headphoneState.java

Awareness.SnapshotApi.getHeadphoneState(mGoogleApiClient)
                .setResultCallback(new ResultCallback<HeadphoneStateResult>() {
                    @Override
                    public void onResult(@NonNull HeadphoneStateResult headphoneStateResult) {
                        if (headphoneStateResult.getStatus().isSuccess()) {
                            HeadphoneState headphoneState =
                                    headphoneStateResult.getHeadphoneState();
                            int state = headphoneState.getState();

                            if (state == HeadphoneState.PLUGGED_IN) {
                                // Headphones plugged in
                            } else if (state == HeadphoneState.UNPLUGGED) {
                                // Headphones unplugged
                            }
                        }
                    }
                });