Java IO 中的“while (-1 != (len = in.read(b)))”

Question

我有这个（工作）代码：BufferedInputStream in = new BufferedInputStream(conn.getInputStream());byte[] b = new byte[1024];int len;while (-1 != (len = in.read(b))) {    fos.write(b, 0, len);}fos.flush();但是，如果我将 更改while (-1 != (len = in.read(b)))为while ((len = in.read(b)) > 0)，则流无法完成。为什么是这样？