chapter 1

1. AN OVERVIEW OF
COMPUTERS &
PROGRAMMING
LANGUAGES

2. GOALS
 To understand the activity of programming
 To learn about the components of computers
 To learn about level of programming languages
 To become familiar with your computing
environment and your compiler
 To compile and run your first Java program
 To recognize 3 types of errors

3. What is Programming?
 Computer programming
 the art and science of designing and writing
computer programs.
 Computer program
 a sequences of instructions written in a
programming language to achieve a task/to solve
a problem.

4. What is a computer?
 Hardware
 the physical, tangible parts of a computer
 keyboard, monitor, disks, wires, chips, etc.
 Software
 programs and data
 a program is a series of instructions
 A computer requires both hardware and software
 Each is essentially useless without the other

5. Computer System Organization
Hardware
•CPU
•Main Memory (RAM)
•Secondary Storage
•I/O Device
Software
•System Programs
•Application Programs
Computer Organization

6. Hardware Components
of a Computer

7. Hardware Components
of a Computer – motherboard
processor chip
adapter cards
memory chips
memory slots
motherboard
Expansion
slots for
adapter cards

8. Hardware Components of a Computer
CPU
Brain of the
computer, most
expensive, the
faster computer.
CPU components–
control unit,
program counter,
register instruction,
arithmetic logic
unit, accumulator.
RAM
Temporary memory,
volatile, directly
connected to the
CPU, using
memory cells unit.

9. SECONDARY STORAGE
•Provides permanent storage for
information.
•Examples of secondary storage:
•Hard disks
•Floppy disks
•Zip disks
•CD-ROMs
•Tapes.
Hardware Components of a Computer

10. RAM vs Secondary Storage
 Primary memory
 volatile
 Fast
 Expensive
 Low capacity
 Works directly with the processor
 Secondary Storage
 Nonvolatile
 Slow
 Cheap
 Large capacity
 Not connected directly to the processor

11. INPUT DEVICES
Sheet-fed
Hardware Components of a Computer

12. OUTPUT DEVICES
Hardware Components of a Computer

13. CPU and Main Memory
Central
Processing
Unit
Main
Memory
Chip that executes
program commands
Eg.
Intel Pentium 4
Sun ultraSPARC III
Primary storage area
for programs and data
that are in active use
Synonymous with
RAM

14. Secondary Memory Devices
Central
Processing
Unit
Main
Memory
Floppy Disk
Hard Disk
Secondary memory
devices provide
long-term storage
Information is moved
between main memory
and secondary memory
as needed
Hard disks
Floppy disks
USB drives
Writable CDs
Writable DVDs
Tapes

15. Input / Output Devices
Central
Processing
Unit
Main
Memory
Floppy Disk
Hard Disk
Monitor
Keyboard
I/O devices facilitate
user interaction
Monitor screen
Keyboard
Mouse
Joystick
Bar code scanner
Touch screen

16. Software
 In contrast to hardware, software is an abstract, intangible
entity.
 Software can be categorized as system or application
software (refer next slide)
 It consists of program and data to be used to perform
certain tasks
 A program is a sequence of simple steps and operations,
stated in a precise language that the hardware can interpret
 The process of programming involve algorithm design &
coding.

17. Software Categories
 System Software
 Systems programs keep all the hardware and software running
together smoothly
 The most important system software is the operating system (OS)
 controls all machine activities
 provides the user interface to the computer
 manages resources such as the CPU, memory & I/O
 Windows XP, Unix, Linux, Mac OS
 Application Software
 generic term for any other kind of softwares
 word processors, Spreadsheets, Web browsers, games

18. Algorithm
Algorithm refers to the strategy to solve a problem
It is a clear step by step sequence of instructions that
describes how to accomplish a certain task.
2 ways can be used to represent algorithm:
a) pseudocode
- using english-like-phrases to describe the
algorithm
b) flowchart
-using diagrams that employ the
symbol to describe the algorithm.

19. Coding
Algorithm need to be translated into computer
language so that it can be executed
Coding refers to the process of expressing
algorithm in a programming language
The product of coding is a program.
The act of carrying out the instructions contained
in a program is called program execution
 A computer program is stored internally as a
series of binary numbers known as the machine
language of the computer

20. Digital Information
 Computers store all information digitally:
 numbers
 text
 graphics and images
 video
 audio
 program instructions
 In some way, all information is digitized - broken
down into pieces and represented as numbers

21. Representing Text Digitally
 For example, every character is stored as a
number, including spaces, digits, and punctuation
 Corresponding upper and lower case letters are
separate characters
H i , H e a t h e r .
72 105 44 32 72 101 97 116 104 101 114 46

22. p. 4.15 Fig. 4-16 Next
The ASCII data set  128 characters (0 until 127)
Character A in ASCII  01000001
American Standard Code for Computer
InterChange (ASCII)

23. Binary Numbers
 Once information is digitized, it is represented
and stored in memory using the binary number
system
 A single binary digit (0 or 1) is called a bit
 A byte consists of 8 bits.
 Each byte in main memory resides at a
numbered location called its address.

