Java Packages and Libraries

1. Java Packages and Libraries M Taimoor Khan taimoorkhan@ciit-attock.edu.pk

2. Content • What is a class library? • What is a package? • Java class libraries, what do they provide? • The root class : java.lang.object

3. The Java class library • Thousands of classes • Tens of thousands of methods • Many useful classes that make life much easier • A Java programmer must be able to work with the libraries • http://java.sun.com/javase/reference/api.jsp

4. Working with the library You should: • know some important classes by name • know how to find out about other classes • http://java.sun.com/javase/6/docs/api/ Remember: • We only need to know the interface, not the implementation The public face of the class

5. The exit condition String input = reader.getInput(); if(input.startsWith("bye")) { finished = true; } • Where does ‘startsWith’ come from? • What is it? What does it do? • How can we find out?

6. Reading class documentation • Documentation of the Java libraries in HTML format; • Readable in a web browser • Class API: Application Programmers’ Interface • Interface description for all library classes

7. Interface vs implementation The documentation includes • the name of the class;

8. Interface vs implementation The documentation includes • a general description of the class;

9. Interface vs implementation The documentation includes • a list of constructors

10. Interface vs implementation The documentation includes • a list of methods

11. Interface vs implementation The documentation includes • return values and parameters for constructors and methods

12. Interface vs implementation The documentation does not include • private fields (most fields are private) • private methods • the implementation (source code) for each method

13. Using library classes • Classes from the library must be imported using an import statement (except classes from java.lang). • They can then be used like classes from the current project. • http://java.sun.com/docs/books/tutorial/java/package/usepkgs.html • “The Java compiler automatically imports” • java.lang package • the package of the current file source code

14. Packages and import • Classes are organised in packages. • Single classes may be imported:import java.util.ArrayList; • Whole packages can be imported:import java.util.*; Some of the Packages listed in the API Packages are NOT hierarchical Using “import java.awt.*;” does not import java.awt.color.*;

15. Using Random • The library class Random can be used to generate random numbers import java.util.Random; ... Random randomGenerator = new Random(); ... int index1 = randomGenerator.nextInt(); int index2 = randomGenerator.nextInt(100);

16. Generating random responses public Responder() { randomGenerator = new Random(); responses = new ArrayList<String>(); fillResponses(); } public String generateResponse() { int index = randomGenerator.nextInt(responses.size()); return responses.get(index); } public void fillResponses() { ... }

17. Java Packages • An overview can be found at this link • http://java.sun.com/javase/6/docs/api/overview-summary.html

18. Java Packages • Inside each package you will find • Interfaces • Classes • Enumerations • Exceptions

19. java.lang • “Provides classes that are fundamental to the design of the Java programming language.” • Boolean, Byte, Double, Integer, Long, String • Math • System • Object

20. java.util • “Contains the collections framework…date and time facilities,… string tokenizer.. random-number generator..” • ArrayList<E>, LinkedList<E>, Stack<E> • Calendar, Date • Formatter • Scanner • StringTokenizer • Random • Iterator<E>

21. java.io • “Provides for system input and output through data streams, serialization and the file system.” • Console • File • FileReader • BufferedInputStream • StreamTokenizer

22. GUI libraries • java.awt • java.awt.Event • javax.imageio • javax.swing • http://java.sun.com/docs/books/tutorial/uiswing/

23. All classes are Objects

24. Packages

26. Reading & Exercises • P136 – p147 • Collections • http://java.sun.com/docs/books/tutorial/collections/index.html • Swing • http://java.sun.com/docs/books/tutorial/ui/index.html • Classes and Objects • http://java.sun.com/docs/books/tutorial/java/javaOO/index.html • Generics • http://java.sun.com/docs/books/tutorial/java/generics/index.htm

27. References • http://java.sun.com/javase/reference/api.jsp • http://java.sun.com/docs/books/tutorial/java/package/managingfiles.html • http://en.wikipedia.org/wiki/Classpath_(Java) • http://condor.depaul.edu/~glancast/224class/docs/lecJun16.html