Tiger: Java 5 Evolutions

Tiger: Java 5 Evolutions

Dott. Ing. Marco Bresciani

Tiger: Java 5 Evolutions / 2006-10-25

All rights reserved © 2005, Alcatel

Introduction
Page 2

Need improvements from previous Java versions? See this
document:
http://java.sun.com/j2se/JM_White_Paper_R6A.pdf.
All information are taken from
http://java.sun.com/developer/technicalArticles/releases/j2s
e15langfeat/index.html and
http://java.sun.com/developer/technicalArticles/releases/j2s
e50/MigrateToTiger.html and other related pages.



Agenda
Page 3

http://java.sun.com/reference/tigeradoption/;
Main New Features for the language:
 Generics;
 Enhanced for loop;
 Auto-boxing/un-boxing;
 Type-safe enumerations;
 static imports;

Other features: metadata, variable arguments, formatted
output, synchronization, …
(http://java.sun.com/j2se/1.5.0/docs/relnotes/features.html)



Overview
Page 4

Tiger, Tiger burning bright
Like a geek who works all night
What new-fangled bit or byte
Could ease the hacker's weary plight?

Boxi
ng
stati
c
XM
L

…

for

Gen enu
erics m
Meta
data
…

Misconceptions About Tiger
Page 5

Are there any misconceptions about Tiger that you care to
address?
(http://java.sun.com/developer/technicalArticles/Interviews/h
amilton_qa2.html).
One possible misconception is the idea that because this is
such a big release people should delay moving to it. This is
false. Even though this is a big release, we have been careful
to make sure it's very thoroughly tested. Our internal quality
metrics are telling us that Tiger is at a very high quality level.
I'd urge developers to plan for a fast migration to Tiger.
Graham Hamilton, Sun Fellow in the Java Platform Team, Sun
Microsystems.



Generics (Part One)
Page 6

For further help see
http://java.sun.com/j2se/1.5/pdf/generics-tutorial.pdf;
This long-awaited enhancement to the type system allows a
type or method to operate on objects of various types while
providing compile-time type safety. It adds compile-time type
safety to the Collections Framework and eliminates the
drudgery of casting.
When you take an element out of a Collection, you must
cast it to the type of element that is stored in the collection.
Besides being inconvenient, this is unsafe. The compiler does
not check that your cast is the same as the collection's type,
so the cast can fail at run time.



Generics (Part Two)
Page 7

Before the generics:

With generics:

/**
* Removes 4-letter words from c.
* Elements must be strings
*/
static void expurgate(Collection c) {
for (Iterator i = c.iterator();
i.hasNext(); ) {
if (((String) i.next()).
length() == 4) {
i.remove();
}
}
}

/**
* Removes the 4-letter words from
* c
*/
static void expurgate(
Collection<String> c) {
for (Iterator<String> I
= c.iterator();
i.hasNext(); ) {
if (i.next().length() == 4) {
i.remove();
}
}
}



Generics (Part Three)
Page 8

Runtime Exception!
import java.util.*;
public class Ex1 {
private void testCollection() {
List list = new ArrayList();
list.add(new String("Hello world!"));
list.add(new String("Good bye!"));
list.add(new Integer(95));
printCollection(list);
}
private void printCollection(
Collection c) {
Iterator i = c.iterator();
while(i.hasNext()) {
String item = (String) i.next();
System.out.println("Item: “
+ item);
}
}
public static void main(String argv[]) {
Ex1 e = new Ex1();
e.testCollection();
}
}


Compile error only!
import java.util.*;
public class Ex2 {
private void testCollection() {
List<String> list =
new ArrayList<String>();
list.add(new String("Hello world!"));
list.add(new String("Good bye!"));
list.add(new Integer(95));
printCollection(list);
}
private void printCollection(
Collection c) {
Iterator<String> i = c.iterator();
while(i.hasNext()) {
String item = i.next();
System.out.println("Item: “
+ item);
}
}
public static void main(String argv[]) {
Ex2 e = new Ex2();
e.testCollection();
}
}


Enhanced for Loop (Part 1)
Page 9

The current for statement is quite powerful and can be used
to iterate over arrays or collections.
However, it is not optimized for collection iteration, simply
because the Iterator serves no other purpose than getting
elements out of the collection.
The new enhanced for construct lets you iterate over
collections and arrays without using Iterators or index
variables.



