JDK 一段代码的疑问

open jdk 17, ByteBuffer 的一段代码

 private ByteBuffer getArray(int index, byte[] dst, int offset, int length) { if ( ((long)length << 0) > Bits.JNI_COPY_TO_ARRAY_THRESHOLD) { long bufAddr = address + ((long)index << 0); long dstOffset = ARRAY_BASE_OFFSET + ((long)offset << 0); long len = (long)length << 0; try { SCOPED_MEMORY_ACCESS.copyMemory( scope(), null, base(), bufAddr, dst, dstOffset, len); } finally { Reference.reachabilityFence(this); } } else { int end = offset + length; for (int i = offset, j = index; i < end; i++, j++) { dst[i] = get(j); } } return this; } 

我想知道这个左移 0 位目的是什么