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 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