Chapter 1 Introduction to computer and java

Weekly Report Chapter 1 Introduction to Computer and Java 1 Contents 1 Introduction 2 Why Program? 3 Computer Systems Hardware and Software 4 Programming Languages 5 What is a Program Made of? 6 The P.

Chapter 1

Introduction to Computer and Java

5 What is a Program Made of?

6 The Programming Process

7 Object-Oriented Programming

1 Introduction

 A powerful programming language

 Runs on every type of computer

 To create large or small applications

2 Why Program?

professions.

whatever job their programs, or

software , tell them to do.

2 Why Program? (Cont’d)

 Create software

program:

 The logical flow of the instructions

 The mathematical procedures

 The layout of the programming statements

 The appearance of the screens

 The way information is presented to the user

 The program’s ‘user friendliness’

 Manuals, help system, and/or other written

documentation

3 Computer Systems

 All computer systems consist of similar

hardware devices and software components.

 Hardware

 Refers to the physical components that a

computer made of.

 A typical computer system consists of:

 The central processing unit (CPU)

 Main memory

 Secondary storage devices

 Input devices

Hardware

Hardware (Cont’d)

 Central Processing Unit (CPU)

 CPU’s job:

 Fetch instructions

 Follow the instructions

 Produce some resulting data

 Consists of two parts:

 Control unit:

 coordinates all of the computer’s operation

 Arithmetic and logic unit (ALU)

performs mathematical operations

CPU (Cont’d)

 A program is a sequence of instructions

stored in the computer’s memory

 When a computer is running a program,

the CPU is engaged in a process known as

fetch/decode/execute cycle

 Fetch

 CPU fetches, from main memory, the next instruction

in the sequence of program instruction

 Main memory is commonly known as random

access memory (RAM)

 RAM is the computer’s main memory that

holds information:

 the sequences of instructions in the programs that are running

 the data those program are using

 RAM is usually a volatile type of memory

 is used only for temporary storage

 When the computer is turned off, the contents of RAM are erased.

Memory (Cont’d)

 is assigned a unique number known as an

Memory (Cont’d)

Secondary Storage

 Secondary storage is a type of memory

 Can hold data for long periods of time – even when there is no power to the computer

 Programs are usually stored in secondary

memory and loaded into main memory when they are running.

 Disk drives

 Hard disk drive , floppy disk drive, USB drive

 Optical drives

Input Devices

 Input is any data the computer collects

from the outside world.

 The device that collects the data and

sends it to the computer is called an

input device

 Keyboard, mouse, scanner, digital

camera, …

 Disk drives and optical drives can be

considered input devices

Output Devices

to the outside world.

printers.

be considered output devices.

run on a computer

 Operating system: is a set of programs

that manages the hardware and control

their processes

 Application software: refers to programs that make the computer useful to the user such as word processing, spreadsheet,

database packages, …

4 Programming Languages

What Is a Program?

 A program is a set of instructions a

computer follows in order to perform a task.

language used to write computer

programs

What Is a Program?

 Suppose we want the computer to

calculate someone’s gross pay.

 The following is a list of things the

computer should do to perform the task:

 1 Display a message on the screen: “How

many hours did you work?”

 2 Allow user to enter the number of hours

worked.

 3 Once the user enters a number, store it in memory.

What Is a Program? (Cont’d)

 4 Display a message on the screen: “How

much do you get paid per hour?”

 5 Allow the user to enter an hourly pay rate.

 6 Once the user enters a number, store it in memory.

 7 Once both the number of hours worked and the hourly pay rate are entered, multiply the two numbers and store the result in memory.

 8 Display a message on the screen that

shows the amount of money earned.

What Is a Program? (Cont’d)

What Is a Program? (Cont’d)

(numbers).

words instead of number, were

invented to ease the task of

programming.

What Is a Program? (Cont’d)

A History of Java

Sun Microsystems It was named the Green Team.

hand-held device named *7 that could

be used to control a variety of home

entertainment devices.

