@Override public void enforce(Bus bus) {
      if (Looper.myLooper() != Looper.getMainLooper()) {
        throw new IllegalStateException("Event bus " + bus + " accessed from non-main thread " + Looper.myLooper());
      }
    }
A {@link ThreadEnforcer} that confines {@link Bus} methods to the main thread.
otto/src/main/java/com/squareup/otto/ThreadEnforcer.java