Java: A Powerful and Versatile Programming Language

1. Chapter 1 • Java • Originally for intelligent consumer-electronic devices • Then used for creating Web pages with dynamic content • Now also used for: • Develop large-scale enterprise applications • Enhance WWW server functionality • Provide applications for consumer devices (cell phones, etc.)

2. PDA and Cell Phone

3. Java’s History • James Gosling and Sun Microsystems • Oak • Java, May 20, 1995, Sun World • HotJava • The first Java-enabled Web browser • Early History Website: • http://en.wikipedia.org/wiki/Java_(programming_language) • http://java.sun.com/features/1998/05/birthday.html

4. Characteristics of Java • Java Is Simple • Java Is Object-Oriented • Java Is Distributed • Java Is Interpreted • Java Is Robust • Java Is Secure • Java Is Architecture-Neutral • Java Is Portable • Java's Performance • Java Is Multithreaded • Java Is Dynamic

5. Characteristics of Java Java is partially modeled on C++, but greatly simplified and improved. Some people refer to Java as "C++--" because it is like C++ but with more functionality and fewer negative aspects. • Java Is Simple • Java Is Object-Oriented • Java Is Distributed • Java Is Interpreted • Java Is Robust • Java Is Secure • Java Is Architecture-Neutral • Java Is Portable • Java's Performance • Java Is Multithreaded • Java Is Dynamic

6. Characteristics of Java Java is inherently object-oriented. Although many object-oriented languages began strictly as procedural languages, Java was designed from the start to be object-oriented. Object-oriented programming (OOP) is a popular programming approach that is replacing traditional procedural programming techniques. One of the central issues in software development is how to reuse code. Object-oriented programming provides great flexibility, modularity, clarity, and reusability through encapsulation, inheritance, and polymorphism. • Java Is Simple • Java Is Object-Oriented • Java Is Distributed • Java Is Interpreted • Java Is Robust • Java Is Secure • Java Is Architecture-Neutral • Java Is Portable • Java's Performance • Java Is Multithreaded • Java Is Dynamic

7. Characteristics of Java Distributed computing involves several computers working together on a network. Java is designed to make distributed computing easy. Since networking capability is inherently integrated into Java, writing network programs is like sending and receiving data to and from a file. • Java Is Simple • Java Is Object-Oriented • Java Is Distributed • Java Is Interpreted • Java Is Robust • Java Is Secure • Java Is Architecture-Neutral • Java Is Portable • Java's Performance • Java Is Multithreaded • Java Is Dynamic

8. Characteristics of Java You need an interpreter to run Java programs. The programs are compiled into the Java Virtual Machine code called bytecode. The bytecode is machine-independent and can run on any machine that has a Java interpreter, which is part of the Java Virtual Machine (JVM). • Java Is Simple • Java Is Object-Oriented • Java Is Distributed • Java Is Interpreted • Java Is Robust • Java Is Secure • Java Is Architecture-Neutral • Java Is Portable • Java's Performance • Java Is Multithreaded • Java Is Dynamic

9. Characteristics of Java Java compilers can detect many problems that would first show up at execution time in other languages. Java has eliminated certain types of error-prone programming constructs found in other languages. Java has a runtime exception-handling feature to provide programming support for robustness. • Java Is Simple • Java Is Object-Oriented • Java Is Distributed • Java Is Interpreted • Java Is Robust • Java Is Secure • Java Is Architecture-Neutral • Java Is Portable • Java's Performance • Java Is Multithreaded • Java Is Dynamic

10. Characteristics of Java • Java Is Simple • Java Is Object-Oriented • Java Is Distributed • Java Is Interpreted • Java Is Robust • Java Is Secure • Java Is Architecture-Neutral • Java Is Portable • Java's Performance • Java Is Multithreaded • Java Is Dynamic Java implements several security mechanisms to protect your system against harm caused by stray programs.

11. Characteristics of Java • Java Is Simple • Java Is Object-Oriented • Java Is Distributed • Java Is Interpreted • Java Is Robust • Java Is Secure • Java Is Architecture-Neutral • Java Is Portable • Java's Performance • Java Is Multithreaded • Java Is Dynamic Write once, run anywhere With a Java Virtual Machine (JVM), you can write one program that will run on any platform.