24. Memory
24
Main memory is divided
into many memory
locations (or cells)
9278
9279
9280
9281
9282
9283
9284
9285
9286
Each memory cell has a
numeric address, which
uniquely identifies it

25. Storing Information
25
9278
9279
9280
9281
9282
9283
9284
9285
9286
Large values are
stored in consecutive
memory locations
10011010
Each memory cell stores a
set number of bits (usually
8 bits, or one byte)

26. Main Memory

27. Storage Capacity
 Every memory device has a storage capacity,
indicating the number of bytes it can hold
 Capacities are expressed in various units:
27
KB 2
10
= 1024
MB 2
20
(over 1 million)
GB 2
30
(over 1 billion)
TB 2
40
(over 1 trillion)
Unit Symbol Number of Bytes
kilobyte
megabyte
gigabyte
terabyte

28. Language Levels
 Levels of programming language levels:
 machine language
 assembly language
 high-level language
 Each type of CPU has its own specific
machine language
 The other levels were created to make it easier
for a human being to read and write programs
28

29. Programming Languages
Machine language
101101100110 011011010
Assembly language
iload intRate
bipush 100
if_icmpgt intError
High-level language
if (intRate > 100) . . .

30. Programming Languages
 Each type of CPU executes instructions only in a
particular machine language
 A program must be translated into machine
language before it can be executed
 A compiler is a software tool which translates from
high level language into a specific machine
language
 An assembler translates from assembly language
into a specific machine language
30

31. Language Description Examples Translator
Machine Instruction in 0
and 1 bits
0111000011000
001
None
Assembly Instruction in
mnemonic code
LOAD 3
STOR 4
ADD
assembler
High-level Similar to human
language,
FORTRAN,
COBOL, Pascal,
C, C++, Java…
sum = 4 + 3; Compiler &
interpreter
Programming Languages

32. The Java Programming Language
 Created by Sun Microsystems, Inc.
introduced in 1995 and it's popularity has
grown quickly since
Rich library
Platform-independent ("write once, run
anywhere") or architecture-neutral

33. Java Translation
 The Java compiler translates Java source code
into a special representation called bytecode
 Java bytecode is not the machine language for any
traditional CPU
 Another Java software tool, called an interpreter
(or Java Virtual Machine (JVM)) , translates
bytecode into machine language and executes it
33

34. Java Translation
34
Java source
code (program)
Machine
code
Java
bytecode
Bytecode
interpreter
Java
compiler

35. Portability
 After compiling a Java program into byte-code, that
byte-code can be used on any computer with a byte-
code interpreter and without a need to recompile.
 Byte-code can be sent over the Internet and used
anywhere in the world.
 This makes Java suitable for Internet applications.

36. Becoming Familiar with your
Computer to use Java
 Understand files and folders/directories
 Locate the Java compiler/ Install J2SE
 Set path & Java class path
 Write a simple program (later)
 Save your work
 Compile & run
 Use Dos Command Prompt or IDE

37. A DOS Command Window

38. An Integrated Development
Environment

39. File Hello.java
1 public class Hello
2 {
3 public static void main(String[] args)
4 {
5 // display a greeting in the console window
6 System.out.println("Hello, World!");
7 }
8 }

40. Java Program Elements
 A Java program is made up of class definitions.
 A class definition must contains a header and a
body.
 A class contains zero or more methods
 A method is a named section of code that also has
a header & body
 A method contains program statements
 Single-line (starts with //) and multi-line (enclosed
by /* and */) comments are used to document the
code

41. Java Program Structure
41
public class Hello
{
}
// comments about the class
class header
class body
//Comments can be placed almost anywhere

42. Java Program Structure
42
public class MyProgram
{
}
// comments about the class
public static void main (String[] args)
{
}
// comments about the method
method header
method body

43. Compiling and Running
Type program into text editor
Save (file name must be similar to class name)
Open Dos Window
Change directory to saved file directory
Compile into byte codes
javac Hello.java
Execute byte codes
java Hello

44. Hello.java
javac
Hello.class
java
Class Loader
Processing a Java Program

45. Class Loader
 A Java program typically consists of several pieces
called classes.
 Each class may have a separate author and each is
compiled (translated into byte-code) separately.
 A class loader (called a linker in other programming
languages) automatically connects the classes
together and loads the compiled code (bytecode) into
main memory.

46. JVM
Create/modify source code
Source code
Compile source code
Byte code
Run byte code
Output
Syntax errors
Runtime errors or
incorrect results
Creating a Java Program…

47. Errors
 It is common for programmer to make mistake
in a program.
 Three kinds of errors
 Syntax errors
 Runtime errors
 Logic errors

48. Syntax Errors
 Grammatical mistakes in a program
 The grammatical rules for writing a program are very
strict
 The compiler catches syntax errors and prints
an error message.
 Example: using a period where a program
expects a semicolon
 System.out.print("..."),
 System.out.print("Hello);

49. Runtime Errors
 Errors that are detected when your program is
running, but not during compilation
 When the computer detects an error, it
terminates the program and prints an error
message.
 Example: attempting to divide by 0

50. Logic Errors
 Errors that are not detected during compilation or
while running, but which cause the program to
produce incorrect results
 Example: an attempt to calculate a Fahrenheit
temperature from a Celsius temperature by
multiplying by 9/5 and adding 23 instead of 32
 E.g
 System.out.print("Hell");