1. OBJECT ORIENTED PROGRAMMING I LECTURE 2 GEORGE KOUTSOGIANNAKIS
CS 115
OBJECT ORIENTED PROGRAMMING I
LECTURE 2
GEORGE KOUTSOGIANNAKIS
Copyright: Fall Illinois Institute of Technology-
George Koutsogiannakis

2. NOTE
MAKE SURE THAT YOU HAVE YOUR TEXT WITH YOU IN EVERY LECTURE!!

3. Basic Computer Concepts
Hardware
Central Processing Unit
Memory and Storage Devices
Operating Systems
Application Software
Computer Networks and the Internet

4. Typical Computer Hardware
CPU
executes the instructions of the program
Hard disk and CD-ROM
store instructions and data so program can be loaded into memory and executed
Main memory
stores the program instructions and data while executing
Keyboard and mouse
used for data input
Monitor
used to display output from a program
Other accessories, such as a printer

5. A Typical Design of a Personal Computer

6. Central Processing Unit (CPU)
Arithmetic Logic Unit
performs integer arithmetic and logical operations
Floating-point Unit
performs floating-point operations
Hardware registers
store data and memory addresses
Instruction Pointer
keeps track of next instruction to execute
Examples of CPUs:
Intel Core 2 Duo™, AMD Turion™ 64, Sun Microsystems SPARC, Hewlett-Packard PA-RISC, IBM POWER processor

7. CPU Instructions Move data from one location to another
Perform a calculation
Compare data
Change the sequence of instructions to execute (the flow of control)

8. Memory or Storage Devices
Memory consists of cells that hold one bit.
A bit's value can be 0 or 1
A byte is 8 binary digits (bits)
Storage capacity is expressed as:
Kilobytes (1,024 bytes)
Megabytes (1,048,576 bytes)
Gigabytes (1,073,741,824 bytes

9. Operating System (OS) Software
OS boots when computer is turned on, and runs continuously
Controls the peripheral devices (disks, keyboard, mouse, etc.)
Supports multitasking (multiple programs executing simultaneously)
Allocates memory to each program
Prevents one program from damaging another program
Controls the file system. Hard drive storage/file opening for writing/ file opening for reading/closing of files/allocating resources needed for file operations.
OS Examples: Microsoft Windows, Linux

10. Application Software Written to perform specific tasks
Runs "on top of" the operating system
Examples: word processor, spreadsheet, database management system, games, Internet browser, etc.

11. Data Representation
Computer data is stored in the form of binary numbers.
Binary Numbers
Expressed in base 2 system
(two values are: 0 and 1)
Hexadecimal Numbers
Base-16 system used as shorthand for representing binary numbers
The Unicode Character Set
Used to represent characters. Every character is represented by a coded number.
You can find out more about the coded numbers by going to web site:

12. Binary Equivalents of Decimal Numbers
Decimal Binary Equivalent

13. Powers of 2
Decimal Decimal , , , , , ,768

14. Decimal (base 10) numbers
A decimal number can be represented as the sum of powers of 10 (the base) with coefficients in the base 10 digits (0 - 9)
For example:
2485 =
2485 = 2 * * * * 1
2485 = 2 * * * * 100

15. Converting From Decimal to Binary
Just as a decimal number can be represented as a sum of powers of 10 (the base) with coefficients in the base 10 alphabet (0 to 9) we can change the representation:
A number can also be represented as the sum of powers of 2 (the base of the binary system) with coefficients in the base 2 digits (0 and 1).
Since we change the base to 2 instead of 10 we will call that representation of the number: a binary number
To make the conversion from a base of 10 top a base of 2 we need an algorithm to do that.
We can also start with a base of 2 representation of a number (a binary number) and then convert it back to a base of 10 (make it a decimal number).

16. BINARY TO DECIMAL CONVERSION -Example
Convert the binary number to decimal where the extreme right is the Least Significant binary number:
1*25+0*24+0*23+1*22+1*21+0*20
=0=38
3*101+8*100

17. DECIMAL TO BINARY CONVERSION -Example
To convert 38 back to the binary we keep dividing by two and keep the remainder:
38/2=19 remainder is 0 (LSB: least significant binary)
19/2=9 remainder is 1
9/2=4 remainder is 1
4/2=2 remainder is 0
2/2=1 remainder is 0
½=0 remainder is 1 (MSB : most significant binary)

18. DECIMAL TO BINARY CONVERSION -Example
Therefore the binary number is from MSB to LSM:
Notice that the representation is left to right where the MSB is on the left.
1*25+0*24+0*23+1*22+1*21+0*20

19. Hexadecimal Numbers Base-16 number system (16 digits)
Uses digits and letters A – F for remainder digits.
One hexadecimal digit can express values from 0 to 15
For example: C represents 12
Thus, one hexadecimal digit can represent 4 bits in a binary system.

