java - Application stops after progress bar reaching 100 -

i built small progress bar. when press button, progress bar starts counting, 1 100. changed button text "running" when runs. when tried change text "again?" after reached 100 (after while loop finished), application has stopped - every time. help? thank in advance.

    package com.myfirstapplication.owner.myfirstapplication;      import android.os.handler;     import android.support.v7.app.appcompatactivity;     import android.os.bundle;     import android.view.view;     import android.widget.button;     import android.widget.progressbar;     import android.widget.textclock;     import android.widget.textview;      public class mainactivity extends appcompatactivity {     progressbar pg;     button bt;     int progressstatus = 0;     textview tv;     handler handler = new handler();      protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_main);          pg = (progressbar) findviewbyid(r.id.progressbar);         bt = (button) findviewbyid(r.id.btn);         tv = (textview) findviewbyid(r.id.textid);          bt.setonclicklistener(new view.onclicklistener() {             @override             public void onclick(view v) {                 bt.settext("running.");                 progressstatus = 0;                 new thread(new runnable() {                     @override                     public void run() {                         while (progressstatus < 100) {                             progressstatus++;                             handler.post(new runnable() {                                 @override                                 public void run() {                                     pg.setprogress(progressstatus);                                     tv.settext("progress: " + progressstatus + "/" + pg.getmax());                                 }                             });                             try {                                 thread.sleep(100);                             } catch (interruptedexception e) {                                 e.printstacktrace();                             }                         }                          bt.settext("again?");                       }                 }).start();              }         });       } } 

bt.setonclicklistener(new view.onclicklistener() {         @override         public void onclick(view v) {             bt.settext("running.");             progressstatus = 0;             new thread(new runnable() {                 @override                 public void run() {                     while (progressstatus < 100) {                         progressstatus++;                         handler.post(new runnable() {                             @override                             public void run() {                                 pg.setprogress(progressstatus);                                 tv.settext("progress: " + progressstatus + "/" + pg.getmax());                             }                         });                         try {                             thread.sleep(100);                         } catch (interruptedexception e) {                             e.printstacktrace();                         }                     }                      handler.post(new runnable() {                             @override                             public void run() {                                 bt.settext("again?");                             }                         });                   }             }).start();          }     });