Introduction to Java 2 Programming

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

2. Overview • Reviewing the Java API • Some packages we’ve 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 we’ve 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. Don’t rewrite original class • But don’t overuse it, aggregation is often better • Never break encapsulation • Practice “defensive programming” • Don’t return objects you don’t 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 don’t worry about getting it right first time • Learn from others • Read other peoples code, see how they’ve 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 aren’t 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