CS 3131 Introduction to Programming in Java

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CS 3131 Introduction to Programming in Java

• Rich Maclin
• Computer Science Department

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Course Overview

• I. Introduction to Java (Ch. 1)
• II. Graphical User Interfaces (GUIs)
• A. Graphics commands (Ch. 2)
• B. Widgets (Ch. 3)
• C. Layouts (Ch. 4)
• III. Java Language Features
• 1. Basic Language Features (Ch.5, part of Ch. 6)

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• III. Java Language Features (cont)
• B. Event Models (Ch. 6)
• 1. 1.0 Model
• 2. 1.1 Model
• C. Building a full program (Ch. 7)
• D. Advanced Language Features (Ch. 8)
• 1. Arrays
• 2. Loops
• E. Exceptions (Ch. 9)
• F. Input/Output Streams (Ch. 10)
• IV. The Next Step (living on the Web)
• A. The World Wide Wait(Web) (Ch. 12)
• B. Threads (Ch. 11)

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Chapter 1

• Overview of programming languages
• compilers
• interpreters
• Origin of Java
• Application versus Applet
• Object-Oriented Programming
• classes
• inheritance

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Computer Languages

• Machine language
• 01010110 ADD R1,R2
• Assembly language
• ADD R1,R2
• High-level programming language
• XY

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Language Translation

• High-level code mapped to low-level code
• Can have multiple steps
• high-level to assembly
• assembly to machine language
• Compiler itself is a program

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Object Code

• Compilers generally produce machine code
• Some produce intermediate code
• Intermediate code executed by interpreter
• Java compiles to byte-code
• Byte-code interpreted

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Advantages of Interpreters

• Different machines can have interpreters specific
  to that machine
• machine independence
• no need for specific compiler for each machine
• code compiled on any machine can be run on any
  with an interpreter

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Disadvantages of Interpreters

• Resulting code slower (10-100 times)
• Still need an interpreter for each machine
• Limited to abilities all machines can produce
  (lose graphics abilities of SGIs)

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Why Java?

• Why not?
• Similar moves had happened before, the difference
  is the World Wide Web
• Java provides a programming tool for web pages
  that
• has graphics capabilities
• is machine independent
• small language (easy to implement)

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Why NOT Java?

• Still very young (undergoing constant change)
• Visual J already dated
• So is our textbook (published in 1998)
• Language is growing in size
• It is slow

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The Internet

• Originated by defense department
• Mechanism of decentralized communication
• Nodes route communication to others (seamlessly)

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World Wide Web

• Based on the internet
• Idea distributed hypermedia
• Pages placed in known locations on machines
  connected to internet
• Browsers can look at those pages
• Pages contain links to other pages/info

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HyperText Markup Language (HTML)

• Language used in web documents
• Contains commands enclosed in ltgt
• ltBgt bold lt/Bgt for bold text
• Commands interpreted by machine
• Can contain references to Java programs
• ltAPPLETgt code Name.class lt/APPLETgt

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ltHTMLgt ltHEADgt ltTITLEgtPage Titlelt/TITLEgt
lt/HEADgt ltBODYgt Title on the Page ltHRgt
ltAPPLETgt code Name.class
width 100 height 100 lt/APPLETgt ltHRgt
lt/BODYgt lt/HTMLgt
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Java Programs

• Applications
• stand alone
• compiled, run with interpreter
• Applets
• not intended to run on its own
• embedded in web page

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Application
public class HelloWorld // A simple
application public static void main (String
argv) System.out.println(Hello
world!) produces output Hello world!
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Applet
import java.applet. import java.awt. public
class HelloWorld extends Applet // A simple
Applet public void paint (Graphics g)
g.drawString(Hello world!,30,30)
Produces output on a web page
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Java files

• ClassName.java - Java source code
• ClassName.class - compiled byte code for
  ClassName.java
• WebPageName.html - web page which may contain
  references to ClassName.class

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Object-Oriented Programming

• Program consists of objects from classes
• A class is a set of objects (instances) with a
  common structure (and purpose)
• Objects consists of
• data values (instance variables)
• methods (class procedures)

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A Robot Class
Robot Data MapLong - number indicating
longitudinal location MapLat - number
indicating latitude location BatteryLevel -
number indicating battery level Methods
MoveForward(x) - move forward x yards
TurnRight(x) - turn right x degrees
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Robot Instances

• Each instance has values for the instance
  variables
• R1 is at long,lat 36.12,38.34
• Each method can be applied to each robot by
  sending that robot a message
• Ask R1 to move forward 5 meters

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Inheritance

• Can define robot class with features all robots
  share
• Then subclasses of robots with specific features
  (e.g., Robots with IR sensors)
• Specific class can inherit the things defining
  regular robots

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Java and Inheritance

• Java relies heavily upon inheritance
• Java provides lots of classes that perform useful
  actions
• Our job is to produce specialized classes to
  perform those aspects we are interested in

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Java packages

• java.applet - basic applet tools
• java.awt - abstract window toolkit (buttons,
  text, etc.)
• java.io - input/output classes
• java.lang - language features
• java.net - classes for working with networks
• java.util - other useful utility classes

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import java.applet. // add classes from applet
pack. import java.awt. // add classes from
awt package public class HelloWorld extends
Applet // New class name HelloWorld //
Class is accessible by all (public) // Class
extends (inherits from) class Applet public
void paint (Graphics g) // Paint is a method
(we are overriding an existing // method)
g.drawString(Hello world!,30,30)