Page 10

This:
void cancelAll(Collection<TimerTask> c) {
for (Iterator<TimerTask> i = c.iterator();
i.hasNext(); )
i.next().cancel();
}

Will become this:
void cancelAll(Collection<TimerTask> c) {
for (TimerTask t : c)
t.cancel();
}



Page 11

And this one:
public int sumArray(int
array[]) {
int sum = 0;
for(int i = 0; i <
array.length; i++) {
this.sum +=
array[i];
}
return sum;
}


Will also simplify like this:
public int sumArray(int
array[]) {
int sum = 0;
for(int i : array) {
sum += i;
}
return sum;
}


Auto-boxing & Un-boxing (Part 1)
Page 12

As any Java programmer knows, you can’t put an int (or other primitive
value) into a collection. Collections can only hold object references, so
you have to box primitive values into the appropriate wrapper class
(which is Integer in the case of int). When you take the object out of
the collection, you get the Integer that you put in; if you need an int,
you must un-box the Integer using the intValue method. All of this
boxing and un-boxing is a pain, and clutters up your code. The autoboxing and un-boxing feature automates the process, eliminating the
pain and the clutter.
Write this: Integer phoneNumber = (int)
Double.parseDouble(phoneNumberText.getText());
Instead of this: Integer phonenumber = new Integer(new
Double(Double.parseDouble(phoneNumberText.getText()))
.intValue());



Auto-boxing & Un-boxing (Part 2)
Page 13

Consider an int being stored and then retrieved from an ArrayList:
list.add(0, new Integer(59));
int n = ((Integer) (list.get(0))).intValue();
The new auto-boxing/un-boxing feature eliminates this manual
conversion. The above segment of code can be written as:
list.add(0, 59);
int n = list.get(0);
However, note that the wrapper class, Integer for example, must be
used as a generic type:
List<Integer> list = new ArrayList<Integer>();



Type-safe enum (Part 1)
Page 14

In prior releases, an enumerated type was the int Enum pattern:
public
public
public
public

static
static
static
static

final
final
final
final

int
int
int
int

SEASON_WINTER
SEASON_SPRING
SEASON_SUMMER
SEASON_FALL =

= 0;
= 1;
= 2;
3;

This pattern has many problems, such as:
 Not type-safe - Since they are just int you can pass in any other int
values.
 No namespace - You must prefix constants with a string to avoid collisions
with other int enum types.
 Brittleness – They are compile-time constants: if a new constant is added
between two existing ones or the order is changed, clients must be recompiled.
If they are not, they will still run, but their behaviour will be undefined.
 Printed values are uninformative - Because they are just ints, if you
print one out all you get is a number, which tells you nothing about what it
represents, or even what type it is.


Page 15

In 5.0, the Java programming language gets linguistic support for
enumerated types. In their simplest form, these enums look just like their
C, C++, and C# counterparts:
enum Season { WINTER, SPRING, SUMMER, FALL }
But appearances can be deceiving. Java programming language enums
are far more powerful than their counterparts in other languages, which
are little more than glorified integers. The new enum declaration defines
a full-fledged class (dubbed an enum type). In addition to solving all the
problems mentioned above, it allows you to add arbitrary methods and
fields to an enum type, to implement arbitrary interfaces, and more.
Enum types provide high-quality implementations of all the Object
methods. They are Comparable and Serializable, and the serial
form is designed to withstand arbitrary changes in the enum type.



Page 16

Note that each enum type has a static values method that returns an array
containing all of the values of the enum type in the order they are declared. This
method is commonly used in combination with the for-each loop to iterate over
the values of an enumerated type. Suppose you want to add data and behaviour
to an enum: the idea of adding behaviour to enum constants can be taken one
step further. You can give each enum constant a different behaviour for some
method.
 One way to do this by switching on the enumeration constant. This works fine, but it will
not compile without the throw statement, which is not terribly pretty. Worse, you must
remember to add a new case to the switch statement each time you add a new constant.
There is another way give each enum constant a different behaviour for some method
that avoids these problems. You can declare the method abstract in the enum type
and override it with a concrete method in each constant. Such methods are known as
constant-specific methods.

So when should you use enums? Any time you need a fixed set of constants. That
includes natural enumerated types as well as other sets where you know all
possible values at compile time, such as choices on a menu, rounding modes,
command line flags, and the like. It is not necessary that the set of constants in
an enum type stay fixed for all time. The feature was specifically designed to
allow for binary compatible evolution of enum types.


