1. Introduction to Java 2 Programming Lecture 10 API Review; Where Next

2. Overview Reviewing the Java API –Some packages weve seen –And some new ones… Coding and Design Tips –Tips for good Java programs Where Next? –Books, Websites, Tutorials

3. java.lang The real core of the Java API –Automatically imported by all Java classes System and Runtime classes –Access to the virtual machine –System properties –Standard input, output, error The Number classes –Boolean, Integer, Float, Double, Long, Short, etc –Provide OO version of primitive types –Provide conversion functions (e.g. to/from String) The Class and Object classes –Object is the root of the Java inheritance tree –Class is an OO description of a Java class

4. java.util Large collection utility classes, and several sub- packages Collection classes, very flexible data structures –Implementations of Set, List and Map interfaces –Arrays and Collections classes, for sorting and searching collections Calendar and Date classes for providing date utilities Other miscellaneous classes –Currency, StringTokenizer, etc

5. java.util java.util.logging –Provides access to a complete logging system, for recording application progress, error messages, etc –Very flexible (different log levels, different log formats, different log destinations) java.util.zip, java.util.jar –Classes for working with zip and jar files. –Built in compression libraries java.util.regex –Regular Expressions –Pattern matching system adopted from Perl –Very flexible way to process text strings (e.g. to extract substrings, find data, etc)

6. java.io The Java I/O classes InputStreams and OutputStreams –Reading and writing data Readers and Writers –Reading and writing text (according to a character set) File –OO representation of the file system (both files and directories)

7. java.net Socket –Standard Berkeley socket implementation for connecting to remote service –ServerSocket class for writing servers URL –Describes a remote website, and gives access to its data via a Stream HTTPURLConnection –Provides more detailed access to a remote website –E.g. follow redirects, write to remote website, etc –(but not as flexible as a true HTTP library)

8. java.rmi Remote Method Invocation A standard way to call methods on objects on a remote machine –No need to deal with networking! A Registry lists all the useful objects on the remote machine –Client gets reference to object from a registry, and then uses it as normal Remote objects have to implement an special interface –All methods throw RemoteException Very powerful

9. java.sql Java database access layer –Known as JDBC (Java DataBase Connectivity) Allows a Java application to –..get a Connection to a database –…create and execute Statements to query the database –…and then process the ResultSet that is returned All major database vendors have implemented a Java JDBC Driver –The core API describes the basic interfaces –The vendor implements that for their database system

10. java.awt Abstract Windowing Toolkit –The original way to build GUI applications in Java Limited capabilities –Few components –API poorly designed (particularly event handling) –Not entirely portable (not pure Java) Still used for some applications, but has been replaced…

11. javax.swing Java Foundation Classes (Swing) –Replacement for AWT (but does share some common classes) Much more flexible –100% Java (therefore truly portable) –More components, more sophisticated –Pluggable Look and Feel support –Better graphics support –Support for Drag and Drop, etc Some downsides, though –Can be slower than AWT –Memory hungry –Large and complex API (to meet all requirements)

12. Overview Reviewing the Java API –Some packages weve seen –And some new ones… Coding and Design Tips –Tips for good Java programs Where Next? –Books, Websites, Tutorials

13. Java Coding Tips Never re-invent the wheel! Never write a new class, if an existing one can be extended in some way –Either through inheritance (or wrapping) Look for third-party APIs –E.g. jakarta.apache.org Only then write something yourself

14. Java Coding Tips Make good use of polymorphism –Use base class references where possible Allows you to change the concrete implementation Make good use of inheritance –Add functionality by extending. Dont rewrite original class –But dont overuse it, aggregation is often better Never break encapsulation –Practice defensive programming –Dont return objects you dont want changed, copy them instead.

15. Java Coding Tips Use Collections and Iterators, not arrays and for loops –More functionality, easier to work with Spend time thinking about your object model –…but dont worry about getting it right first time Learn from others –Read other peoples code, see how theyve tackled similar problems

16. Java Coding Tips Best tip of all: Get to know the core Java API –Read through the Javadoc –Try building simple test classes to manipulate the objects

17. Where Next? The Java Tutorial –Covers all the core functionality very thoroughly –Divided into trails so easy to dip into to learn about specific functionality –(Some bits arent as up to date as they might be, however) Thinking in Java (Bruce Eckel) –Excellent OO introduction to Java programming Design Patterns (Gang of Four) –Recipes for designing OO applications Refactoring (Martin Fowler) –Improving the design of existing OO code