12. Characteristics of Java • Java Is Simple • Java Is Object-Oriented • Java Is Distributed • Java Is Interpreted • Java Is Robust • Java Is Secure • Java Is Architecture-Neutral • Java Is Portable • Java's Performance • Java Is Multithreaded • Java Is Dynamic Because Java is architecture neutral, Java programs are portable. They can be run on any platform without being recompiled.

13. Characteristics of Java • Java Is Simple • Java Is Object-Oriented • Java Is Distributed • Java Is Interpreted • Java Is Robust • Java Is Secure • Java Is Architecture-Neutral • Java Is Portable • Java's Performance • Java Is Multithreaded • Java Is Dynamic

14. Characteristics of Java • Java Is Simple • Java Is Object-Oriented • Java Is Distributed • Java Is Interpreted • Java Is Robust • Java Is Secure • Java Is Architecture-Neutral • Java Is Portable • Java's Performance • Java Is Multithreaded • Java Is Dynamic Multithread programming is smoothly integrated in Java, whereas in other languages you have to call procedures specific to the operating system to enable multithreading.

15. Characteristics of Java • Java Is Simple • Java Is Object-Oriented • Java Is Distributed • Java Is Interpreted • Java Is Robust • Java Is Secure • Java Is Architecture-Neutral • Java Is Portable • Java's Performance • Java Is Multithreaded • Java Is Dynamic Java was designed to adapt to an evolving environment. New code can be loaded on the fly without recompilation. There is no need for developers to create, and for users to install, major new software versions. New features can be incorporated transparently as needed.

16. JDK Versions • JDK 1.02 (1995) • JDK 1.1 (1996) • JDK 1.2 (1998) • JDK 1.3 (2000) • JDK 1.4 (2002) • JDK 1.5 (2004) a. k. a. JDK 5 or Java SE 5 • JDK 1.6(2006) a. k. a. JDK 6 or Java SE 6

17. JDK Editions • Java Standard Edition (J2SE) • J2SE can be used to develop client-side standalone applications or applets. • Java Enterprise Edition (J2EE) • J2EE can be used to develop server-side applications such as Java servlets and Java ServerPages. • Java Micro Edition (J2ME). • J2ME can be used to develop applications for mobile devices such as cell phones. This course uses J2SE to introduce Java programming.

18. Java IDE Tools • Borland JBuilder • NetBeans Open Source by Sun • Sun ONE Studio by Sun MicroSystems • Eclipse Open Source by IBM (preferred in this course)

19. Introductionto Classes and objects • Agenda • What is an object oriented view of programming? • What is a class? • How to define a class? • Creating and using an object

20. What is an object oriented view of programming Suppose I want to invite my friends Tom, Liz and Rita to meet me for coffee at Tim Horton’s in the Devonshire Mall at 8PM today. Approach 1: Give a complete and very detailed set of instructions on how to go from the University to Tim Horton’s. In this approach, every one exactly follows my instructions.

21. What is an object oriented view of programming Approach 2: Simply tell my friends “ Pl meet me for coffee at 8 this evening at Tim Horton’s in the Devonshire Mall” Here each person follows his/her own way of interpreting my message and reacting to it. I don’t know and I don’t care the specific mechanism used by each individual in response to my message.

22. A model for this approach • Community of interacting agents called objects • Each object provides services • All action is initiated by a message to an object

23. Object oriented view • Importance of information hiding • Service oriented view of the world

24. Notion of classes and objects • Every time I use the cookie cutter, I get a cookie ready for baking. • Each cookie looks exactly like the others • View my cookie cutter as a template My Cookie cutter

25. Class - a template for similar objects • Class definition • What are the properties of the class? • What are the capabilities of the class? • Worker class • How to characterise an object? • name, age, place_working • What can an object do? • change the place of work • describe the object as a string

26. Creating an object • First step is to define the class if needed • Use the class as a template to create objects • All objects of the same class has the same set of properties and capabilities

27. Class Hierarchies and inheritance Notion of superclass and subclasses

28. Defining a class public class worker { String Name; // Example of a variable int age; String placeWorking; public void ChangeJob(String NewPlace) // Method {placeWorking = NewPlace; } // Other methods as needed public worker(String WorkerName) // Constructor {Name = WorkerName; } }

29. How to use the services of a class • A service => a method • An object of the class must exist for nonstatic methods worker w; w = new worker( “Jim”);//use of constructor • Use service => invoke right method w. ChangeJob(“Ford, Windsor”);

30. Thinking About Objects • Objects • Reusable software components that model real-world items • Look all around you • People, animals, plants, cars, etc. • Attributes • Size, shape, color, weight, etc. • Behaviors • Babies cry, crawl, sleep, etc.

