Introduction to Java

1. Introduction toJava

2. Java Characteristics • Simple (relatively) • Object-Oriented • Distributed • Interpreted • Robust and Reliable • Secure and safe (relatively) • Platform-Independent (Architecture-Neutral) • Distributed and Portable • Fast (but not the fastest) • Multithreaded

3. Object Oriented Programming • Encapsulation: keeping data and its related functionality together (non-OOP left them independent) • Data hiding: providing an interface to the user, and hiding the implementational details of this interface. This leads to simpler programming tasks. • Inheritance: ability for one class to inherit properties (data and functionality) from other classes. This leads to reusable code. (Classes are arranged in a hierarchy of classes (categories) and subclasses (sbucategories) • Polymorphism: ability for the same message to be interpreted by objects of different types in different ways. Instances Classes

4. No Source Code file (*.java) Compile (using javac.exe) Syntax OK? No Yes Logic OK? Execute the bytecode (using java.exe) Bytecode Class files (*.class) Yes Turn it in to Mitri!! The Java Programming Process Write Source Code in Java java.exe is the VIRTUAL MACHINE

5. Anatomy of a Java Program • Comments – documentation. Compiler ignored these. • Reserved Words – keywords of the language. • Modifiers – keywords that describe properties of methods, classes, or variables. • Statements – action instructions telling the CPU what to do. • Blocks – groups of statements enclosed in { and } • Classes – object-oriented constructs involving methods and variables; arranged in inheritance hierarchies. • Methods – functions, members of classes. • The main method – the starting point of a Java application. • Package – group of related classes.

6. A Simple Application Example 1.1 //Welcome.java: This application program prints // Welcome to Java! package chapter1; public class Welcome { public static void main (String[] args) { System.out.println("Welcome to Java!"); } }

7. A Simple Application Example 1.1 //Welcome.java: This application program prints // Welcome to Java! package chapter1; public class Welcome { public static void main (String[] args) { System.out.println("Welcome to Java!"); } } Comments…use // for single line or /* */ for multiple lines

8. A Simple Application Example 1.1 //Welcome.java: This application program prints // Welcome to Java! package chapter1; public class Welcome { public static void main (String[] args) { System.out.println("Welcome to Java!"); } } Package – indicates a grouping of classes.

9. A Simple Application Example 1.1 //Welcome.java: This application program prints // Welcome to Java! package chapter1; public class Welcome { public static void main (String[] args) { System.out.println("Welcome to Java!"); } } Reserved words – keywords of the language with specific meaning to the compiler.

10. A Simple Application Example 1.1 //Welcome.java: This application program prints // Welcome to Java! package chapter1; public class Welcome { public static void main (String[] args) { System.out.println("Welcome to Java!"); } } Modifiers – reserved words that specify characteristics or properties of data, methods, and classes.

11. A Simple Application Example 1.1 //Welcome.java: This application program prints // Welcome to Java! package chapter1; public class Welcome { public static void main (String[] args) { System.out.println("Welcome to Java!"); } } Statements – action instructions. Always end with semicolon (;)

12. A Simple Application Example 1.1 //Welcome.java: This application program prints // Welcome to Java! package chapter1; public class Welcome { public static void main (String[] args) { System.out.println("Welcome to Java!"); } } Blocks – groups of statements (sometimes called compound statements). Enclose classes, method statements, or statements inside controls structures. Can be nested.

13. A Simple Application Example 1.1 //Welcome.java: This application program prints // Welcome to Java! package chapter1; public class Welcome { public static void main (String[] args) { System.out.println("Welcome to Java!"); } } Classes – complex data structures encapsulating data and actions. Classes are composed of methods (functions) and variables (attributes)

14. A Simple Application Example 1.1 //Welcome.java: This application program prints // Welcome to Java! package chapter1; public class Welcome { public static void main (String[] args) { System.out.println("Welcome to Java!"); } } Methods – named blocks of statements that can be called, take arguments (parameters), return values. Note: all Java applications must have a main method as an entry point to the program.

15. Options for Building and Running Java Applications • Command Line (in DOS mode) • Get into command window • Call JDK programs for operations • Text-mode debugging • Using an Integrated Development Environment (e.g. NetBeans) • GUI interface • Menus/toolbars for operations • Graphical debugging We’ll discuss this later

16. Sun’s Java Development Kit (JDK) • Includes the following tools • found in bin subdirectory of the java directory: • Java Compiler (javac.exe) • Java Virtual Machine (java.exe) • Java AppletViewer (AppletViewer.exe) • Java Debugger (jdb.exe) • Where to get the JDK • from http://java.sun.com/javase/downloads/netbeans.html • also includes Netbeans IDE It’s Free and Open Source!!!

17. Using Command-Line Technique for Writing, Compiling and Running Java Applications • Use any text editor to create your .java source code file (for example, Notepad). • Copy the compile.bat and run.bat files (available for download from my web site) to the same folder as your .java source code file. • Make sure the path in the batch files are correct (see next slide). • Use the Command Prompt (DOS window) to access the folder and run the batch files.

18. File Paths • If you installed the Java SDK and NetBeans from Sun’s Java Site, the path to your file will be: • c:\Program Files\Java\jdk1.5.0_12 • If you are using java in the lab (installed on the D: drive), the path to the JDK is: • D:\Program Files\Java\jdk1.5.0_12 In both cases, the javac.exe and java.exe programs are in the bin subfolder

20. What is NetBeans? • Integrated Development Environment (IDE) • Analogous to Microsoft Visual Studio • Tools include: • Project workspace • Color-coded, smart editing • GUI building tools (e.g. form builders) • Compiler • Execution • Debugging tool

21. What is NetBeans? (continued) • Can build entire projects consisting of multiple source files and classes • Includes GUI building tools for easy placement of components (controls) • Like form builders in VB • Menu/toolbar interfaces for compile/execute/debug

22. NetBeans Interface (for edit, compile, execute, and debug) Projects window Editor window Output window Debug windows

23. Using the Examples from Liang’s Textbook • All Textbook examples are located downloadable from my web site. • Create a Liang7eSamples project using NetBeans. • In the Liang7eSamples folder, there is a src subfolder. In that subfolder, you can copy the folders I provide in my examples…each subfolder of src is a package, and contains the java programs of the chapter • NOTE: Liang has a web site with more resources: http://prenhall.com/liang.