title: Am I right about the major differences between activity, service and broadcast in Android
body: <p>I found Android's key components a little bit confusing, thus I have made a chart for me to remember. But I am not sure whether I am right or not. (It will be disastrous if I remember wrong things correct.) Thus I have decided to post a question on Stack Overflow to check.</p>
  
  <pre>
  item       | ____ground | runtime reg? | 1 to ?
  -----------------------------------------------------------------------------------
  activity   | foreground | no           | 1 (multiple candidates for implicit, finally still 1)
  -----------------------------------------------------------------------------------
  service    | background | no           | 1 (multiple candidates for implicit, finally still 1)
  -----------------------------------------------------------------------------------
  broadcast  | background | yes          | all (may not reach all if aborted for ordered)
  </pre>