Howto create IntBufferd from JNI?

Performance Tuning
#1

Hi there!

I just saw that according to this document http://java.sun.com/j2se/1.4.2/docs/guide/jni/jni-14.html that its just possible to create ByteBuffers from JNI.
Is it possible to create int-Buffers too from JNI or are there some magically tricks I can see an int[] out of an bytebuffer withought copying the data arround?

Thank you in advance, lg Clemens

#2

It depends:


ByteBuffer byteBuff1 = ByteBuffer.wrap(new byte[]{1, 2, 3, 4});
ByteBuffer byteBuff2 = ByteBuffer.allocateDirect(16).order(ByteOrder.nativeOrder()).put(new byte[]{1, 2, 3, 4});
        
IntBuffer intBuff1 = ByteBuffer.wrap(byteBuff1.array()).asIntBuffer();
System.out.println(intBuff1.toString());
IntBuffer intBuff2 = ByteBuffer.wrap(byteBuff2.array()).asIntBuffer();
System.out.println(intBuff2.toString());

The stuff involving byteBuff1 works perfectly fine, but with byteBuff2 it fails with an UnsupportedOperationException becuase there is no explicit array backing the buffer.

-=EDIT=-


ByteBuffer byteBuff2 = ByteBuffer.allocate(16).order(ByteOrder.nativeOrder()).put(new byte[]{1, 2, 3, 4});

This works too, so it really just depends on how they allocate the buffer in their JNI stuff!

#3

Create ByteBuffer from JNI, then view it in native order in Java as IntBuffer in native order.

If you’d like some assembly for manipulation on the native side then

ebx = GetDirectBufferAddress(JNIEnv* env, jobject buf)
next element = ebx + 4

:slight_smile: