title: UI can be updated although i call .observeOn(Schedulers.newThread())
body: <p>I am new to <code>RXJAVA 2</code>. </p>
  
  <p>While learning it I reliazed that even I call observeOn (also not)on different thread using  <code>.observeOn(Schedulers.newThread())</code> I can still change text of textview.</p>
  
  <p>I am really confused how it can happen even though I dont call  <code>.observeOn(AndroidSchedulers.mainThread())</code></p>
  
  <p>Do you not think I should get an exception saying I can not update <code>UI</code> without calling main thread?   </p>
  
  <p>My Code :  </p>
  
  <pre><code>public class TestData {
  
      public static void getData(TextView txt){
          List&lt;UserInfo&gt; mUSerInfoList=new ArrayList&lt;&gt;();
  
          UserInfo userInfo1=new UserInfo();
          userInfo1.setName("X");
  
          UserInfo userInfo2=new UserInfo();
          userInfo2.setName("Y");
  
          UserInfo userInfo3=new UserInfo();
          userInfo3.setName("Z");
  
          UserInfo userInfo4=new UserInfo();
          userInfo4.setName("A");
  
          UserInfo userInfo5=new UserInfo();
          userInfo5.setName("B");
  
          mUSerInfoList.add(userInfo1);
          mUSerInfoList.add(userInfo2);
          mUSerInfoList.add(userInfo3);
          mUSerInfoList.add(userInfo4);
          mUSerInfoList.add(userInfo5);
  
          Observer&lt;UserInfo&gt; observer=new Observer&lt;UserInfo&gt;() {
              @Override
              public void onSubscribe(Disposable d) {
  
              }
  
              @Override
              public void onNext(UserInfo userInfo) {
  
                txt.setText(Thread.currentThread().getName());
  
              }
  
              @Override
              public void onError(Throwable e) {
  
              }
  
              @Override
              public void onComplete() {
  
              }
          };
  
          Observable.fromIterable(mUSerInfoList)
              .subscribeOn(Schedulers.newThread())
              .observeOn(Schedulers.newThread())
              .subscribe(observer);
      }
  }
  </code></pre>
  
  <p>and I call those on MainActivity</p>
  
  <pre><code>TextView txt=findViewById(R.id.txtView);
  TestData.getData(txt);
  </code></pre>