Static Imports
Page 17

To access static members, it is necessary to qualify references
with the class they came from:
double r = Math.cos(Math.PI * theta);

The static import allows unqualified access without inheriting
from the type containing the static members. Instead, the
program imports the members, either individually or “en
masse”:
import static java.lang.Math.PI;
import static java.lang.Math.*;

Once the static members have been imported, they may be
used without qualification:
double r = cos(PI * theta);



More Features & Enhancements (1)
Page 18

Concurrency:
Scanner:
The new concurrent package in J2SE The Scanner class uses the regex
5.0 is dedicated to creating and
package to parse text input and to
managing concurrent threads. This
package provides utilities that will save
convert that input into primitive
you time and trouble creating concurrent types.
applications.
Scanner scan = new Scanner(System.in);
The Concurrency Utilities packages
System.out.print("What is your name? ");
provide a powerful, extensible
String name = scan.next();
framework of high-performance
System.out.print("How old are you? ");
threading utilities such as thread pools
int age = scan.nextInt();
and blocking queues. This package
String msgPattern = "Hi {0}. You are {1}
frees the programmer from the need to years old.";
craft these utilities by hand, in much the String msg =
MessageFormat.format(msgPattern,
same manner the Collections
name, age);
Framework did for data structures.
 Additionally, these packages provide
low-level primitives for advanced
concurrent programming.

System.out.println(msg);


More Features & Enhancements (2)
Page 19

Varargs (Variable Arguments):
In past releases, a method that took an
arbitrary number of values required you
to create an array and put the values
into the array prior to invoking the
method. The varargs feature automates
and hides the process and it is upward
compatible with pre-existing APIs.

Metadata (Annotations):
The Java platform has always had
various ad hoc annotation mechanisms.
For example the @deprecated javadoc
tag is an ad hoc annotation indicating
that the method should no longer be
used.
As of release 5.0, the platform has a
public static String format(
general purpose annotation (also known
String pattern,
as metadata) facility that permits you to
Object... arguments);
define and use your own annotation
types. The facility consists of a syntax for
The three periods after the final
declaring annotation types, a syntax for
parameter's type indicate that the final
argument may be passed as an array or annotating declarations, APIs for
reading annotations, a class file
as a sequence of arguments. Varargs
representation for annotations, and an
can be used only in the final argument
annotation processing tool.
position.



Where to Get More Information (1)
Page 20

 Java Programming Language:
http://java.sun.com/j2se/1.5.0/docs/guide/language/;
 JDK 5.0 Documentation: http://java.sun.com/j2se/1.5.0/docs/;
 New Features and Enhancements JSE 5.0:
http://java.sun.com/j2se/1.5.0/docs/relnotes/features.html;
 The All-New Java 2 Platform, Standard Edition (J2SE) 5.0 Platform:
Programming with the New Language Features in J2SE 5:
http://java.sun.com/developer/technicalArticles/releases/j2se15langfe
at/;
 JSE 5.0 in a Nutshell:
http://java.sun.com/developer/technicalArticles/releases/j2se15/;
 What’s New in JavaDoc 5.0:
http://java.sun.com/j2se/1.5.0/docs/guide/javadoc/whatsnew1.5.0.html.



Where to Get More Information (2)
Page 21

 JSE 5.0: http://java.sun.com/j2se/1.5/index.jsp;
 J2SE 5.0 Adoption: http://java.sun.com/reference/tigeradoption/;
 JavaDoc – The Java API Documentation Generator:
http://java.sun.com/j2se/1.5.0/docs/tooldocs/windows/javadoc.html;
 How and When To Deprecate API:
http://java.sun.com/j2se/1.5.0/docs/guide/javadoc/deprecation/depr
ecation.html;
 How to Write Doc Comments for JavaDoc:
http://java.sun.com/j2se/javadoc/writingdoccomments/index.html;
 Java Language Specification:
http://java.sun.com/docs/books/jls/download/langspec-3.0.pdf;
 The Java Tutorial (ATTENTION: it’s based on Java 6!):
http://java.sun.com/docs/books/tutorial/;



Answer to Life, the Universe and
Everything
Page 22

Any Question?



www.alcatel.com


Tiger: Java 5 Evolutions

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