What's invokedynamic and how do I use it?

问题:

I keep hearing about all the new cool features that are being added to the JVM and one of those cool features is invokedynamic. I would like to know what it is and how does it make reflective programming in Java easier or better?

回答1:

It is a new JVM instruction which allows a compiler to generate code which calls methods with a looser specification than was previously possible -- if you know what "duck typing" is, invokedynamic basically allows for duck typing. There's not too much you as a Java programmer can do with it; if you're a tool creator, though, you can use it to build more flexible, more efficient JVM-based languages. Here is a really sweet blog post that gives a lot of detail.

回答2:

Some time ago, C# added a cool feature, dynamic syntax within C#

Object obj = ...; // no static type available 
dynamic duck = obj;
duck.quack(); // or any method. no compiler checking.

Think of it as syntax sugar for reflective method calls. It can have very interesting applications. see http://www.infoq.com/presentations/Statically-Dynamic-Typing-Neal-Gafter

Neal Gafter, who's responsible for C#'s dynamic type, just defected from SUN to MS. So it's not unreasonable to think that the same things had been discussed inside SUN.

I remember soon after that, some Java dude announced something similar

InvokeDynamic duck = obj;
duck.quack(); 

Unfortunately, the feature is no where to be found in Java 7. Very disappointed. For Java programmers, they have no easy way to take advantage of invokedynamic in their programs.