INF120 Basics in JAVA Programming AUBG, COS dept Lecture 01 Title: Computers, SDM, Algorithms,...

INF120 Basics in JAVA ProgrammingAUBG, COS dept

Lecture 01Title:

Computers, SDM, Algorithms,

Programs and Java

Malik Ch 1, Farrell Ch 1, Liang Ch 1

Lecture Contents:

• Computers• Software Development Method• Algorithms• Programs• Java Prog Lan

What is a Computer?

“A device for counting or computing “

A computer consists of a CPU, memory, hard disk, CD drive, monitor, printer, and communication devices.

e.g., Disk, CD, and Tape

Input Devices

e.g., Keyboard, Mouse

e.g., Monitor, Printer

Communication Devices

e.g., Modem, and NIC

Storage Devices

Memory

Output Devices

CPUThe central processing unit (CPU) is the brain of a computer. It retrieves instructions from memory and executes them. The CPU speed is measured in megahertz (MHz), with 1 megahertz equaling 1 million pulses per second. The speed of the CPU has been improved continuously. If you buy a PC now, you can get an Intel Pentium 4 Processor at 3 gigahertz (1 gigahertz is 1000 megahertz).

Input Devices

Storage Devices

Memory

Output Devices

MemoryMemory is to store data and program instructions for CPU to execute. A memory unit is an ordered sequence of bytes, each holds eight bits. A program and its data must be brought to memory before they can be executed. A memory byte is never empty, but its initial content may be meaningless to your program. The current content of a memory byte is lost whenever new information is placed in it.

Input Devices

Storage Devices

Memory

Output Devices

How Data is Stored?Data of various kinds, such as numbers, characters, and strings, are encoded as a series of bits (zeros and ones). Computers use zeros and ones because digital devices have two stable states, which are referred to as zero and one by convention. The programmers need not to be concerned about the encoding and decoding of data, which is performed automatically by the system based on the encoding scheme. The encoding scheme varies. For example, character ‘J’ is represented by 01001010 in one byte. A small number such as three can be stored in a single byte. If computer needs to store a large number that cannot fit into a single byte, it uses a number of adjacent bytes. No two data can share or split a same byte. A byte is the minimum storage unit.

01001010

01100001

01110110

01100001

00000011

Memory content

Memory address

Encoding for character ‘J’ Encoding for character ‘a’ Encoding for character ‘v’ Encoding for character ‘a’ Encoding for number 3

7Java Programming: From Problem Analysis to Program Design, 4e

Language of a Computer (continued)

Storage DevicesMemory is volatile, because information is lost when the power is off. Programs and data are permanently stored on storage devices and are moved to memory when the computer actually uses them. There are three main types of storage devices:Disk drives (hard disks and floppy disks), CD drives (CD-R and CD-RW), and Tape drives.

Input Devices

Storage Devices

Memory

Output Devices

Output Devices: MonitorThe monitor displays information (text and graphics). The resolution and dot pitch determine the quality of the display.

Input Devices

Storage Devices

Memory

Output Devices

Monitor Resolution and Dot PitchThe screen resolution specifies the number of pixels in horizontal and vertical dimensions of the display device. Pixels (short for “picture elements”) are tiny dots that form an image on the screen. A common resolution for a 17-inch screen, for example, is 1,024 pixels wide and 768 pixels high. The resolution can be set manually. The higher the resolution, the sharper and clearer the image is.

resolution

The dot pitch is the amount of space between pixels, measured in millimeters. The smaller the dot pitch, the sharper the display.

dot pitch

Communication DevicesA regular modem uses a phone line and can transfer data in a speed up to 56,000 bps (bits per second). A DSL (digital subscriber line) also uses a phone line and can transfer data in a speed 20 times faster than a regular modem. A cable modem uses the TV cable line maintained by the cable company. A cable modem is as fast as a DSL. Network interface card (NIC) is a device to connect a computer to a local area network (LAN). The LAN is commonly used in business, universities, and government organizations. A typical type of NIC, called 10BaseT, can transfer data at 10 mbps (million bits per second).

Input Devices

Storage Devices

Memory

Output Devices

Programs

Computer programs, known as software, are instructions to the computer.

