Is there an equivalent to memcpy() in Java?

Question

I have a byte[] and would like to copy it into another byte[]. Maybe I am showing my simple \'C\' background here, but is there an equivalent to memcpy() on byte arrays in

Answer 1

Use byteBufferViewVarHandle or byteArrayViewVarHandle.

This will let you copy an array of "longs" directly to an array of "doubles" and similar with something like:

public long[] toLongs(byte[] buf) {
    int end = buf.length >> 3;
    long[] newArray = new long[end];
    for (int ii = 0; ii < end; ++ii) {
        newArray[ii] = (long)AS_LONGS_VH.get(buf, ALIGN_OFFSET + ii << 3);
    }
}

private static final ALIGN_OFFSET = ByteBuffer.wrap(new byte[0]).alignmentOffset(8); 
private static final VarHandle AS_LONGS_VH = MethodHandles.byteArrayViewVarHandle(long[].class, ByteOrder.nativeOrder());

This will let you do the bit hacking like:

float thefloat = 0.4;
int floatBits;
_Static_assert(sizeof theFloat == sizeof floatBits, "this bit twiddling hack requires floats to be equal in size to ints");
memcpy(&floatBits, &thefloat, sizeof floatBits);