CODEWITHSUNDEEP
javamemoryunsafe
Alex Botev
Alex Botev

Reputation: 1399

java Unsafe, how to interpret memory as an other type of object?

So I've read a few articles around but essentially since I want a fast I/O, I want to write a double array to a file. To do that I need to convert it to a byte array. Unfortunately this makes copying of data.

So I was wondering suing java Unsafe is it possible to make a byte[] variable which points to the address of the double[] array and just interpret the data as bytes rather than doubles? I did not manage to find anywhere so far such example, only again how to use copying memory in order to do this. Any advices are appreciated!

Upvotes: 2

Views: 635

Answers (1)

Peter Lawrey
Peter Lawrey

Reputation: 533492

If you start with a ByteBuffer you can hold it's reference and use them interchangably.

ByteBuffer bb = ByteBuffer.allocateDirect(8 * n_doubles);
DoubleBuffer db = bb.asDoubleBuffer();

You can not read/write to either and view it as bytes or doubles as the same memory is used.

If you want to avoid additional copies to a file, you can use a memory mapped region.

BTW: ByteBuffer uses Unsafe, but in a way which protects you.

Upvotes: 4

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