JAVA BASICS

1. JAVA BASICS

2. Why Java for this Project? • Its open source - FREE • Java has tools that work well with rdf and xml • Jena, Jdom, Saxon • Can be run on UNIX,Windows,LINUX,etc • GUI/Applet capabilities • Igor’s application • WE NEED TO LEARN IT ANYWAY!

3. How to run • JDK – Java Development Kit • Basic compiler, linker, and libraries • IDE – Integrated Development Environment • NetBeans – netbeans.org

4. How to run • Types of files • .java – source code • .class – executable code • .jar (java archive) - bundle of multiple files Tutorial - http://java.sun.com/docs/books/tutorial/jar/basics/index.html • Packages – groups of related classes in a directory

5. How to run • Applications • javac – java compiler • Commandline - javac classname.java • java – executes application • Commandline - java classname • Jikes – faster version of java command • http://oss.software.ibm.com • Commandline – jikes classname

6. How to run • Environment Variables • Path – searches computer for executeable • Classpath – searches computer for classes that need to be used

7. How to run • Applets – java applications that are embedded in html and run in a browser • Appletviewer – shows sample in browser • Commandline – appletviewer appletpage.html

8. How to run • Make – (if you are sick of javac and java) • Defines which components go together to make a program. • Defines how to "put the pieces together". • Keeps track of dependencies among components. • Helps avoid doing unnecessary work and forgetting to do necessary work

9. How to run • Makefile – example default: javac Animal.java note: there is a tabspace in front of javac Commandline – make - This compiles the file called Animal.java

10. How to run • Makefile – example Tiger.java: Tiger.java Animal.class javac Tiger.java Animal.class must exist for tiger.java to compile Commandline – make tiger.java

11. How to run • Makefile – example all: Tiger Animal Tiger: javac Tiger.java Animal: javac Animal.java Commandline – make all “all” triggers both Tiger and Animal to compile

12. How to run • ANT • Similar to make in that it stores in a project • Apache application • See handout

13. Java Programming • Import • “includes” a predefined java package that will be used in a program • Statements made outside of the code • Package must be contained in a directory given in the classpath • * denotes search entire directory • Example Import java.applet.Applet; Public class BinarySearch extends JApplet { …}

14. Java Programming • Important predefined java classes • Java.io.* - i/o files and streams • Java.awt.*,java.swing.* - GUI tools • Java.util.* - data structures • Java.applet.Applet – applets • Java.servlet.* - used for scripts, tomcat and other interactive servers • Java.sql.* - used for sql handling • Java.net.* - network apps

15. Java Programming • Package – used for user defined packages • Command used when wanting to include the class in a package • Used outside class declaration • Example package john.harney.example; Public class whatever {…} • Assuming the current directory is default, this statement will place the whatever.class in the default/john/harney/example directory • Commandline – javac –d . Whatever.java

16. Java Programming • General Format /*import and package statements here*/ public/private/protected class classname{ … Member variables Constructors Methods (member functions) … } • File must be saved as “classname.java” • Main (like c++) is executeable for an application (public static void main(args)) • Class must be compiled in order to be used by another class

17. Java Programming • Executable example (Welcome3.java) public class Welcome3 { // main method begins execution of Java application public static void main( String args[] ) { System.out.println( "Welcome\nto\nJava\nProgramming!" ); } // end method main } // end class Welcome3

18. Circle.java example (Java vs C++) • Class Header • Instead of: class Circle : public Point • There is: public class Circle extends Point;

19. Java Programming • Circle.java example (Java vs C++) • Member variables • Instead of: private: double radius; • There is: private double radius;

20. Java Programming • Circle.java example (Java vs C++) • Constructors • Instead of: Circle(int x,int y, double radiusValue); • There is: public circle(int x,int y, double radiusValue); Note: “public” denotes that this may be constructed outside of the class declaration

21. Java Programming • Circle.java example (Java vs C++) • Member functions (methods) • Instead of: double getRadius() { return radius; } • There is: public double getRadius() { return radius; } Note: “public” denotes that this may called outside of the class

22. Java Programming • Circle.java example //assume the compiler can find circle.class Import javax.swing.JOptionPane; //allows GUI input public class CircleImplement { // main method begins execution of Java application public static void main( String args[] ) { Circle circ = new Circle(2,2,4.0); //constructor double rad = circ.getRadius();//calls to method getRadius JOptionPane.showMessageDialog(null,rad); //prints radius } // end method main } // end class Welcome3

23. Java Programming • Other notable differences between Java and C++ • Strings are immutable • No global variables • Memory allocation is not needed (ie no pointers) • Garbage Collection • No operator overloading

24. Javadoc • Javadoc – gives info about a source file • Commandline – javadoc class.java • Gives html documentation on the variables, methods, inheritence, other comments, etc. • Format – see handout

25. JDOM • JDOM – java class that enables XML construction and parsing • Handout

26. Saxon • Saxon - http://saxon.sourceforge.net/saxon6.5.3/index.html • Supports XSLT,XPath,XQuery • Can be used with JDOM • Commandline java  classname sourcexml > destinationxml