31. Java Class Libraries • Classes • Include methods that perform tasks • Return information after task completion • Include variables defining properties of class • Used to build Java programs • Java contains class libraries • Known as Java APIs (Application Programming Interfaces) • http://java.sun.com/j2se/1.5.0/docs/api/

32. Basics of a Typical Java Environment • Java programs normally undergo five phases • Edit • Programmer writes program (and stores program on disk) • Compile • Compiler creates bytecodes from program • Load • Class loader stores bytecodes in memory • Verify • Verifier ensures bytecodes do not violate security requirements • Execute • Interpreter translates bytecodes into machine language

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

34. Compiling Java Source Code You can port a source program to any machine with appropriate compilers. The source program must be recompiled, however, because the object program can only run on a specific machine. Nowadays computers are networked to work together. Java was designed to run object programs on any platform. With Java, you write the program once, and compile the source program into a special type of object code, known as bytecode. The bytecode can then run on any computer with a Java Virtual Machine, as shown below. Java Virtual Machine is a software that interprets Java bytecode.

35. Thinking About Objects (60-322) • Object-oriented design (OOD) • Models real-world objects • Models communication among objects • Encapsulates attributes and operations (behaviors) • Information hiding • Communication through well-defined interfaces • Object-oriented language • Programming in object oriented languages is called object-oriented programming (OOP) • Java

36. Thinking About Objects • Object-Oriented Analysis and Design (OOA/D) • Essential for large programs • Analyze program requirements, then develop solution • UML • Unified Modeling Language

37. A First Program in Java: Printing a Line of Text • Modifying Our First Java Program • Displaying Text in a Dialog Box • Another Java Application: Adding Integers • Memory Concepts • Arithmetic • Decision Making: Equality and Relational Operators

38. A Simple Java Program Listing 1.1 //This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); } }

39. Creating and Editing Using NotePad To use NotePad, type notepad Welcome.java from the DOS prompt.

40. Creating and Editing Using WordPad To use WordPad, type write Welcome.java from the DOS prompt.

41. Creating, Compiling, and Running Programs

42. Comments In Java, comments are preceded by two slashes (//) in a line, or enclosed between /* and */ in one or multiple lines. When the compiler sees //, it ignores all text after // in the same line. When it sees /*, it scans for the next */ and ignores any text between /* and */.

43. Discuss four small Java programs Welcome1.java Welcome2.java Welcome3.java Welcome4.java

44. Displaying Text in a Message Dialog Box you can use the showMessageDialog method in the JOptionPane class. JOptionPane is one of the many predefined classes in the Java system, which can be reused rather than “reinventing the wheel.”

45. The showMessageDialog Method JOptionPane.showMessageDialog(null, "Welcome to Java!", “Display Message", JOptionPane.INFORMATION_MESSAGE));

46. Two Ways to Invoke the Method There are several ways to use the showMessageDialog method. For the time being, all you need to know are two ways to invoke it. One is to use a statement as shown in the example: JOptionPane.showMessageDialog(null, x, y, JOptionPane.INFORMATION_MESSAGE)); where x is a string for the text to be displayed, and y is a string for the title of the message dialog box. The other is to use a statement like this: JOptionPane.showMessageDialog(null, x); where x is a string for the text to be displayed.

47. The exit Method Prior to JDK 1.5, you have to invoke System.exit() to terminate the program if the program uses JOptionPane dialog boxes. Since JDK 1.5, it is not necessary.

48. Escape characters • Backslash ( \ ) • Indicates special characters be output

49. Another Java Application: Adding Integers Addition.java

50. sum 0 sum 3 Memory Concepts • Visual Representation • Sum = 0; number1 = 1; number2 = 2; • Sum = number1 + number2; after execution of statement