 It had to use a programming language that

A History of Java (Cont’d)

engineer, created a programming

language, which was named Oak

Then, it was renamed Java.

browser HotJava:

 was able to download and run small Java programs known as applets

Java Application and Applets

may be created with Java:

 Application: is a stand-alone program that runs on your computer

 Applet: is designed to be transmitted over the Internet from a Web server, and then executed in a Web browser

5 What Is a Program Made

of?

common to all programming

languages.

Language Elements

Programmer-Defined Names, Syntax

Language Elements

 Key Words (Reserved Words) (Table 1-3)

 Have a special meaning

 Used for their intended purpose only

 Operators

 Are symbols or words that perform operator

on one or more oparands.

Language Elements (Cont’d)

 Defined by the programmer

 Used to identify storage locations in

memory and parts of the program

 Usually called identifiers

 Rules that be followed when writing a

program

Language Elements (Cont’d)

1 public class Payroll

8 grossPay = hours * payRate ;

9 System out println (“Your gross pay is $” + grossPay );

10 }

11 }

Lines and Statements

 A program contains lines of codes

 Some lines are empty → to make a

program more readable

 Variables are used to store an item of

data in memory.

 A variable is a named storage location in

the computer’s memory.

 Variables are symbolic names made up

by programmer that represent locations

in the computer’s memory.

 hours, grossPay, payRate are

variables

The Compiler and the Java

Virtual Machine

computer and saved to a file using a text editor

 A Java programming statements written by the programmer are called source code

 The file is called a source file, and the

filename ends with the .java extension,

e.g Payroll.java

The Compiler and the Java

Virtual Machine (Cont’d)

source code into an executable form.

 Syntax errors are mistakes that the

programmer has made that violate the

rules of the programming languages

 These errors must be corrected before the compiler can translate the source code

The Compiler and the Java

Virtual Machine (Cont’d)

(e.g C/C++ compilers) translate

source code directly into files that

contains machine language

instructions These files are called

executable files.

The Compiler and the Java

Virtual Machine (Cont’d)

 The Java compiler translates a Java

source file into a file (a byte code file)

that contains byte code instructions

 Byte code filename ends with .class extension.

 Byte code instructions are not machine

language, and cannot be directly

executed by the CPU.

 To execute the byte code file, we use the

Java Virtual Machine (JVM).

The Compiler and the Java

Virtual Machine (Cont’d)

and executes them.

 JVM is often called an interpreter, and Java

is often referred to as an interpreted

language

Program Development Process

 Portable : A program may be written

on one type of computer and then run

on a wide variety of computers, with little or no modification necessary.

computers: highly portable

computer that has a Java Virtual

Portability (Cont’d)

Java byte code may be run on any

computer with Java Virtual Machine.

Java Software Editions

Java programs is referred to as the

 Java SE ̶̶ The Java Standard Edition

provides all the essential software tools

necessary for writing Java applications and applets

Java Software Editions

(Cont’d)

 Java EE ̶̶ The Java Enterprise Edition

provides tools for creating large business applications that employ servers and

provide services over the Web

 Java ME ̶̶ The Java Micro Edition provides

a small, highly optimized runtime

environment for consumer products such

as cell phones, pagers, and appliances

Compiling and Running a Java Program

 Download Java SE 6 Update RC 10 at

http://java.sun.com/javase/downloads/index.j sp

 For Windows Platform, download this file

http://www.java.net/download/jdk6/6u1 0/promoted/b32/binaries/jdk-6u10-rc2- bin-b32-windows-i586-p-

12_sep_2008.exe

Compiling and Running a Java Program (Cont’d)

 Run 12_sep_2008.exe

jdk-6u10-rc2-bin-b32-windows-i586-p-Compiling and Running a Java Program (Cont’d)

Payroll.java in the folder

Compiling and Running a Java Program (Cont’d)

Compiling and Running a Java Program (Cont’d)

 Run the file java.exe

java ClassFilename (class filename

without extension .class)

java Payroll

Integrated Development

Environments

 Java integrated development

environments (IDEs) consist of

Integrated Development

Environments (Cont’d)

 Unzip and run Eclipse.exe

 Create a new Java project:

 File New Java Project

 Enter the project name

 Choose some options

 Finish

 Create a new class

 File New Class

 Enter the class name

 Choosing some options

 Finish

6 Programming Process

 The programming Process consists of

several steps, which include design,

creation, test, and debugging activities.

