1. Lesson 1 1 LESSON 1 l Background information l Introduction to Java Introduction and a Taste of Java

2. Lesson 1 2 Object-Oriented Concepts l What is an Object? »A software bundle of related variable & methods. Often used to model real-world objects. l What is a Method? »A function (subroutine) associated with an object.

3. Lesson 1 3 OO Concepts continued…. l What is Modularity? »The source code for an object can be written & maintained independently of the source code for other objects. »Object can be easily passed around in the system.

4. Lesson 1 4 OO Concepts continued…. l What is Encapsulation? »Data & actions are combined into a single item (a class object) & the details of the implementation are hidden. »An object has a public interface that other objects use to communicate with it. »Information hiding, Abstract data types & Encapsulation refer to basically the same idea.

5. Lesson 1 5 OO Concepts continued…. l What is a Message? »Software objects interact & communicate with each other using messages. »Message components are: –object to which message is addressed –name of the method to perform –any parameters needed by the method

6. Lesson 1 6 OO Concepts continued…. l What is a Class? »A blueprint, or prototype, that defines the variables & the methods common to all objects of a certain kind. l What is Inheritance? »A class inherits state & behaviour from its superclass. Allows code reuse.

7. Lesson 1 7 OO Concepts continued…. l What is an Interface? »A contract in the form of a collection of method & constant declarations. »“A device or a system that unrelated entities use to interact”. »When a class implements an interface, it promises to implement all of the methods declared in that interface.

8. Lesson 1 8 OO Concepts continued…. l What is Polymorphism? »Ability of one thing to have several forms, or one form to apply to several things. »E.g. two different classes can have methods with the same name.

9. Lesson 1 9 Object-Oriented Programming l OOP l A design and programming technique l Some terminology: »object - usually a person, place or thing (a noun) »method - an action performed by an object (a verb) »type or class - a category of similar objects (such as automobiles) l Objects have both data and methods l Objects of the same class have the same data elements and methods l Objects send and receive messages to invoke actions

10. Lesson 1 10 Example of an Object Class Data Items: »manufacturer’s name »model name »year made »color »number of doors »size of engine »etc. Methods: »Define/Assign data items (specify manufacturer’s name, model, year, etc.) »Change a data item (color, engine, etc.) »Display data items »Calculate cost »etc. Class: automobile

11. Lesson 1 11 Why OOP? l Save development time (and cost) by reusing code »once an object class is created it can be used in other applications l Easier debugging »classes can be tested independently »reused objects have already been tested

12. Lesson 1 12 Java Characteristics l Platform independent »Virtual machine architecture l Object-oriented l Full GUI & multimedia support »Also platform independent l Multi-threading capabilities »Parallel programs l Applications (locally) & Applets (remotely)

13. Lesson 1 13 Compilers vs. Assemblers vs. Interpreters l Compilers and Assemblers »translation is a separate user step »translation is “off-line,” i.e. not at run time l Interpreters - another way to translate source to object code »interpretation (from source to object code) is not a separate user step »translation is “on-line,” i.e. at run time Compiler, Assembler, or Interpreter Source Code Object Code

14. Lesson 1 14 Java Program Translation l Both Compilation and Interpretation l Intermediate Code: “Byte Code” »portable low-level code »similar to assembly code, but hardware independent »invisible to Java programmer l Interpreter translates from generic byte code to hardware-specific machine code Java Program Data for Java Program Java Compiler Byte-Code Program Byte-Code Interpreter Machine-Language Instructions Computer Execution of Machine-Language Instructions Output of Java Program Java Virtual Machine

15. Java Program Data for Java Program Java Compiler Byte-Code Program Byte-Code Interpreter Machine-Language Instructions Computer Execution of Machine-Language Instructions Output of Java Program Java Virtual Machine Linker Previously Compiled Helper Programs Java Program Translation Including Linker

16. Lesson 1 16 Java Virtual Machine l The JVM executes a special machine code ("bytecode") »Java compiles to *.class files l “Imaginary” computer »Simulated – by an Interpreter l Advantage »Enables platform independence l Disadvantage »Takes longer to interpret than the “norm” (compiled)

17. Lesson 1 17 Applets vs. Java Applications l Applets »Java programs intended to be downloaded via the WWW and run immediately »“little applications” »requires a web browser l Applications »Java programs intended to be installed then run »often larger applications l Slightly different programming for each, but both are easy to do