What is java.lang.NullPointerException?

Question

Java

application stops when calling another user
in logs
java.lang.NullPointerException:
at com.procrea8.mabtribune.modules.mediachat.activity.CallActivity$4.onResponse (CallActivity.java:170)
line 170

public void onParticipantConnected(Room paramRoom, Participant paramParticipant)
            {
              CallActivity.this.callingText.setVisibility(8);
              MyLog.e("Participant added");
              if (CallActivity.this.callType.equals(Integer.valueOf(1)))
              {
                CallActivity.this.identityContainer.setVisibility(8);
                paramParticipant.getMedia().setListener(new Media.Listener()
                {

Answer 1

Set a breakpoint here: And see if either "this" or "callingText" is null