introduction to computer and java

AN OVERVIEW OF COMPUTERS &

PROGRAMMING LANGUAGES

AN OVERVIEW OF COMPUTERS &

PROGRAMMING LANGUAGES

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

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.

What is a computer? Hardware

the physical, tangible parts of a computerkeyboard, monitor, disks, wires, chips, etc.

Softwareprograms and dataa program is a series of instructions

A computer requires both hardware and software

Each is essentially useless without the other

Computer System Organization

Hardware•CPU•Main Memory (RAM)•Secondary Storage•I/O Device

Software•System Programs•Application Programs

Computer Organization

Hardware Components of a Computer

Hardware Components of a Computer – motherboard

processor chipadapter cards

memory chips

memory slots

motherboard

Expansionslots for adapter cards

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.

RAMTemporary memory, volatile, directly connected to the CPU, using memory cells unit.

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

RAM vs Secondary Storage Primary memory

volatileFast Expensive Low capacity Works directly with the processor

Secondary StorageNonvolatileSlow Cheap Large capacity Not connected directly to the processor

INPUT DEVICES

Sheet-fed

Hardware Components of a Computer

OUTPUT DEVICES

Hardware Components of a Computer

CPU and Main Memory

CentralProcessing

Unit

MainMemory

Chip that executes program commands

Eg.Intel Pentium 4Sun ultraSPARC III

Primary storage area for

programs and data that are in

active use

Synonymous with RAM

Secondary Memory Devices

CentralProcessing

Unit

MainMemory

Floppy Disk

Hard Disk

Secondary memorydevices providelong-term storage

Information is movedbetween main memoryand secondary memoryas needed

Hard disksFloppy disksUSB drivesWritable CDsWritable DVDsTapes

Input / Output Devices

CentralProcessing

Unit

MainMemory

Floppy Disk

Hard Disk

Monitor

Keyboard

I/O devices facilitateuser interaction

Monitor screenKeyboardMouseJoystickBar code scannerTouch screen

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.

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

Algorithm

Algorithm refers to the strategy to solve a problemIt 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 algorithmb) flowchart

-using diagrams that employ the symbol to describe the algorithm.

Coding

Algorithm need to be translated into computer language so that it can be executedCoding refers to the process of expressing algorithm in a programming languageThe 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

Digital Information Computers store all information digitally:

numberstextgraphics and imagesvideoaudioprogram instructions

In some way, all information is digitized - broken down into pieces and represented as numbers

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

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)

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.

Memory

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Main memory is divided into many memory locations (or cells)

927892799280928192829283928492859286

Each memory cell has a numeric address, which uniquely identifies it

Storing Information

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927892799280928192829283928492859286

Large values arestored in consecutivememory locations

1001101010011010Each memory cell stores a set number of bits (usually 8 bits, or one byte)

Main Memory

Storage Capacity Every memory device has a storage capacity,

indicating the number of bytes it can hold

Capacities are expressed in various units:

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KB 210 = 1024

MB 220 (over 1 million)

GB 230 (over 1 billion)

TB 240 (over 1 trillion)

Unit Symbol Number of Bytes

kilobyte

megabyte

gigabyte

terabyte

Language Levels Levels of programming language levels:

machine languageassembly languagehigh-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

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Programming Languages

Machine language101101100110 011011010

Assembly languageiload intRatebipush 100if_icmpgt intError

High-level languageif (intRate > 100) . . .

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

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Language Description Examples Translator

Machine Instruction in 0 and 1 bits

0111000011000001

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

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

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

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Java Translation

34

Java sourcecode (program)

Machinecode

Javabytecode

Bytecodeinterpreter

Javacompiler

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.

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

A DOS Command Window

An Integrated Development Environment

File Hello.java1 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 }

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 & bodyA method contains program statements

Single-line (starts with //) and multi-line (enclosed by /* and */) comments are used to document the code

Java Program Structure

41

public class Hello{

}

// comments about the class

class header

class body

//Comments can be placed almost anywhere

Java Program Structure

42

public class MyProgram{

}

// comments about the class

public static void main (String[] args){

}

// comments about the method

method headermethod body

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 codesjavac Hello.java

Execute byte codesjava Hello

Hello.java

javac

Hello.class

java

Class Loader

Processing a Java Program

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.

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…

Errors

It is common for programmer to make mistake in a program.

Three kinds of errorsSyntax errorsRuntime errorsLogic errors

Syntax Errors

Grammatical mistakes in a programThe 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);

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

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.gSystem.out.print("Hell");