1 Programming Fundamentals AITI-GP

2 Introduction to Programming

3 The Programming Process Create/Edit Program Compile Program Execute Program Compile Errors?Run-Time Errors? Source Program Object Program

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 zero step 2. while there is a number to read, repeat steps 2a and 2b: step 2a. read in the number step 2b. add number to total step 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 Applet File: 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 My First 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.out object println()

29 HelloAgain Applet: Creation USERBROWSER HelloAgain Applet g: Graphics object 1: Open HA.html 2: new 3: paint() 4: drawString() Note: new means the object of class HelloAgain is created

30 HelloAgain Applet: Another Scenario USERBROWSER HelloAgain Applet g: Graphics object 1: Move the browser window 2: paint() 3: drawString()