You tell a computer what to do through programs. Without programs, a computer is an empty machine, known as hardware.

Computers do not understand human languages, so you need to use computer languages to communicate with them.

Programs are written using programming languages.

Programming LanguagesMachine Language Assembly Language High-Level Language

Machine language is a set of primitive instructions built into every computer. The instructions are in the form of binary code, so you have to enter binary codes for various instructions. Program with native machine language is a tedious process. Moreover the programs are highly difficult to read and modify. For example, to add two numbers, you might write an instruction in binary like this:

1101101010011010

Assembly languages were developed to make programming easy. Since the computer cannot understand assembly language, however, a program called assembler is used to convert assembly language programs into machine code. For example, to add two numbers, you might write an instruction in assembly code like this: ADDF3 R1, R2, R3

… ADDF3 R1, R2, R3 …

Assembly Source File

Assembler

… 1101101010011010 …

Machine Code File

The high-level languages are English-like and easy to learn and program. For example, the following is a high-level language statement that computes the area of a circle with radius 5:

area = 5 * 5 * 3.1415;

Popular High-Level Languages

Language Description

FORTRAN

Pascal

Python

Visual Basic

Named for Ada Lovelace, who worked on mechanical general-purpose computers. The Ada language was developed for the Department of Defense and is used mainly in defense projects.

Beginner’s All-purpose Symbolic Instruction Code. It was designed to be learned and used easily by beginners.

Developed at Bell Laboratories. C combines the power of an assembly language with the ease of use and portability of a high-level language.

C++ is an object-oriented language, based on C.

Pronounced “C Sharp.” It is a hybrid of Java and C++ and was developed by Microsoft.

COmmon Business Oriented Language. Used for business applications.

FORmula TRANslation. Popular for scientific and mathematical applications.

Developed by Sun Microsystems, now part of Oracle. It is widely used for developing platform-independent Internet applications.

Named for Blaise Pascal, who pioneered calculating machines in the seventeenth century. It is a simple, structured, general-purpose language primarily for teaching programming.

A simple general-purpose scripting language good for writing short programs.

Visual Basic was developed by Microsoft and it enables the programmers to rapidly develop graphical user interfaces.

Interpreting/Compiling Source Code

A program written in a high-level language is called a source program or source code. Because a computer cannot understand a source program, a source program must be translated into machine code for execution. The translation can be done using another programming tool called an interpreter or a compiler.

Interpreting Source CodeAn interpreter reads one statement from the source code, translates it to the machine code or virtual machine code, and then executes it right away, as shown in the following figure. Note that a statement from the source code may be translated into several machine instructions.

… area = 5 * 5 * 3.1415; ...

High-level Source File

Interpreter Output

Compiling Source CodeA compiler translates the entire source code into a machine-code file, and the machine-code file is then executed, as shown in the following figure.

… area = 5 * 5 * 3.1415; ...

High-level Source File

Compiler Executor Output …

0101100011011100 1111100011000100 … ...

Machine-code File

Operating SystemsThe operating system (OS) is a program that manages and controls a computer’s activities. The popular operating systems for general-purpose computers are Microsoft Windows, Mac OS, and Linux. Application programs, such as a Web browser or a word processor, cannot run unless an operating system is installed and running on the computer.

Application Programs

Operating System

Hardware

Problem Solving Process

• Developing SW (computer programs) is not only a pure programming activity.

• Developing SW (computer programs) is a sequence of sequential stages, known as– Problem Solving Process or– SDM– SLC– PDC

Problem-Solving Process

1. Analyze the problem and outline the problem and its solution requirements

2. Design an algorithm to solve the problem3. Implement the algorithm in a programming

language, such as Java4. Verify that the algorithm works5. Maintain the program by using and

improving it and modifying it if the problem domain changes

Problem-Analysis-Coding-Execution Cycle

Software Development Process Requirement Specification

System Analysis

System Design

Testing

Implementation

Maintenance

Deployment

Requirement Specification Requirement Specification

System Analysis

System Design

Testing

Implementation

Maintenance

Deployment

A formal process that seeks to understand the problem and document in detail what the software system needs to do. This phase involves close interaction between

users and designers.

Most of the examples in this book are simple, and their requirements are clearly stated. In the real world, however, problems are not well defined. You need to study a problem carefully to identify its requirements.

