New Features of Java 5.0

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New Features of Java 5.0
Capital District Java Developers Network 12
October, 2005 Rod Sprattling Solentas, LLC
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Note To 12 October Attendees
I did my promised homework before sending this
presentation off to Anthony. Select Notes View in
PowerPoint or OpenOffice Presentation to read the
comments and clarifications. Rod Sprattling 12
October 2005
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The Big Stuff

• Generics
• Enumerations
• New concurrency constructs
• New interfaces
• Autoboxing
• New loop for/in

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Less Big Stuff

• Static imports
• varargs
• System.lang.Formatter
• Annotations
• JVM monitoring and control

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Generics

• Java Generics were strongly driven by desire for
  less fiddly Collections programming.
• Like C templates, provide compile-time
  resolution of datatype abstractions that preserve
  type safety and eliminate need for casting.
• Can employ generics in classes, interfaces and
  methods.
• Unlike C templates, Generics are more than a
  clever macro processor Java compiler keeps track
  of generics internally, and uses same class file
  for all instances.

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Generic Collections

• Six core collections interfaces are
  synchronization wrappers
• Collection abstract generic class
• List
• Set, SortedSet
• Map, SortedMap
• Non-generic collections classes (HashMap, etc.)
  still available, of course.

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Simplify Collections Use

• Java 1.4

LinkedList list new LinkedList() list.add(new
Integer(1)) Integer num (Integer) list.get(0)

• Java 5

LinkedList list new LinkedList
() list.add(new Integer(1)) Integer num
list.get(0)
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Simplify Collections Use

• Original

HashMap celebrityCrashers new
HashMap() celebrityCrashers.put( new Date(
10/05/2005 ), new String( Lindsay
Lohan ) ) Date key new Date( "10/1/2005"
) if ( celebrityCrashers.containsKey( key ) )
System.out.println( "On " key ,
(String) celebrityCrashers.get( key )
crashed a vehicle.")

• Extra Crispy

Map celebrityCrashers new
HashMap() celebrityCrashers.put(
new Date(10/05/2005), new String(
Lindsay Lohan ) ) Date key new
Date("10/05/2005") if ( celebrityCrashers.contain
sKey( key ) ) System.out.printf( "On tc, d
crashed a vehiclen key,
celebrityCrashers.get( key ) )
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Defining Generics

• Classes

class LinkedList implements List //
implementation

• Interfaces

interface List void add(E x)
Iterator iterator()

• Methods

void printCollection(Collection c)
for(Object oc) System.out.println(o)

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Wildcards

• ? extends Type a family of Type subtypes
• ? super Type a family of Type supertypes
• ? - the set of all Types, or any

public static
void sort(List list) Object a
list.toArray() Arrays.sort(a)
ListIterator i list.listIterator()
for(int j0 j i.set((T)aj)
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Enumerations

• In Java 1.4 we use Bloch's 'type safe enum'
  design pattern

// This class implements Serializable to preserve
valid equality // tests using after
deserialization. public final class PowerState
implements java.io.Serializeable private
transient final String fName private static
int fNextOrdinal 1 private final int
fOrdinal fNextOrdinal private
PowerState(String name) this.fName name
public static final PowerState ON new
PowerState("ON") public static final
PowerState OFF new PowerState("OFF") public
String toString() return fName
private static final PowerState fValues ON,
OFF private Object readResolve () throws
java.io.ObjectStreamException return
fValuesfOrdinal
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Enumerations

• A bit more concise in Java 5

public enum PowerState ON, OFF

• Enum classes
• declare methods values(), valueOf(String)
• implement Comparable, Serializeable
• override toString(), equals(), hashCode(),
  compareTo()

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java.util.concurrent

• New package that supports concurrent programming
• Executor interface executes a Runnable
• ThreadPoolExecutor class allows creation of
  single, fixed and cached thread pools
• Executor also executes Callable objects. Unlike
  Runnable, Callable returns a result and can throw
  exceptions

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New Ability Interfaces

• Iterable advertises the class implements
  Interator with hasNext(), next() methods.
  Introduced to make for/in loop work.
• Appendable implemented by classes that can have
  a char or CharSequence appended to it (e.g.,
  StringBuffer, CharBuffer)
• Readable implemented by classes that can
  sequentially copy chracters into a buffer.

