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7/30/2019 eclipseday2011-110511032907-phpapp02

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IBM 2011. Licensed under EPL v1.0

SE 7 : What's New!

Ayushman Jain

JDT/Core committerIBM


2/19


New features at a glance

Project Coin small enhancement and new languagefeatures.

Support for dynamic languages.

Unicode 6.0 new rupee symbol, brahmi script,emoticons.

New I/O and concurrent APIs.


3/19


Project coin features

Binary literals and underscores in literals.

Strings in switch.

@SafeVarargs - Varargs warnings.

Diamond - improved type inference for generic instance

creation.

Multi-catch and more precise rethrow.

try-with-resources (formerly known as AutomaticResource Management or ARM).


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Strings in switch When do you use a switch statement?

Valid case labels upto javaSE 6 can be Int constants

Enum constants String can also be constants!


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Safe Varargs

Variable arity method - public static Listjava.util.Arrays.asList(T... a)

If T is the parameter type with variable arity and is alsonon-reifiable, a new warning on declaration of variablearity methods with parameter of type T.

A new annotation @SafeVarargs to suppress thewarning at both declaration site and call site.


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Reifiable types A type whose type information is fully available at

runtime, that is, a type that does not lose informationin the course of type erasure.

Any type with type parameters is available to the JVM asthe raw type because of type erasure.

So List and List are both seen as Listby the JVM.

Hence parameterized types are non-reifiable.

On the other hand, types such as String are reifiable.


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Safe Varargs A variable arity parameter of a generic type can cause

heap pollution.

public static List java.util.Arrays.asList(T... a)

Heap pollution - A situation where a variable of a

parameterized type refers to an object that is not ofthat parameterized type.

Usually, the method body is well behaved and onlyiterates over the elements.

Hence, unchecked warning is mostly a distraction.


8/19


@SafeVarargs

Annotation legal on static or final variable arity methodsor constructors.

Not legal on

Fixed arity methods or constructors. Variable arity methods or constructors that are

neither final nor static.

Some java APIs already retrofitted with the annotation inJDK 7.


9/19


Binary Integer Literals and

Underscores in numeric literals

Binary integer literals structured just like hex intergerliterals. Differences:

Binary digits used instead of hex digits

0b now used instead of 0x In numeric literals, underscores now permitted as separators

between digits.

Applies to literals in any base: binary, octal, hexadecimal, ordecimal

Applies to both integer literals and floating point literals


10/19


Multi-catch and more precise

rethrow

Different catch blocks performing the same action on thecaught exception.

They can now be combined into one single catch block

using Disjunctive types.

Disjunctive type = ExceptionA | ExceptionB | ....

Disjunctive types implicitly final.

Also, now only the actually thrown exception is nowrethrown and not its parent type.


11/19


Try With Resources Language & Library changes to

Ease management of objects that require explicitfreeing/disposal/destruction.

Prevent resource leaks (handles, streams ...)

A la Destructors in C++ (and others) Library changes:

A new interface java.lang.AutoCloseable.

Libraries retrofitted to implement the new interface

Facilities to manage suppressed exceptions onjava.lang.Throwable


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What is a Resource Basically a final variable local to the try block.

Must be of type AutoCloseable. Must be initialized in the resource section.

Language guarantees that every successfullyinitialized non-null resource will be closed.

Will be closed regardless of normal or abrupt

completion.

In LIFC order: Last initialized first closed.


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Suppressed exceptions

Primary exception will be the exception seen by a usersupplied catch block.

Exception from close methods are added to the

suppressed list of primary exception (unless it is theprimary exception.)

An interested party can query and process suppressedexceptions. New APIs in class Throwable:

public final void addSuppressed(Throwable);

public final Throwable [] getSuppressed();


14/19


Diamond Improved type inference for generic instance

creation. Before,

List list = new ArrayList();

Now,

List list = new ArrayList();

Why not List list = new ArrayList() ?


15/19


Support for dynamic languages A growing interest in running programs written in

dynamic languages on JVM.

Particularly scripting languages-JRuby,Jpython,Groovy.

Motivation make implementation in such languages

efficient and fast. Current Problem - JVM instruction to invoke a method takes

method descriptor as the argument

Method descriptor is the method name, argumenttypes and the return type.

Solution new invokeDynamicinstruction and dynamiclinking through method handles.


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JVM bytecode instructions invokevirtual - Invokes a method on a class. This is the

typical type of method invocation.

invokeinterface - Invokes a method on an interface.

invokestatic - Invokes a static method on a class. This isthe only kind of invocation that lacks a receiverargument.

invokespecial - Invokes a method without reference tothe type of the receiver.

invokedynamic- enables an implementer of a dynamiclanguage to translate a method invocation intobytecode without having to specify a target type that

contains the method.


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Method handles Consider hypothetical dynamic language code

function max (x,y) {if x.lessThan(y) then y else x }

To compile this for JVM

MyObject function max (MyObject x,MyObject y) {

if x.lessThan(y) then y else x }

Or use reflection. With Java7, use method handles!


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Use Eclipse for java 7

No builds available as of today.

Setup Eclipse to work for java 7 as described

in http://wiki.eclipse.org/JDT_Core/Java7


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Thank You!

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