Java 7 - What's new? Release date, code examples and performance

http://inebium.com/post/java-7-new-release-performance-code

by alrex021 • 16 years ago

67 25 16 years ago

aphyr• 16 years ago

There's a lot of good stuff here--notably the (finally) decent support for literal sets, arrays, and maps in JSON style... but most importantly, closures! I am so sick and tired of creating one-off anonymous classes just to pass a function around. Unfortunately you can only use them with final variables. Ah, well...

http://blogs.sun.com/mr/entry/closures

ericlavigne3• 16 years ago

The top priority is still to avoid confusing programmers, and closing over non-final variables can lead to some very confusing situations. For example:

List list = Lists.newArrayList(); for(Integer i = 0; i < 10; i++) { list.add(fn [x] { i + x }); }

Think you just created a list of 10 functions that each add a different number to their argument? If you closed over the i variable, that variable changed and by the end of the loop is 9. All of the functions return their argument plus 9.

In any case, I can't wait to get some form of closures in Java. Best case would be to get a job using a decent programming language, but closures and various data type literals could go a long way to dull the pain until then.

extension3• 16 years ago

This certainly does appear to be a common point of confusion for languages that have both mutable variables and closures:

http://stackoverflow.com/questions/271440/c-captured-variabl... http://stackoverflow.com/questions/233673/lexical-closures-i...

I remember bumping into the issue myself in JavaScript, but only once. After I became aware of the concept, it was never a problem again, in any language. Those one-time issues don't worry me. It's the problems that come up over and over again that are worth fixing at the language level.

A good way to explain it is to analogize captured variables to variables used in the body of a loop or conditional. Variables are only ever created when a declaration is evaluated, and a variable has exactly one value at any given time. The obvious alternative, copying the variable when it's closed over, seems more confusing to me. And the current restriction, that captured variables are final, is just going to force hackery.

Ultimately, if Java grunts want closures, they will have to understand variable capturing. It's part of the package.

Dellort• 16 years ago

Where can I go for more benchmarks?

vlisivka4• 16 years ago

If you cannot wait for Java 1.7, use usual trick with anonymous classes and static initializer block:

  Java 1.7:
  List<String> list = ["item"];

  Java 1.2:
  List<String> list = new AList<String>() {{ items=["item"]; }};

where:

  public class AList<T> implements List<T> {
    protected T[] items;
    // Implementation
 }

  Set<String> set = {"item"};
  Set<String> set = new ASet<String>() {{ items={"item"}; }};

  Map<String, Integer> map = {"key" : 1};
  Map<String, Integer> map = new AMap<String, Integer>() {{ keys=["key"]; values=[1]; }};

I can post detailed explanation and examples of this technique, which I love to use, in my blog, if somebody will be interested. (English is foreign language to me).

It is much better than to use full blown implementation and bunch of setters just to pass around one or two elements.

I often use this technique to pass optional data to/from methods or to program in declarative style in java.

ericlavigne3• 16 years ago

Or use Google Collections in Java 1.5 or higher.

http://code.google.com/p/google-collections/

List<String> list1 = Lists.newArrayList("item"); List<String> list2 = Lists.newArrayList("item1","item2");

Of course, none of these workarounds are close to what Java 7 offers. Just a few more months :-)

vlisivka4• 16 years ago

> Or use Google Collections in Java 1.5 or higher.

See Sandman reply.

Sandman2• 16 years ago

For lists, you can also do this: List<String> strings = new ArrayList<String> (Arrays.asList("one", "two", "three"));

vlisivka4• 16 years ago

Yes, you right. This is very cheap way to initialize ArrayList. I use it too.

Did you know something similar for Map's? :-)

catch404• 16 years ago

I'm guessing the same applies for C#, does anyone know if there are language supported features for lists like the new java ones for C#?

lenni• 16 years ago

I'm wondering how the implementation is chosen when you do something like

  List<String> list = ["ham","eggs"];

Is it a linked list, an array list, a vector ... ?

_delirium4• 16 years ago

The compiler chooses, probably based on the type and number of elements. In theory it should know how to do this efficiently, because this syntax returns only immutable collections, so the compiler knows up front exactly what the collection will ever contain.

This is what the proposal says about that decision:

  It is likely to be higher in space and time performance, in that the
  compiler can choose efficient implementations for small collections
  (such as empty collections and singletons).  On the other hand, it is
  less flexible, in that you cannot specify the implementation type.

From: http://mail.openjdk.java.net/pipermail/coin-dev/2009-March/0...

abalashov• 16 years ago

Why does it only return immutable collections? Because the spec says so, or because there is some principle suggesting that it should?

Personally, my first instinct was to read the syntax as a form of initialisation, not something that would bar me from adding or deleting elements after the set is instantiated.

mhansen• 16 years ago

How does this maintain the List interface, which defines methods for mutating the collection through methods such as add() and remove()?

If I get a variable of type List, I expect to be able to change the list.

vlisivka4• 16 years ago

Why you worry?

kentosi• 16 years ago

Good point. I see this as a good mechenism for allowing immutable lists (in which case it probably doesn't matter). But for mutable ones, you would probably want control over the datastructure.

The only way of allowing the programmer to do this, that I can think of for now, is by casting perhaps?

List<String> list = (LinkedList)["ham","eggs"];

Just an idea ...

noss• 16 years ago

List<String> list = new LinkedList<>(["ham","eggs"]);

Java 7 - What's new? Release date, code examples and performance

Related Stories