IPod
Hard disk holding 40 GB
 $400 in 2003
 $100 in 2006
 $25 in 2009
 $6.25 in 2012
 ~ $1.50 in 2015
 ~ $0.40 in 2018
5- 170
Why We Don’t Notice It
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
2002
2005
We are focused on short periods, where the difference
between linear and exponential is obscured
5- 171
Exponential Growth, Doubling
Every 18 months, 1973 = 1, 2003 = 1048576
Exponential Growth
1200000
1000000
800000
600000
400000
200000
20
03
20
00
19
97
19
94
19
91
19
88
19
85
19
82
19
79
19
76
19
73
0
Year
5- 172
But the Future is Just as Amazing
1200
1000
800
600
400
200
0
2003
2003 = 1
2006
2009
2006 = 4
2012
2015
2018
2018 = 1024
5- 173
Two Curves
powerful
weak
then
The Hardware Curve
now
then
The Software Curve
now
powerful
weak
5- 174
Two Major Developments
 The
two biggest developments in the
computer industry in the last 5 years:

The transition of the computer from a
computing device to a communications
and computing device

The ever-shrinking, ever-cheaper
computing power has led to
“computers everywhere”, digital
appliances, embedded and standalone
5- 175
People are Thinking about the
End of Moore’s Law…

Intel researchers publish paper in Proceedings of the
IEEE, November 2003, predicting fundamental limits of
Moore’s Law to be reached in roughly 20 years

http://news.com.com/2100-7337-5112061.html?tag=nefd_lede

“Manufacturers will be able to produce chips on the
16-nanometer manufacturing process, expected by
conservative estimates to arrive in 2018, and maybe
one or two manufacturing processes after that, but
that’s it…In chips made on a 16-nanometer technology
process, the transistor gate will be about 5
nanometers long” (a nanometer is a billionth of a
meter)
This is a limitation of physics (tunneling of electrons
through the gate of a transistor), not of any particular
material used to make the transistor

5- 176
Where Does it End?

Two papers by Harvard and Cornell researchers
in the June 13, 2002 issue of the journal Nature
described a breakthrough in miniaturization:
researchers have created transistors whose
switching components are literally single atoms
(but they lack “gain” and work just at very low
temperatures).

What happens when the physical limits are
reached? Does the hardware curve straighten
out? Do new technologies (optical computing,
DNA computing, quantum computing) provide
new solutions?
5- 177
The Layers of Computing
Application
Layer
Software
Browser Compiler Games
Utilities
System
Layer
Software
UNIX
Windows
Apple
System
Machine
Layer
Software
Assembly
Languages
Machine
Languages
MicroPrograms
Underlying
hardware
Memory
Screen
CPU
Hard disk
Keyboard
5- 178
Machine Layer Software
language instructions —
built into the computer, a language
of 1’s and 0’s
 Machine
language instructions —
use brief English-like mnemonics
that carry out slightly more
complicated instructions. Assembly
language is directly and easily
translatable into machine language,
using an assembler
 Assembly
5- 179
Machine Layer Software (II)
 Nowadays,
there is less of a distinction
between machine language and
assembly language
 Computers are built that have “built-in”
translators
 Microcode—a machine language
program built into the CPU—is run
when an assembly language command
is given. So the assembly language is
the machine language!
5- 180
The Layers of Computing
Application
Layer
Software
Browser Compiler Games
Utilities
System
Layer
Software
UNIX
Windows
Apple
System
Machine
Layer
Software
Assembly
Languages
Machine
Languages
MicroPrograms
Underlying
hardware
CPU
Memory Hard disk Keyboard
5- 181
System Layer Software
 The
machine layer software is very
low level—we need a second layer
of software to take care of details
 The
operating system is a
constantly running program that:
keeps
seems
track of computer resources
to be controlling the computer
5- 182
System Layer Software —
the Operating System
 The
operating system:
“Listens”
to keyboard and mouse for input
“Talks” to screen and printer
Interprets commands as they are input
Makes programs available to the user and lets
him install new ones
Stores information in files, and manages them
Controls access to the computer
Splits CPU’s attention between several jobs
Communicating with other computers
5- 183
Lots of Operating Systems
 But
there are three most popular ones
today:
UNIX (and its Linux variant)
Windows (‘98, NT, XP)
Apple Macintosh OS X (built on top of Unix)
 They
differ in big and small ways—
timesharing, graphical interface, power…
 Also,
embedded systems and handhelds
5- 184
What’s the Connection?
 Question:
What’s the relationship between
an operating system and hardware?
 Answer: Not much, even though each
operating system has a “most common”
implementation on particular hardware:
Windows
on 80x86 chips, but Windows NT on
others
Macintosh on 680x0 chips and PowerPC chips
UNIX on SPARC chips, but also on 80x86 chips
and 680x0 chips…and others
5- 185
My Favorite Unix Quotes
 “Unix
is an operating system for
people who wish that they,
themselves, were computers.”
– Ralph Gorin
 “Contrary to popular belief, Unix
is user friendly. It just happens to
be selective about who it makes
friends with.”
– Dave Parnas
5- 186
What’s a GUI?
A
Graphical User Interface is
commonplace in computing these
days
 The
Apple Macintosh has it, machines
with Microsoft Windows have it, the
Xerox Star had it, Unix machines have
it (in many flavors)
A
graphical interface contrasts with a
character-based interface, such as
MS-DOS or plain Unix gives you
5- 187
Graphical User Interface
 The
GUI runs on top of the
Operating System, and makes the
Operating System easier to use
 Usually
includes: bitmapped
displays, menus, windows, use of
a pointing device (like a mouse),
buttons, etc.
5- 188
Windows XP
5- 189
The Layers of Computing
Application
Layer
Software
Browser Compiler Games
Utilities
System
Layer
Software
UNIX
Windows
Apple
System
Machine
Layer
Software
Assembly
Languages
Machine
Languages
MicroPrograms
Underlying
hardware
CPU
Memory Hard disk Keyboard
5- 190
Application Layer Software
 These
are the programs that do
specific jobs—word processors,
drawing programs, spreadsheet,
tax programs, etc.
are written in
any convenient language—
Pascal, C, Lisp, Modula-2,
Ada, Fortran…
Applications
 Applications
Programming Language
Operating System
 The
underlying platform is usually
a specific operating system
5- 191
Computer Programming
 The
history of computer
programming is a steady
move away from machineoriented views of
programming towards
concepts and metaphors that
more closely reflect the way
in which we ourselves
understand the world
5- 192
Programming progression…

