最后输入的为什么是4？哪里有问题

String[] cmd = { "convert", "-scale", "98x", "-quality", "80", "C:/opt/trs/data/MD/2016/04/15/W0MD20160415zurj7EINBBE7QiRFrzjU.jpeg", "C:/opt/trs/data/MD/2016/04/15/W0MD20160415zurj7EINBBE7QiRFrzjU_98.jpeg" }; Process proc = Runtime.getRuntime().exec(cmd);// 执行命令 final ByteArrayOutputStream baos = new ByteArrayOutputStream(); final InputStream pis = proc.getInputStream(); final InputStream per = proc.getErrorStream(); try { Thread t = new Thread() { public void run() { try { int a = 0; while ((a = per.read()) != -1) { baos.write(a); } } catch (Exception e) { e.printStackTrace(); } } }; t.start(); int a = 0; while ((a = pis.read()) != -1) { baos.write(a); } t.join(); int exitCode = proc.waitFor(); String msg = new String(baos.toByteArray()); System.out.println("exitCode = "+exitCode); System.out.println("msg = "+msg); } finally { if (pis != null) { try { pis.close(); } catch (Exception ex) { } } if (per != null) { try { per.close(); } catch (Exception ex) { } } }