System AnalysisRequirement Specification

System Analysis

System Design

Testing

Implementation

Maintenance

Deployment

Seeks to analyze the business process in terms of data flow, and to identify the system’s input and output.

Part of the analysis entails modeling the system’s behavior. The model is intended to capture the essential elements of the system and to define services to the system.

System Design Requirement Specification

System Analysis

System Design

Testing

Implementation

Maintenance

Deployment

The process of designing the system’s components.

This phase involves the use of many levels of abstraction to decompose the problem into manageable components, identify classes and interfaces, and establish relationships among the classes and interfaces.

IPO Requirement Specification

System Analysis

System Design

Input, Process, Output

Testing

Implementation

Maintenance

Deployment The essence of system analysis and design is input, process, and output. This is called IPO.

Implementation Requirement Specification

System Analysis

System Design

Testing

Implementation

Maintenance

Deployment

The process of translating the system design into programs. Separate programs are written for each component and put to work together.

This phase requires the use of a programming language like Java. The implementation involves coding, testing, and debugging.

Testing Requirement Specification

System Analysis

System Design

Testing

Implementation

Maintenance

Deployment

Ensures that the code meets the requirements specification and weeds out bugs.

An independent team of software engineers not involved in the design and implementation of the project usually conducts such testing.

Deployment Requirement Specification

System Analysis

System Design

Testing

Implementation

Maintenance

Deployment

Deployment makes the project available for use.

For a Java applet, this means installing it on a Web server; for a Java application, installing it on the client's computer.

Maintenance Requirement Specification

System Analysis

System Design

Testing

Implementation

Maintenance

Deployment

Maintenance is concerned with changing and improving the product.

A software product must continue to perform and improve in a changing environment. This requires periodic upgrades of the product to fix newly discovered bugs and incorporate changes.

Programming Methodologies

• Two basic approaches to programming design

–Structured Design

–Object-Oriented Design

Structured Design

1. A problem is divided into smaller subproblems

2. Each subproblem is solved

3. The solutions of all subproblems are then combined to solve the problem

Object-Oriented Design (OOD)

• In OOD, a program is a collection of interacting objects

• An object consists of data and operations

• Steps in OOD1. Identify objects

2. Form the basis of the solution

3. Determine how these objects interact

Java Programming, Fifth Edition 36

Understanding Objects and Classes• Objects

– Made up of attributes and methods

• Attributes– Characteristics that define object– Differentiate objects of same class– Value of attributes is object’s state

• Class – Describes objects with common properties– Definition– Instance

Understanding Objects and Classes

Object-Oriented Design Example 1

• Problem statement– Write a program to input the length and width

of a rectangle, and calculate and print the perimeter and area of the rectangle

• Nouns– Length, width, rectangle, perimeter, area

class Rectangle with 2 Data Members and 7 Operations

Object-Oriented Design Example 2

• An inoperable candy machine has a cash register and four dispensers to hold and release items sold by the machine

• The machine sells: candies, chips, gum, and cookies

• Write a program for this candy machine so that it can be put into operation

Object-Oriented Design Example 2 (continued)

Algorithms

• Computer programs implement algorithms.

• So, what is an algorithm?

Algorithms definitionsDefinition 1: A step-by-step problem-solving process in

which a solution is arrived at in a finite amount of time

Definition 2:A procedure for solving a problem in terms of1. the actions to be executed, and2. the order in which these actions are to be executedis called an algorithm.

Definition 3:An algorithm is a list of steps for solving a problem.

Classification of algorithms:

• Linear or Sequence algorithms;

• Branch algorithms;

• Loop algorithms.