Programming has progressed
through:
 machine
code
 assembly language
 machine-independent
programming languages
 procedures & functions
 objects
5- 193
Programming Languages
 Low
level (first or second
generation languages) are closely
tied to the computer’s instruction
set. They are good when:
the
program must control some
hardware that can only be controlled
in this low-level language
the
program must run extremely
quickly
5- 194
Machine language – Mark I
5- 195
Machine Language
0000 1001 1100 0110 1010 1111 0101 1000
1010 1111 0101 1000 0000 1001 1100 0110
1100 0110 1010 1111 0101 1000 0000 1001
0101 1000 0000 1001 1100 0110 1010 1111
5- 196
Assembly Language – PDP-11
5- 197
Assembly Language –
Macro-11
GCD:
SIMPLE:
TST
BEQ
MOV
SXT
DIV
MOV
MOV
CALL
RETURN
B
SIMPLE
A, R5
R4
B, R4
B, A
R5, B
GCD
5- 198
Assembly Language –
Macro-11
GCD:
SIMPLE:
TST
BEQ
MOV
SXT
DIV
MOV
MOV
CALL
RETURN
B
SIMPLE
A, R5
R4
B, R4
B, A
R5, B
GCD
5- 199
A Computer Command in
Machine Language
data movement
address movement
integer arithmetic
floating arithmetic
binary coded decimal
advanced math
data conversion
logical
shift and rotate
bit manipulation
character and string
table operations
high level language support
program control
condition codes
input/output
MIX devices
system control
coprocessor and multiprocessor
trap generating
5- 200
Higher-level Languages
 Higher
level languages (third
generation languages) like Pascal, C,
C++, Java, etc. are more disconnected
from the hardware on which they run
 They
can be used to solve any kind of
problem
 They
can run on any kind of computer
5- 201
Machine-Independent Programming
Languages – Fortran
! This example program solves for roots of the quadratic equation,
! ax^2 +bx +c =0,for given values of a, b and c.
!
PROGRAM bisection
IMPLICIT NONE
INTEGER :: iteration
DOUBLE PRECISION :: CC, Er, xl, x0, x0_old, xr
! Set convergence criterion and guess for xl, xr.
CC = 1.d-4
xl = 8.d-1
xr = 11.d-1
! Bisection method.
Er =CC +1
iteration = 0
DO WHILE (Er > CC)
iteration = iteration + 1
! Compute x0 and the error.
x0_old = x0
x0 = (xl + xr) / 2.d0
Er = DABS((x0 - x0_old)/x0)*100.d0
WRITE (*,10) iteration, x0_old, x0, Er
10 FORMAT (1X,I4,3(2X,E10.4))
this is partial…
5- 202
Procedures & Functions –
Pascal
program ValueArg(output);
{Shows how to arrange for a procedure to have arguments.}
procedure PrintInitials(First, Last : char);
{Within this procedure, the names First and Last represent the
argument values. We’ll call write to print them.}
begin
write(‘My initials are: ’);
write(First);
writeln(Last)
end; {PrintInitials}
begin
PrintInitials (‘D’, ‘C’); {Any two characters can be arguments.}
PrintInitials (‘Q’, ‘T’); {Like strings, characters are quoted.}
PrintInitials (‘&’, ‘#’)
end. {ValueArg}
5- 203
Java
 Designed
by Sun team led by James
Gosling
 Originally
called Oak, it was intended for
consumer devices like TV-top boxes
 Being
cross platform, and more stable
than C++, were essential goals
 When
the TV-top market didn’t
materialize, figured they’d try the internet
5- 204
Object Oriented Programming
(This example from Java)
class Time {
private int hour, minute;
public Time (int h, int m) {
hour = h;
minute = m;
}
public void addMinutes (int m) {
int totalMinutes =
((60*hour) + minute + m) % (24*60);
if (totalMinutes<0)
totalMinutes = totalMinutes + (24*60);
hour = totalMinutes / 60;
minute = totalMinutes % 60;
}
}
this is partial…
5- 205
“Intrinsic Power” vs.
“Effective Power”

