Difference between Android Service,Thread,IntentService and AsyncTask

Service

Thread

IntentService

AsyncTask

When to use ?

Task with no UI, but shouldn't be too long. Use threads within service for long tasks.

- Long task in general.

- For tasks in parallel use Multiple threads (traditional mechanisms)

- Long task usually with no communication to main thread.
(Update)- If communication is required, can use main thread handler or broadcast intents

- When callbacks are needed (Intent triggered tasks). 

- Small task having to communicate with main thread.

- For tasks in parallel use multiple instances OR Executor 

Trigger

Call to method
onStartService()

Thread start() method

Intent

Call to method execute()

Triggered From (thread)

Any thread

Any Thread

Main Thread (Intent is received on main thread and then worker thread is spawed)

Main Thread

Runs On (thread)

Main Thread

Its own thread

Separate worker thread

Worker thread. However, Main thread methods may be invoked in between to publish progress.

Limitations /
Drawbacks

May block main thread

- Manual thread management

- Code may become difficult to read

- Cannot run tasks in parallel.

- Multiple intents are queued on the same worker thread.

- one instance can only be executed once (hence cannot run in a loop) 

- Must be created and executed from the Main thread