1 programming fundamentals aiti-gp. 2 introduction to programming

1

Programming Fundamentals

AITI-GP

2

Introduction to Programming

3

The Programming Process

Create/EditProgram

CompileProgram

ExecuteProgram

Compile Errors? Run-Time Errors?

SourceProgram

ObjectProgram

4

The Software Life Cycle Problem Solving Phase

Analyze Problem Develop Solution (Algorithm construction) Verify

Implementation Phase (Programming) Implement Algorithm Test

Maintenance Phase

5

Problem Solving and Programming

Problem Algorithm Program

6

Constructing Algorithms Pseudo-code

English-like Concise Not constrained by language rules

Flowchart Diagram Visual objects (rectangles, arrows,

etc) to describe control flow

7

Algorithm Example (Pseudocode)

Computing a total

step 1. initialize total to zerostep 2. while there is a number to

read, repeat steps 2a and 2b: step 2a. read in the number step 2b. add number to totalstep 3. print out total

8

Introduction to Java

9

Computing in the 1990s

The Internet and the WWW Graphical User Interfaces (GUIs) Object-oriented Programming

(OOP)

10

The Internet A global network of computers The World Wide Web (WWW)

users retrieve documents remote programs may be invoked

Need language platforms that are: network-aware portable secure

11

Graphical User Interfaces Users interact with an application

through visual objects: Windows, Buttons, Text fields, etc.

Mouse and pointer facilitate certain actions: click, drag, drop, etc.

“Visual Programming” focus is on handling UI objects and events

12

Object-Oriented Programming Program (revised definition):

collection of interacting objects Object:

a thing that has identity, state, and behavior instance of a class

OOP: focus is on developing classes that specify

state (variables) and behavior (functions)

13

Enter Java 1991

Sun Microsystems develops a language (based on C) for consumer electronic devices

1993 WWW explodes in popularity increased need for “dynamic” Web pages

1995 Sun formally announces Java for web use

14

What is Java?

Java is a general purpose programming language that is: object-oriented interpreted, architecture-neutral,

portable distributed (network-aware), secure simple, robust multi-threaded high-performance (?)

15

Two Types of Java Programs Applications

general-purpose programs standalone executed through the operating system

Applets programs meant for the WWW embedded in a Web page normally executed through a browser

16

Simple Java Application

File: Hello.java

// Hello World application

public class Hello {

public static void main(String args[]) {

System.out.println(“Hello world”);

}

}

17

Compilation and Execution

Compile using javac (compiler)C> javac Hello.java Hello.class file is produced

Execute using java (interpreter)C>java Hello requires a Hello.class file

18

Simple Java AppletFile: HelloAgain.java

import java.awt.*;

import java.applet.Applet;

public class HelloAgain extends Applet {

public void paint(Graphics g) {

g.drawString(“Hello”,50,50);

}

}

19

Executing Applets

After compiling the java program:

Embed an “applet tag” in an .html document that references the .class file

Open the .html document using a browser or the appletviewer

20

Sample .html Document

File: HA.html

<h1> My First Applet </h1><applet code=“HelloAgain.class” height=200

width=100></applet>

21

What is HTML? Hypertext Markup Language Underlying language of Web pages A means of providing formatting

instructions for presenting content Text-based .html documents:

collection of content and controls (tags)

22

Java Program Structure Java Program

(optional) import declarations class declaration

Class class name should match its file name may extend an existing class (such as

Applet) contains method/function declarations

23

Lab Exercises Create, compile, and execute the

sample Java application and applet

24

Event-Driven Programming Programming User Interface events

e.g., what happens when you click on a button

Example: TFCopy1 Applet two text fields and a button clicking on the button causes the

contents of a text field to be transferred to the other

25

Object Interaction in Java

26

Programming Paradigms Procedural Programming (C)

focus is on writing procedures/functions program execution viewed as functions

calling other functions Object-oriented Programming (Java)

focus is on writing classes for objects program execution viewed as objects

interacting with each other

27

OOP and Object Interaction

Objects pass messages to each other An object responds to a message by

executing an associated method defined in its class

Causes a “chain reaction” The user could be viewed as an object Depicted in an Object Interaction

Diagram

28

Hello.java Application

System.outobject

println()

29

HelloAgain Applet: Creation

USER BROWSER

HelloAgainApplet

g: Graphicsobject

1: Open HA.html

2: new3: paint()

4: drawString()

Note: new means the object of class HelloAgain is created

30

HelloAgain Applet:Another Scenario

USER BROWSER

HelloAgainApplet

g: Graphicsobject

1: Move the browser window

2: paint()

3: drawString()