Java Environment (CSS444)

1. Java Environment (CSS444) • Introduction • Object Oriented Programming Concepts • Basics for Java Applications • Basics for Java Applets • Control Structures • Methods • Arrays • Object Oriented Programming • Inheritance, Superclasses, Subclasses, Polymorphism, Abstract and concrete classes • Strings and Characters • Exception Handling • Files and Streams • Java Database Connectivity

2. Chapter 1 - Introduction to Computers, the Internet, and the World Wide Web Outline 1.1 Introduction 1.3 Computer Organization 1.4 Evolution of Operating Systems 1.5 Distributed and Client/Server Computing 1.6 Machine Languages, Assembly Languages and High-Level Languages 1.8 History of Java 1.9 Java Class Libraries 1.10 Other High-Level Languages 1.11 Structured Programming 1.13 Basics of a Typical Java Environment 1.14 General Notes about Java and This Book

3. 1.1 Introduction • Java • Powerful, object-oriented language • Fun to use for beginners, appropriate for experienced programmers • Language of choice for Internet and network communications • Free implementation at http://java.sun.com

4. 1.3 Computer Organization • Six logical units in every computer • Input unit • Gets information from input devices (keyboard, mouse) • Output unit • Gets information (to screen, to printer, to control other devices) • Memory unit • Rapid access, low capacity, stores input information • Arithmetic and logic unit (ALU) • Performs arithmetic calculations and logic decisions • Central processing unit (CPU) • Supervises and coordinates the other sections of the computer • Secondary storage unit • Cheap, long-term, high-capacity storage, stores inactive programs and data

5. 1.4 Evolution of Operating Systems • Batch processing • Doonly one job or task at a time • Operating systems • Manage transitions between jobs • Increased throughput - amount of work computers process • Multiprogramming • Many jobs or tasks sharing the computer resources • Timesharing • Runs a small portion of one user’s job then moves on to service the next user • Programs appear to be running simultaneously

6. 1.5 Distributed and Client/Server Computing • Distributed computing • Organization has a Local Area Network (LAN) • Computers linked to it • Computing distributed over the LAN, rather than at one central location

7. 1.5 Distributed and Client/Server Computing • Client/Server computing • File servers offer common store of programs that client computers access • C and C++ popular for writing operating systems, networking, and distributed client/server applications • Java used for Internet-based applications

8. 1.6 Machine Languages, Assembly Languages and High-Level Languages • Types of programming languages • Machine languages • Strings of numbers giving machine specific instructions • Example: +1300042774+1400593419+1200274027 • Assembly languages • English-like abbreviations representing elementary computer operations (translated via assemblers) • Example: LOAD BASEPAY ADD OVERPAY STORE GROSSPAY

9. 1.6 Machine Languages, Assembly Languages and High-Level Languages • Types of programming languages 3. High-level languages • Similar to everyday English and use mathematical notations (translated via compilers) • Example: grossPay = basePay + overTimePay

10. 1.8 History of Java • Java • Based on C and C++ • Originally developed in early 1991 for intelligent consumer electronic devices • Market did not develop, project in danger of being cancelled • Internet exploded in 1993, saved project • Used Java to create web pages with dynamic content • Java formally announced in 1995 • Now used to create web pages with interactive content, enhance web servers, applications for consumer devices (pagers, cell phones)...

11. 1.9 Java Class Libraries • Java programs • Consist of pieces called classes • Classes contain methods, which perform tasks • Class libraries • Also known as Java API (Applications Programming Interface) • Rich collection of predefined classes, which you can use • Two parts to learning Java • Learning the language itself, so you can create your own classes • Learning how to use the existing classes in the libraries

12. 1.10 Other High-Level Languages • A few other high-level languages have achieved broad acceptance • FORTRAN (FORmula TRANslator) • Scientific and engineering applications • COBOL (COmmon Business Oriented Language) • Used to manipulate large amounts of data • Pascal • Intended for academic use • BASIC • Developed in 1965 as a simple language to help novices

13. 1.11 Structured Programming • Structured programming • Disciplined approach to writing programs • Clear, easy to test and debug, and easy to modify • Pascal designed to teach structured programming in universities • Not used in industrial or commercial applications • Multitasking • Specifying that many activities run in parallel • C and C++ only allow one activity to be performed at a time • Java allows multithreading, where activities can occur in parallel

14. 1.13 Basics of a Typical Java Environment • Java Systems • Consist of environment, language, Java Applications Programming Interface (API), Class libraries • Java programs have five phases • Edit • Use an editor to type Java program • vi or emacs, notepad, Jbuilder, Visual J++ • .java extension • Compile • Translates program into bytecodes, understood by Java interpreter • javac command: javac myProgram.java • Creates .class file, containing bytecodes (myProgram.class)

15. 1.13 Basics of a Typical Java Environment • Java programs have five phases (continued) • Loading • Class loader transfers .class file into memory • Applications - run on user's machine • Applets - loaded into Web browser, temporary • Classes loaded and executed by interpreter with java command java Welcome • HTML documents can refer to Java Applets, which are loaded into web browsers. To load, appletviewer Welcome.html • appletviewer is a minimal browser, can only interpret applets

16. 1.13 Basics of a Typical Java Environment • Java programs have five phases (continued) • Verify • Bytecode verifier makes sure bytecodes are valid and do not violate security • Java must be secure - Java programs transferred over networks, possible to damage files (viruses) • Execute • Computer interprets program one bytecode at a time • Performs actions specified in program • Program may not work on first try • Make changes in edit phase and repeat

17. Disk Disk Interpreter Compiler Editor Bytecode Verifier Class Loader . . . . . . . . . . . . . . . . . . Program is created in the editor and stored on disk. Phase 1 Compiler creates bytecodes and stores them on disk. Phase 2 Primary Memory Phase 3 Class loader puts bytecodes in memory. Disk Primary Memory Phase 4 Bytecode verifier confirms that all bytecodes are valid and do not violate Java’s security restrictions. Primary Memory Interpreter reads bytecodes and translates them into a language that the computer can understand, possibly storing data values as the program executes. Phase 5

18. 1.14 General Notes about Java and This Book • Java • Powerful language • Programming notes • Clarity - Keep it Simple • Portability - Java very portable, but it is an elusive goal • Performance • Interpreted programs run slower than compiled ones • Compiling has delayed execution, interpreting executes immediately • Can compile Java programs into machine code • Runs faster, comparable to C / C++

19. 1.14 General Notes about Java and This Book • Just-in-time compiler • Midway between compiling and interpreting • As interpreter runs, compiles code and executes the program in the machine language rather than reinterpreting. • Not as efficient as full compilers • A full compiler is being developed for Java • Integrated Development Environment (IDE) • Tools to support software development • Several Java IDE's are as powerful as C / C++ IDE's NEXT: * Object-Oriented Programming Concepts