1. CS 3131 Introduction to Programming in Java Rich Maclin Computer Science Department

2. 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)

3. 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)

4. Chapter 1 Overview of programming languages –compilers –interpreters Origin of Java Application versus Applet Object-Oriented Programming –classes –inheritance

5. Computer Languages Machine language –01010110 ADD R1,R2 Assembly language –ADD R1,R2 High-level programming language –X+Y

6. 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

7. Object Code Compilers generally produce machine code Some produce intermediate code Intermediate code executed by interpreter Java compiles to byte-code Byte-code interpreted

8. 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

9. 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)

10. 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)

11. 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

12. The Internet Originated by defense department Mechanism of decentralized communication Nodes route communication to others (seamlessly)

13. 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

14. HyperText Markup Language (HTML) Language used in web documents Contains commands enclosed in <> – bold for bold text Commands interpreted by machine Can contain references to Java programs – code = “Name.class”

15. Page Title Title on the Page code = “Name.class” width = 100 height = 100

16. Java Programs Applications –stand alone –compiled, run with interpreter Applets –not intended to run on its own –embedded in web page

17. Application public class HelloWorld { // A simple application public static void main (String argv[]) { System.out.println(“Hello world!”); } produces output: Hello world!

18. 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

19. 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

20. 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)

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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); }