java 6的认识

刚刚看完csdn上的文章介绍java虚拟机,觉得讲到java 6的一点新功能,我们必须知道的,要不我们就out了...

文章是一篇Danny Coward访问;英文的原连接 http://www.artima.com/lejava/articles/dynamic_languages.html

我把一些重要的地方截下来：

Java SE 6 is no longer only about the Java language: SE 6 can be used to execute dynamic scripting language code as well. According to Danny Coward, Sun's Java SE platform lead, scripting language support is merely the first step in turning the JVM into the best possible execution platform for any dynamic language. 

a new bytecode, invokedynamic, explicitly designed to support dynamic languages, about hot-swapping—the ability to change or add a method to a class at runtime—and about the goal of turning the JVM into an ideal target for dynamic language implementation.

JSR 292 is going to provide an additional bytecode that we will probably call invokedynamic. This provides an instruction to the JVM to make a method invocation, but without the types of the return value and the method parameters to be known in the bytecode.
 

大概是讲java 6的JSR 292的技术，加入了新的字节码invokedynamic，用来给其他动态语言实现，而实现了不需要知道返回类型和参数而调用方法。。。。

下面是他讲的一个例子：

Suppose what you're doing is growing a collection by a certain size, and the return type [of that method] is Collection. In JRuby, for example, that kind of method might be implemented without having a specifically typed return value. Developers may understand in their heads that what's going to be returned is a collection, but there is not a specific type of the return [value], because [Ruby] is not a statically typed language.

Creators of dynamic language engines are in the business of taking, say, Ruby code and turning that into Java bytecode. When today's JRuby engine tries to convert that method call into bytecode, it has to create a synthetic interface to represent the return type. That isn't an interface a developer creates, but is one purely created by the JRuby engine [so] that it can take that method invocation and [turn that into] the bytecode. And that was just the return type—the same holds true for method parameters and exceptions.

JSR 292 removes the need for that synthetic interface. Today, dynamic language interpreters must output the methodinvoke bytecode, even when interpreting, say, a piece of Ruby code. Tomorrow, with JSR 292, they will be using the invokedynamic version. It will streamline the engine implementations because a lot of today's engines are worrying about creating new synthetic types and doing lots of book-keeping: when a method is called in seven or eight different places, they have to re-use that synthetic type all over the place.

Interestingly, this is not a feature of the language, but a feature of the bytecode. Java developers won't ever knowingly use a feature of JSR 292—it's something that goes on under the covers. What's most fascinating about this additional bytecode is that it will be the first bytecode [in Java] that isn't used by the Java language. We're proposing to add this bytecode purely for languages like Ruby, Groovy, BeanShell, Python, and so on. We have high hopes that those languages will run more quickly on the JVM than they do today as a result.

 

好长。。。

JRuby是java 和 Ruby的联合的引擎。。。