javascript - Java how to detect variable change -

i have cordova plugin , working. however, while loop wait until hashmap has seems inefficient. there better way?

public class myapp extends cordovaplugin {   static hashmap<string,string> myprop = new hashmap<string,string>();    protected void plugininitialize() {   }    public boolean execute(string action, jsonarray args, callbackcontext callbackcontext)        throws jsonexception {     if (action.equals("init")) {       appconnectionservice.requestconfig(cordova.getactivity());        init(callbackcontext);        pluginresult.status status = pluginresult.status.no_result;       pluginresult pluginresult = new pluginresult(status);       pluginresult.setkeepcallback(true);       callbackcontext.sendpluginresult(pluginresult);            return true;           }     return false;   }    private void init(final callbackcontext callbackcontext) {     while(myprop.isempty()) {      }      pluginresult result = new pluginresult(pluginresult.status.ok, myprop.get("myid"));     result.setkeepcallback(false);     callbackcontext.sendpluginresult(result);            }    public static boolean handleconfig (bundle config) {       if (config != null) {         // add entries came in config display adapter         (string key: config.keyset()) {                       myprop.put(key, config.getstring(key));         }       } else {           log.d("myapp", "failed");       }       return false;   }   } 

so on javascript part call init(), , return "myid", way waiting result busy loop:

while(myprop.isempty()) {  } 

is there more efficient , robust way wait result?

that looks place use wait , notify.

https://docs.oracle.com/javase/tutorial/essential/concurrency/guardmeth.html

http://www.java-samples.com/showtutorial.php?tutorialid=306