android - Speeding up Ip Scanner with ExecutorService reporting wrong ips -

i'm working on ip scanner scan local net live hosts. implementation uses asynctask run in background , excutorservice create pool thread faster results; however, i'm getting wrong ips. eg ips not exist on network. implementing right? how spawn multiple runnable threads , @ same time update right output. thanks

 /*        * ascyntask scan network        * should try different timeout network/devices        * try detect localhost ip addres , subnet.        * use subnet scan network        */     private class taskscannetwork extends asynctask<void, node, void> {          string subnet;         static final int lower = 1;         static final int upper = 254;         static final int timeout = 1000;            private executorservice ipscanpool;          @override         protected void onpreexecute() {             log.v("ip address: ", ip);             subnet = ip.substring(0, ip.lastindexof("."));             hostlist.clear();             scanprogress.setmax(upper);             ipscanpool = executors.newfixedthreadpool(upper);             statusmsg.settext("scanning " + subnet + ".0/24");         }          @override         protected void doinbackground(void... params) {             (int = lower; <= upper; i++) {                 ip = subnet + "." + i;                 log.v("host: ", ip);                  final node newnode = new node();                 newnode.progressbar = i;                  ipscanpool.execute(new runnable() {                     @override                     public void run() {                         try {                             inetaddress inetaddress = inetaddress.getbyname(ip);                             if (inetaddress.isreachable(timeout)) {                                 newnode.ip = ip;                             }                          } catch (unknownhostexception e) {                             e.printstacktrace();                         } catch (ioexception e) {                             e.printstacktrace();                         }                         publishprogress(newnode);                     }                 });              }              return null;         }          @override         protected void onprogressupdate(node... values) {             //only add arraylist<node> if host alive on network             if(values[0].ip != null) {                 hostlist.add(values[0]);                 networkadapter.notifydatasetinvalidated();                 toast.maketext(getapplicationcontext(), values[0].getip(), toast.length_short).show();             }             //update progress bar             scanprogress.setprogress(values[0].progressbar);         }          @override         protected void onpostexecute(void avoid) {             statusmsg.settext(subnet + ".0/24 " + " hosts");         }     }