20. Hexadecimal - Binary Equivalents
Hex Binary Decimal Hex Binary Decimal A B C D E F

21. The Unicode Character Set
Each character is stored as 16-bits
Maximum number of characters that can be represented: 65,536 (216)
ASCII character set (used by many programming languages) stores each character as 7 bits (maximum number of characters is 128)
For compatibility, first 128 characters of Unicode set represent the ASCII characters

22. Some Unicode Characters
Character Decimal Value Hex Value
* A A B a b
} D

23. Unicode system
Every key on the computer’s keyboard translates to a Unicode value.
The computer system understands what you typed from that translated Unicode value.
Keep in mind that there are other symbols that are not necessarily on the keyboard but they have a Unicode value.

24. Programming Languages
Machine language
Assembly language
High-level languages

25. High-Level Languages Examples: Fortran, Perl, COBOL, C++, Java
Highly symbolic
Portable among CPU architectures
Languages can be designed for specific uses:
Perl: Internet applications
Fortran: scientific applications
COBOL: business applications

26. A Java Program
We write programming instructions on a text editor using English words specific to the programming language (called keywords) and other English words that represent categories data (called identifiers). This is called the source code file
The source code (Programming instructions) gets translated by a compiler to coded instructions (coded binary numbers-sequences of 1s and 0s). The compiler produces a file called the bytecodes file.
The bytecodes file needs to be interpreted by the Java Interpreter in order for the instructions to be executed by the machine (the interpreter actually converts the coded java instrcutions into machine instructions).

27. High-Level Languages
Compiled- Some languages need only to compile the source code.
Compiler converts source code (instructions and data) into machine language directly, then program is executed
C language is such a language
Interpreted- Some languages (like Java) need also the interpeter.
Interpreter converts instructions into machine language at run time as instructions are executed
Usually executes more slowly than compiled program
Java needs both compilation and interpretation.

28. Java Therefore, Java uses a Combination of compiler and interpreter
Compiler converts source code into byte codes (an instruction set for a virtual, machine-independent processor). The instructions are intended for something called the JVM (Java Virtual Machine).
At run time, the Java Virtual Machine (JVM) interprets the byte codes and converts them into the machine language for the platform (CPU type and Operating System type)on which the program is running.

29. The Java Language Created by Sun Microsystems in 1995
Syntax is based on C++
Object-oriented. This term will be explained farther into the course.
Supports Internet applications
Provides an extensive library of prewritten classes
Is portable among platforms because of the JVM concept. The JVM is , however, specific to the platform.
Has built-in networking

30. Programming Basics
Programming is translating a problem into ordered steps consisting of operations a computer can perform:
Input
Perform calculations
Compare values
Move data
Output
The order of execution of instructions is called flow of control

31. Four Types of Flow of Control
Sequential Processing
Execute instructions in order
Method Call
Jump to code in method, then return
Selection
Choose code to execute based on data value
Looping or Iteration
Repeat operations for multiple data values

32. Sequential Processing
The pseudocode for calculating the sum of two numbers would look like this:
read first number
read second number
set total to (first number second number)
output total

33. Parts of a Java Program
The class (every Java program is inside a class)
A class can have methods. A method is that chunk of programming instructions usually dedicated to a specific task (for example some specific calculation)
Instance variables of the class. Those are specific data that the class needs to use.

34. What is a Class
A class is an artificial (conceptual) representation of the overall task that our Java program is supposed to accomplish.
We arbitrarily assign a name to that class
i.e.
public class CalculateMyExpenses
Don’t worry right now as to what public means.
The name of the class in the example is CalculateMyExpenses and obviously it signifies that my program is intended to calculate expenses.
The name is arbitrarily chosen.

35. Topics to be studied
The next few slides present the highlights of the topics that will be discussed in more detail as the course progresses.

