java - Server Client Communication -

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i want know.. suppose there website or mobile app. whatsapp or hangout. when ever receive new message :

  1. if app in foreground see on list. else notification.

  2. now want know.. fetch messages app/ website have poll server.

is way, server tells app/wesite have fetch data?

and connection between these 2 points.?? can me understand how work.. , how achieve point 2.

just give brief idea.

i think after broadcastreceiver class.

a simple intent-filter receiver in androidmanifest file can take care of notification part.


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