SIPUSH pushes a signed short onto the stack。
SIPUSH is a signed integer in the range -32768 to 32767
push two-byte signed integer
sipush takes a single parameter, <n> (a 16-bit signed integer), sign extends it to a 32-bit int, and pushes the resulting int onto the operand stack.
sipush is typically more efficient than ldc. It also occupies fewer bytes in the class file.
具体目的是干什么,不知道了。