Extending ByteBuffer class

Asked 2009-03-08T22:34:51.023

Is there any way to create class that extends ByteBuffer class?

Some abstract methods from ByteBuffer are package private, and if I create package java.nio, security exception is thrown.

I would want to do that for performance reasons - getInt for example has about 10 method invocations, as well as quite a few if's. Even if all checks are left, and only method calls are inlined and big/small endian checks are removed, tests that I've created show that it can be about 4 times faster.

java nio bytebuffer

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2 Answers

You cant extend ByteBuffer and thanks God for.

You cant extend b/c there are no protected c-tors. Why thank god part? Well, having only 2 real subclasses ensures that the JVM can Heavily optimizes any code involving ByteBuffer.

Last, if you need to extend the class for real, edit the byte code, and just add protected attribute the c-tor and public attribute to DirectByteBuffer (and DirectByteBufferR). Extending the HeapBuffer serves no purposes whatsoever since you can access the underlying array anyways

use -Xbootclasspath/p and add your own classes there, extend in the package you need (outside java.nio). That's how it's done.

Another way is using sun.misc.Unsafe and do whatever you need w/ direct access to the memory after address().

I would want to do that for performance reasons - getInt for example has about 10 method invocations, as well as quite a few if's. Even if all checks are left, and only method calls are inlined and big/small endian checks are removed, tests that I've created show that it can be about 4 times faster.

Now the good part, use gdb and check the truly generated machine code, you'd be surprised how many checks would be removed.

I can't imagine why a person would want to extend the classes. They exist to allow good performance not just OO polymorph execution.

edit:

How to declare any class and bypass Java verifier

On Unsafe: Unsafe has 2 methods that bypass the verifier and if you have a class that extends ByteBuffer you can just call any of them. You need some hacked version (but that's super easy) of ByteBuffer w/ public access and protected c-tor just for the compiler. The methods are below. You can use 'em on your own risk. After you declare the class like that you can even use it w/ new keyword (provided there is a suitable c-tor)

public nativ


                        
                        
                            answered 2011-05-29T10:26:01.723


            
            
                
                    
                        
                            
                            
                        
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  +50 bounty for a way to circumvent the access restriction (tt cannot be
  done using reflection alone. Maybe
  there is a way using sun.misc.Unsafe
  etc.?)


Answer is: there is no way to circumvent all access restrictions in Java.


sun.misc.Unsafe works under the authority of security managers, so it won't help
Like Sarnum said: 



  ByteBuffer has package private
  abstract _set and _get methods, so you
  couldn't override it. And also all the
  constructors are package private, so
  you cannot call them.



Reflection allows you to bypass a lot of stuff, but only if the security manager allows it. There are many situations where you have no control on the security manager, it is imposed on you. If your code were to rely on fiddling with security managers, it would not be 'portable' or executable in all circumstances, so to speak.


The bottom line of the question is that trying to override byte buffer is not going to solve the issue.

There is no other option than implementing a class yourself, with the methods you need. Making methods final were you can will help the compiler in its effort to perform optimizations (reduce the need to generate code for runtime polymorphism & inlining).

                        
                        
                            answered 2011-05-27T20:03:26.420



        
        
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