what is api and its advantages code example

Example: advantages of api

1-We can start testing process 
EARLY and the more bugs we
catch in API level testing,
the less bugs we will see on UI.
API level of application is
developed before the UI part.

2- API tests enable highly 
integrable tests, which is 
particularly useful if you
want to perform functional
GUI tests after API testing. 

3-In API testing,
data is exchanged
using XML or JSON.

4- Time Effective:
API testing usually is less time consuming
than functional GUI testing.