java - check empty edit text in an alert dialog android -

i have following code checking empty edit text in alert dialog, not working

    if (mphonenumber == null) {         mphonenumber = getnumber();         if (mphonenumber == "error") {              final alertdialog.builder alert = new alertdialog.builder(this);             alert.settitle("warrning");             alert.setmessage("please set phone number");             final edittext input = new edittext(this);             input.setinputtype(inputtype.type_class_phone);             alert.setview(input);             alert.setpositivebutton("ok",new dialoginterface.onclicklistener() {                         public void onclick(dialoginterface dialog,int whichbutton) {                             string value = input.gettext().tostring();                             while (value.isempty())                             {                                 alert.settitle("warrning");                                 alert.setmessage("please set phone number");                                 alert.setview(input);                                 alert.setpositivebutton("ok",new dialoginterface.onclicklistener() {                                             public void onclick(dialoginterface dialog,int whichbutton) {                                                 string value = input.gettext().tostring();}});                             }                             string result = setnumber(value);                             mphonenumber = value;                             int userserviceid = calllogin(mphonenumber);                             if (userserviceid > 0) {                                 intent service = new intent(mainscreeen.this,                                         recipeservice.class);                                 service.putextra("userid", userserviceid);                                 startservice(service);                             } else {                                 intent reg = new intent(mainscreeen.this,regsteration.class);                                 reg.putextra("phonenumber", mphonenumber);                                 startactivity(reg);                             }                         }                     });             alert.show(); 

i need enforce user inter his/her phone number , not leaving edit text being empty, used while loop not working

it looks trying compare string values. can't this

if (mphonenumber == "error") 

change to

if("error".equals(mphonenumber)) 

== compares if same object strings not if have same value. doing way shouldn't need null check because "error" won't equal mphonenumber if mphonenumber null