Design NotationsThree “notations” used to document algorithms:

• Flowchartalso called control-flow diagram

• Pseudo codeUses English-like phrases with some Java terms to outline the program

• Hierarchy chartShow how the different parts of a program relate to each other

Problem: Converting Miles to Kilometers

Describe the algorithm

Converting miles to kilometers

Converting Miles to Kilometers:flowchart /control-flow diagram/

Converting Miles to Kilometers:using pseudo code

Converting miles to kilometers

1. Read the number of miles

2. Set the number of kilometers to 1.609 * miles

3. Display the number of kilometers

Converting Miles to Kilometers:using hierarchy chart

Source text in Java// MilesToKms.java// Algorithm converting distance in miles to kilometers

import java.util.*;

public class MilesToKms {

public static void main(String[] args) { Scanner ptinp = new Scanner(System.in); double miles; // input double kms; // output

// step 1 - get the distance (input) System.out.print("Enter distance in miles:"); miles = Double.parseDouble( ptinp.next() ); // step 2 - convert the distance from miles to kilometers kms = 1.609 * miles; // step 3 - display the distance in kilometers (output) System.out.println("\n That equals " + kms + " kilometers"); }}

Classification of algorithms:

• Linear or Sequence algorithms;

• Branch algorithms;

• Loop algorithms.

Why Java?

The answer is that Java enables users to develop and deploy applications on the Internet for servers, desktop computers, and small hand-held devices. The future of computing is being profoundly influenced by the Internet, and Java promises to remain a big part of that future. Java is the Internet programming language.

Java is a general purpose programming language. Java is the Internet programming language.

Java Program Types

• Java Applets– Programs embedded in Web page

• Java Applications, called also Java stand-alone programs– Console applications

• Support character output to a computer screen in a DOS window

– Windowed applications that create GUI with elements like• Menus

• Toolbars

• Dialog boxes

Java, Web, and Beyond

Java can be used to develop Web applications.

Java Applets Java Web Applications Java can also be used to develop applications

for hand-held devices such as Palm and cell phones

Examples of Java’s Versatility (Applets)

PDA and Cell Phone

Java’s History James Gosling and Sun Microsystems

Java, May 20, 1995, Sun World

HotJava – The first Java-enabled Web browser

Early History Website:

http://www.java.com/en/javahistory/index.jsp

Characteristics of Java Java Is Simple Java Is Object-Oriented Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable Java's Performance Java Is Multithreaded Java Is Dynamic

www.cs.armstrong.edu/liang/JavaCharacteristics.pdf

JDK Versions JDK 1.02 (1995) JDK 1.1 (1996) JDK 1.2 (1998) JDK 1.3 (2000) JDK 1.4 (2002) JDK 1.5 (2004) a. k. a. JDK 5 or Java 5 JDK 1.6 (2006) a. k. a. JDK 6 or Java 6 JDK 1.7 (2011) a. k. a. JDK 7 or Java 7

JDK Editions Java Standard Edition (J2SE)

– J2SE can be used to develop client-side standalone applications or applets.

Java Enterprise Edition (J2EE)– J2EE can be used to develop server-side applications such

as Java servlets, Java ServerPages, and Java ServerFaces. Java Micro Edition (J2ME).

– J2ME can be used to develop applications for mobile devices such as cell phones.

This book uses J2SE to introduce Java programming. Popular Java IDEs: NetBeans, Eclipse

Two More Simple Examples

RunRunWelcomeWithThreeMessagesWelcomeWithThreeMessages

RunRunComputeExpressionComputeExpression

Programming Errors

Syntax Errors– Detected by the compiler

Runtime Errors– Causes the program to abort

Logic Errors– Produces incorrect result

Syntax Errorspublic class ShowSyntaxErrors { public static main(String[] args) { System.out.println("Welcome to Java); }}

Runtime Errors

public class ShowRuntimeErrors { public static void main(String[] args) { System.out.println(1 / 0); }}

Logic Errors

public class ShowLogicErrors { public static void main(String[] args) { System.out.println("Celsius 35 is Fahrenheit degree "); System.out.println((9 / 5) * 35 + 32); }}

DebuggingLogic errors are called bugs. The process of finding and correcting errors is called debugging. A common approach to debugging is to use a combination of methods to narrow down to the part of the program where the bug is located. You can hand-trace the program (i.e., catch errors by reading the program), or you can insert print statements in order to show the values of the variables or the execution flow of the program. This approach might work for a short, simple program. But for a large, complex program, the most effective approach for debugging is to use a debugger utility.

Debugger

Debugger is a program that facilitates debugging. You can use a debugger to

Execute a single statement at a time.Trace into or stepping over a method.Set breakpoints.Display variables.Display call stack.Modify variables.

Thank You For

Your Attention!

Any Questions?

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