 The following steps help you in writing

programs

 1 Clearly define what the program is to do

 2 Visualize the program running on the

computer

6 Programming Process

(Cont’d)

 3 Use design tools to create a model of

the program

 4 Check the model for logical errors

 5 Enter the code and compile it

 6 Correct any errors found during

compilation Repeat Steps 5 and 6 as many times as necessary

 7 Run the program with test data for

input

6 Programming Process

(Cont’d)

 8 Correct any running errors found while running the program Repeat Steps 5 to 8

as many times as necessary

 9 Validate the results of the program

Calculate the user’s gross pay

 1 Clearly define what the program is to

do

 Purpose To calculate the user’s gross pay

 Input Number of hours worked,

hourly pay rate

 Process Multiply number of hours

worked by hourly pay rate

The result is the gross pay.

 Output Display a message indicating

the user’s gross pay.

Calculate the user’s gross pay (Cont’d)

the computer

 First create it in your mind

 Imagine what the computer screen will

look like while the program is running

Calculate the user’s gross pay (Cont’d)

 3 Use design tools to create a model of

the program

 Use one or more design tools to create a

model of the program

 For example, pseudocode

 is a cross between human language and a programming language

 is helpful when designing an algorithm

 Looks more like commands than English statements

Calculate the user’s gross pay (Cont’d)

 Pseudocode describes the pay-calculating algorithm

 Get payroll data

 Calculate gross pay

 Display gross pay

Calculate the user’s gross pay (Cont’d)

 A more detailed pseudocode

 Display “How many hours did you work?”.

 Display the value in the pay variable

Calculate the user’s gross pay (Cont’d)

 Logical errors mistakes that cause the

program to produce erroneous results

 Once a model of the program is

assembled, it should be checked for these errors

 If pseudocode is used, the programmer

should trace through it, checking the logic

Calculate the user’s gross pay (Cont’d)

 5 Enter the code and compile it

 Once a model of the program has been

created, checked, and corrected, the

programmer is ready to write source code on the computer.

 The programmer saves the source code to a file and begin the process of compiling it.

 During this step the compiler will find any

syntax errors that may exist in the program.

Calculate the user’s gross pay (Cont’d)

compilation Repeat Steps 5 and 6 as many times as necessary.

 If the compiler reports any errors, they

must be corrected Steps 5 and 6 must be repeated until the program is free of

compile-time error

Calculate the user’s gross pay (Cont’d)

input

 Run-time error is an error that occurs while the program is running These are usually logical errors

 Testing for run-time errors requires that

the program must be executed with

samples data or sample input

Calculate the user’s gross pay (Cont’d)

 8 Correct any running errors found while running the program Repeat Steps 5 to 8

as many times as necessary

 When runtime-errors are found in a program, they must be corrected.

 9 Validate the results of the program

 Enter test data and determine if the program solves the original problem.

7 Object-Oriented

Programming

 Java is an object-oriented programming

(OOP) language OOP is a method of

software development that has its own practices, concepts, and vocabulary.

 There are two primarily methods of

programming in use today:

 Procedural

 Object-oriented

7 Object-Oriented

Programming (Cont’d)

 Procedural Approach

 Procedure is a set of programming statements that,

together, perform a task.

 Procedures typically operate on data items that separate from the procedure.

 In a procedural program, data items are commonly passed from one procedure to another.

 The focus of procedural programming is on the creation of procedures that operate on the program’s data.

 The separation of data and the code that operates on the data often leads to problems

7 Object-Oriented

Programming (Cont’d)

 Object-Oriented Approach

 OOP is centered on creating objects.

 An object is a software entity that contains

data and procedures

 Data contained in an object is known as the object’s

7 Object-Oriented

Programming (Cont’d)