Transcript Notes, Part I

Programming Fundamentals
AITI-GP
1
Introduction to Programming
2
The Programming Process
Compile Errors?
Create/Edit
Program
Source
Program
Compile
Program
Run-Time Errors?
Object
Program
Execute
Program
3
The Software Life Cycle
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Problem Solving Phase
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Implementation Phase (Programming)
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Analyze Problem
Develop Solution (Algorithm construction)
Verify
Implement Algorithm
Test
Maintenance Phase
4
Problem Solving and
Programming
Problem
Algorithm
Program
5
Constructing Algorithms
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Pseudo-code
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English-like
Concise
Not constrained by language rules
Flowchart
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Diagram
Visual objects (rectangles, arrows, etc) to
describe control flow
6
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
7
Introduction to Java
8
Computing in the 1990s
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The Internet and the WWW
Graphical User Interfaces (GUIs)
Object-oriented Programming (OOP)
9
The Internet
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A global network of computers
The World Wide Web (WWW)
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users retrieve documents
remote programs may be invoked
Need language platforms that are:
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network-aware
portable
secure
10
Graphical User Interfaces
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Users interact with an application
through visual objects:
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Mouse and pointer facilitate certain
actions:
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Windows, Buttons, Text fields, etc.
click, drag, drop, etc.
“Visual Programming”
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focus is on handling UI objects and events
11
Object-Oriented Programming
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Program (revised definition):
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Object:
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collection of interacting objects
a thing that has identity, state, and
behavior
instance of a class
OOP:
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focus is on developing classes that specify
state (variables) and behavior (functions)12
Enter Java
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1991
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1993
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Sun Microsystems develops a language
(based on C) for consumer electronic
devices
WWW explodes in popularity
increased need for “dynamic” Web pages
1995
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Sun formally announces Java for web use13
What is Java?
Java is a general purpose programming
language that is:
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object-oriented
interpreted, architecture-neutral, portable
distributed (network-aware), secure
simple, robust
multi-threaded
high-performance (?)
14
Two Types of Java Programs
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Applications
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general-purpose programs
standalone
executed through the operating system
Applets
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programs meant for the WWW
embedded in a Web page
normally executed through a browser
15
Simple Java Application
File: Hello.java
// Hello World application
public class Hello {
public static void main(String args[])
{
System.out.println(“Hello world”);
}
}
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Compilation and Execution

Compile using javac (compiler)
C> javac Hello.java
 Hello.class file is produced
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Execute using java (interpreter)
C>java Hello
 requires a Hello.class file
17
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);
}
}
18
Executing Applets
After compiling the java program:
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Embed an “applet tag” in an .html
document that references the .class file
Open the .html document using a
browser or the appletviewer
19
Sample .html Document
File: HA.html
<h1> My First Applet </h1>
<applet code=“HelloAgain.class” height=200
width=100>
</applet>
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What is HTML?
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Hypertext Markup Language
Underlying language of Web pages
A means of providing formatting
instructions for presenting content
Text-based
.html documents:
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collection of content and controls (tags)
21
Java Program Structure
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Java Program
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(optional) import declarations
class declaration
Class
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class name should match its file name
may extend an existing class (such as
Applet)
contains method/function declarations
22
Lab Exercises
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Create, compile, and execute the
sample Java application and applet
23
Event-Driven Programming
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Programming User Interface events
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e.g., what happens when you click on a
button
Example: TFCopy1 Applet
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two text fields and a button
clicking on the button causes the contents
of a text field to be transferred to the other
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Object Interaction in Java
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Programming Paradigms
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Procedural Programming (C)
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focus is on writing procedures/functions
program execution viewed as functions
calling other functions
Object-oriented Programming (Java)
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focus is on writing classes for objects
program execution viewed as objects
interacting with each other
26
OOP and Object Interaction
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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
27
Hello.java Application
println()
System.out
object
28
HelloAgain Applet: Creation
USER
1: Open HA.html
BROWSER
2: new
3: paint()
g: Graphics
object
4: drawString()
HelloAgain
Applet
Note: new means the object of class HelloAgain is created
29
HelloAgain Applet:
Another Scenario
USER
BROWSER
1: Move the
browser window
2: paint()
g: Graphics
object
3: drawString()
HelloAgain
Applet
30