36. What is a Class
Note: This is a first look at a what a class means to a Java program. We will come back to that to give more extensive definitions later on in the course!!!
Therefore our Java program always starts by defining a class name!!
The overall task that the program has to accomplish can be subdivided into smaller tasks.

37. Methods
Each of the smaller tasks, within the overall task that our program (class) has to accomplish , can be represented by a group of programming instructions that can accomplish that task. That group of instructions for that task constitutes what is called a “method” in Java.
One of the programming instructions within the group of instructions that a method has, can be an instruction that calls another method to execute its instructions (perform its task).
That is called a “method call” type of instruction.

38. Method Call Calling the method executes the method
Methods can take arguments (data to use) and return values (return data as a result of the method’s execution)
Here is pseudocode for calculating the square root of an integer:
  read an integer
call the square root method, passing the integer and receiving the square root
output the square root

39. Method Signature Here is an example of a method signature:
public return_type method_name (type1 name_of_type1, type2 name of type2)
Note: by the term signature we mean the way we have to write the method (the syntax that we have to use)
public indicates that the method can be called by any members of any class.
Followed that is the data type that the method returns to whoever called it
i.e. int, String etc.
it could be void also in which case the method does not return anything to the caller.
Followed the data type is the name of the method
Inside the parenthesis we find the arguments that method takes

40. Method Arguments
Arguments are the data types and their values that a caller of that method has to pass to the method.
Notice that there is no requirement to pass arguments to a method. It could be empty of arguments.
A method can call another method from within its code.

41. Example public class FirstProgram 5 {
5 {
6 public static void main( String [] args )
7 {
System.out.println( "Programming is not "
" a spectator sport!" );
System.exit( 0 );
11 }
12 }
Question:
Identify the methods their return values their arguments and any method calls made in this program.

42. Selection
The pseudo code for determining if a number is positive or negative is:
read a number
if the number is greater than or equal to 0
write "Number is positive."
else
write "Number is negative."

43. Looping The pseudocode for finding the sum of a set of numbers is:
set total to 0
read a number
while there was a number to read,
add number to total
read the next number
write total

44. Identifiers - Symbolic Names
Identifiers are used to name classes, variables, and methods
Identifier Rules:
Must start with a "Java letter"
A - Z, a - z, _, $, and Unicode letters
Can contain essentially any number of Java letters and digits, but no spaces
Case sensitive!!
Number1 and number1 are different
Cannot be keywords or reserved words

45. Program Building Blocks
The Statement
Performs some action
Terminates with a semicolon (;)
Can span multiple lines
Example:
System.out.println( “Programming is ”
+ “not a spectator sport” );

46. Building Blocks - The Block
0, 1, or more statements
Begins and ends with curly braces { }
Can be used anywhere a statement is allowed
Example:
public static void main( String [] args ) {
System.out.println( “Hello” ); }

47. Building Blocks - White Space
Space, tab, newline are white space characters
At least one white space character is required between a keyword and identifier
Any amount of white space characters are permitted between identifiers, keywords, operators, and literals
Examples:
int a
1 + 2
public static void main( String [] args)

48. Data Types, Variables, and Constants
For all data, assign a name (identifier) and a data type
Data type tells compiler:
How much memory to allocate
How to store the data
The types of operations you will perform on the data
Compiler monitors use of data
Java is a strongly typed language
Java eight primitive data types
byte, short, int, long, float, double, char, boolean

49. Examples Are these identifiers valid? taxRate char intNumber
Yes.
char
No. char is a keyword
intNumber
Yes, The keyword int is embedded, but the identifier is not identical to a keyword.
2008Taxrate
No. The identifier starts with a digit

50. Declaring Variables
Variables hold one value at a time, but that value can change
Syntax:
dataType identifier; or
dataType identifier1, identifier2, …;
Naming convention for variable names:
first letter is lowercase
embedded words begin with uppercase letter

51. Integer Types - Whole Numbers
Type Size Minimum Value Maximum Value
in Bytes
byte
short , ,767
int , 147, 483, , 147, 483, 647
long ,223,372,036,854,775, ,223,372,036,854,775,807
Example declarations:
int testGrade;
int numPlayers, highScore, diceRoll;
short xCoordinate, yCoordinate;
byte ageInYears;
long cityPopulation;

52. Text Study Guide
Chapter 1
Pages 1-32
Chapter 2
Pages 41-46