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19-Jul-10

Java 1.5

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Reason for changes

The new language features all have one thing in

common: they take some common idiom and provide

linguistic support for it. In otherwords, they shift the

responsibility forwriting the boilerplate code from theprogrammer to the compiler.

--Joshua Bloch, senior staffengineer, Sun Microsystems

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New features--maybe

Generics Compile-time type safety for collectionswithout casting

Enhanced for loop

Eliminates the drudgery and error-proneness of iterators

Autoboxing/unboxing Avoids manual conversion between primitive types (such as int) andwrapper types (such as Integer)

Typesafeenums Provides all thewell-known benefits of the Typesafe Enum pattern

Static import Lets you avoid qualifying static members with class names

Metadata Tools to generate boilerplate code from annotations in the source code

Leads to a "declarative" programming stylewhere the programmer says

what should be done and tools emit the code to do it

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Generics

A generic is a method that is recompiled with different types as

the need arises

The bad news:

Instead of saying: List words = new ArrayList();

You'll have to say:

List words = new ArrayList();

The good news:

Provides compile-time checking to make sureyou are using the correct

type

No casting; instead of

String title = ((String) words.get(i)).toUppercase();

you use

String title = words.get(i).toUppercase();

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Enhanced for loop

Instead ofvoid cancelAll(Collection c) {

for (Iterator i = c.iterator(); i.hasNext(); ) {TimerTask tt = (TimerTask) i.next();tt.cancel();

}}

You will be able to use:void cancelAll(Collection c) {

for (Object o : c)((TimerTask)o).cancel();

} Or:

void cancelAll(Collection c) {for (TimerTask task : c)

task.cancel();}

Not everyone likes this syntax!

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Autoboxing

Java wont let you use a primitive valuewhere an object

is required--you need a wrapper

Similarly, you cant use an object where a primitive is

required--you need to unwrap it Java 1.5 makes this automatic:

Map m =

new TreeMap();

for (String word : args) {m.put(word, m.get(word) + 1);

}

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Enumerations

An enumeration, or enum, is simply a set of constants

to represent various values

Heres the old way of doing it

public final int SPRING = 0;public final int SUMMER = 1;

public final int FALL = 2;

public final int WINTER = 3;

This is a nuisance, and is error prone as well Heres the newway of doing it:

enum Season { winter, spring, summer, fall }

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Advantages of the newenum

They provide compile-time type safety

int enums don't provide any type safety at all

They provide a proper name space for theenumerated type

With int enums you have to prefix the constants to get any semblance of a

name space.

They're robust

int enums are compiled into clients, and you have to recompile clients if

you add, remove, or reorder constants.

Printed values are informative Ifyou print an int enum you just see a number.

Because they're objects, you can put them in collections.

Because they'reessentially classes, you can add arbitrary fields

and methods

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New features ofenum

public enum Coin {

penny(1), nickel(5), dime(10), quarter(25);

Coin(int value) { this.value = value; }

private final int value;

public int value() { return value; }

}

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Static import facility

import static org.iso.Physics.*;

class Guacamole {

public static void main(String[] args) {

double molecules = AVOGADROS_NUMBER * moles;...

}

}

You no longer have to sayPhysics.AVOGADROS_NUMBER

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Metadata

Boilerplate is code that is inserted over and over again,

into many different programs

The@ symbol is used to tell the compiler to fetch the

code from somewhereelse, and insert it It is unclear to me howelse this will be used

I doubt that its just an #insert facility

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Status

Java 1.5 is due out in late 2003

At this point, it seems highly unlikely that 1.5 will be out by

theend of 2003

My description is from an ancient article--May 2003

It isnt easy to find out much more than this

Lets hope for the best!

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The End