This progression is not a matter of “intrinsic power”

Anything you can do with a minimally capable
computer language, you can theoretically do with any
other minimally capable computer language

But that is like saying a shovel is theoretically as
capable as a tractor. In practice, using a shovel might
make things very hard…
5- 206
Fourth Generation Languages
 Application
languages (fourth
generation) are more high level
languages, but also more specialized
 Examples are PostScript, database
languages, etc.
 They are very good at the tasks they
do, and clumsy for general-purpose
tasks
5- 207
Some PostScript Code
%!PS-Adobe-3.0 EPSF-2.0
%%Creator: Windows PSCRIPT
%%Title: PowerPoint - UNIT5.PPT
%%BoundingBox: 13 10 577 832
%%DocumentNeededResources: (atend)
%%DocumentSuppliedResources: (atend)
%%Pages: 0
%%BeginResource: procset Win35Dict 3 1
/Win35Dict 290 dict def Win35Dict begin/bd{bind def}bind def/in{72
mul}bd/ed{exch def}bd/ld{load def}bd/tr/translate ld/gs/gsave ld/gr
/grestore ld/M/moveto ld/L/lineto ld/rmt/rmoveto ld/rlt/rlineto ld
/rct/rcurveto ld/st/stroke ld/n/newpath ld/sm/setmatrix ld/cm/currentmatrix
ld/cp/closepath ld/ARC/arcn ld/TR{65536 div}bd/lj/setlinejoin ld/lc
/setlinecap ld/ml/setmiterlimit ld/sl/setlinewidth ld/scignore false
def/sc{scignore{pop pop pop}{0 index 2 index eq 2 index 4 index eq
and{pop pop 255 div setgray}{3{255 div 3 1 roll}repeat
setrgbcolor}ifelse}ifelse}bd
/FC{bR bG bB sc}bd/fC{/bB ed/bG ed/bR ed}bd/HC{hR hG hB sc}bd/hC{
5- 208
The Field of Computer Science
 We’ve
been looking at computers
(software and hardware), but
that’s not an accurate description
of the field of Computer Science:
Hardware
Software
Theory
5- 209
Areas in Computer Science










Algorithms and Data Structures
Programming Languages
Computer Architecture
Operating Systems
Software Engineering
Symbolic and numerical computation and
modeling, graphics
Databases
Artificial Intelligence
Robotics
Computer Vision
5- 210
How they fit together
Hardware
Architecture
Software
Theory
Languages
Algorithms
Software
Engineering
Operating
Systems
Databases
Robotics
Symbolic/Numerical
Computation
Artificial Intelligence
5- 211