What are these API's?

i'm new to android and i would开发者_Go百科 like to know about these api's..

wen i was browsing the developers guide i found out some thing like Api 1,Api 2,Api 7......etc

what are these Api's and the purpose of their presence.....

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Each API # corresponds to different Adnroid/Android SDK version:

• Api 3 - Android 1.5
• Api 4 - Android 1.6
• etc

Read more about API levels at official documentation.