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New Ability Interfaces

• Closeable, Flushable implemented by classes
  that provide close() and flush() methods
• Formattable implemented by classes that want to
  have finer control over text formatting, using
  the java.util.Formatter class, than toString()
  can give. Formatter underlays printf() and
  format()..

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Autoboxing

• Easier conversion between primative and reference
  types

// Java 1.4 List numbers new
ArrayList() numbers.add(new Integer(-1)) int i
((Integer)numbers.get(0)).intValue() // Java
5 List numbers new ArrayList() numbers.add(-1)
// Box int to Integer int i
numbers.get(0) // Unbox Integer to int
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Static Imports

• Langauge support makes it easier to import static
  members from another class. No more BigBagOf
  Constants interfaces.

import static com.solentas.Agent.RunState.NEW imp
ort static com.solentas.Agent.RunState.READY impo
rt static com.solentas.Agent.RunState.RUNNING imp
ort static com.solentas.Agent.RunState.BLOCKED im
port static com.solentas.Agent.RunState.TERMINATED
// import static com.solentas.Agent.RunState.
//.... agent.state RUNNING
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Enhanced for Loop
Collection temperatures new
LinkedHashSet() temperatures.add(105)
temperatures.add(92) temperatures.add(7) for(In
teger aTemp temperatures)
System.out.println("This temperature is "
aTemp)

• Hides the loop counter or Iterator....
• ...but therefore can't be used when your code
  needs the counter or Iterator.

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Variable Argument List

• varargs mechanism allows variable length argument
  lists. Used in System.out.printf(), format()
  method of String and java.util.Formatter

public static int min(int first, int...
rest) int min first for(int next rest)
if (next Note the last argument is typed. // C varargs are
untyped (unsafe!) // int min(int first,
...) // Cyclone C lets you type (safer!) //
int min(int first, ...int_t args)
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java.util.Formatter Class

• Provides control of string formatting akin to C's
  printf()
• Utilizes a format string and format specifiers
• Unlike C format strings, note use of as sole
  format specifier. No backslashes, such as \n

System.out.printf(s crashed on tcn,
celebName, crashDate)
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Annotations

• Let you associate metadata with program elements
• Annotation name/value pairs accessible through
  Reflection API
• Greatest utility is to tools, such as code
  analyzers and IDEs. JDK includes apt tool that
  provides framework for annotation processing
  tools.

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Annotations

• Most useful annotation to programmer_at_Override

interface Driver //... int
getDrivingSkillsIndex() public class
Celebrity implements Driver //... /
The _at_Override annotation will let the compiler
catch the misspelled getDrivinSkillsIndex().
/ _at_Override getDrivinSkillsIndex() return 0
//...
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Annotations

• Next most useful annotations to
  programmers_at_Deprecated, _at_SuppressWarnings

_at_Deprecated public class BuggyWhip ...
//... // _at_SuppressWarnings selectively turns
off javac warnings // raised by use of the -Xlint
option _at_SuppressWarnings(fallthrough) public
void iUseSloppySwitchCoding ...
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Annotations

• You can define your own (e.g., to supplant
  javadoc tags, or annotate for code management
  practices)
• See Chapter 4 of Java In A Nutshell

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Monitoring Management

• JMX API (javax.management) provides remote
  monitoring and management of applications
• java.lang.management uses JMX to define MXBean
  interfaces for monitoring and managing a running
  JVM
• MXBean interface lets you monitor class loadings,
  compilation times, garbage collections, memory,
  runtime configuration and thread info.
• MXBean also provides for granting of JVM
  monitoring and control permission

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Monitoring Management

• java.lang.instrument defines the API to define
  agents that instrument a JVM by transforming
  class files to add profiling support, code
  coverage testing
• Instrumentation agent classes define premain()
  method, which is called during startup before
  main() for each agent class specified on the Java
  interpreter command line
• Instrumentation object can register
  ClassFileTransformer objects to rewrite class
  file byte codes as they're loaded.

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References Credits

• Sun J2SE 5 tutorial http//java.sun.com/developer/
  technicalArticles/J2SE/generics/
• Java 5 In A Nutshell (O'Reilly's Nutshell Series)
• A quick tour 'round Java 5http//www.clanproduc
  tions.com/java5.html
• Type Safe Enumerationshttp//www.javapractices.
  com/Topic1.cjpLegacy