CODEWITHSUNDEEP
java
aaronqli
aaronqli

Reputation: 809

Java: Convert direct ByteBuffer to double[]

What is the best way to do that?

I tried the following:

ByteBuffer cacheBuffer=ByteBuffer.allocateDirect(nm(nLimit,0));  //where nm(nLimit,0) is a large number
double[] cache=cacheBuffer.asDoubleBuffer().array();

But I got this exception:

java.lang.UnsupportedOperationException
at java.nio.DoubleBuffer.array(Unknown Source)

Why?

Edit:

It looks like the javadoc "Returns the double array that backs this buffer (optional operation)." actually means array() method is simply returning the double array that is already backing this buffer. I thought it is going to convert the buffer to double[] somehow. So now it makes sense I got an exception.

Upvotes: 2

Views: 2691

Answers (3)

Drona
Drona

Reputation: 7234

array() is an optional operation of Buffers. Buffer implementations may/ may not support this operation. Invoke hasArray() to check if the operation is supported and then proceed accordingly.

Upvotes: 1

mc_fish
mc_fish

Reputation: 503

if you want a shallow copy, use clone()

Upvotes: -2

obataku
obataku

Reputation: 29636

This will only work if you expect your array to merely be a copy.

final DoubleBuffer buffer = cacheBuffer.asDoubleBuffer();
final double[] copy = new double[buffer.remaining()];
buffer.get(copy);

The reason your attempt fails is because array is only supported for non-direct buffers; direct buffers are not backed by an array.

Upvotes: 6

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