Try this link.
And if you still cannot figure it out then let us know.

Sir,
the letmegoogleit.com was excellent.
thanks for telling me that I can do that.
but,I have found this but it still doesnt clear my doubt

the asking program uses a set of standardized requests, called application programming interfaces (API), that have been defined for the program being called upon. Almost every application depends on the APIs of the underlying operating system to perform such basic functions as accessing the file system. In essence, a program's API defines the proper way for a developer to request services from that program.

Does this mean that if i use methods like nextToken() from StringTokenizer,or I can call my class an API as someone can use it in his program.

IT depends on if your program has something to offer for others. An API offers an abstraction for some low-level tasks while doing some higher level tasks. Let me give you an example of address book itself (since your program dela with it) An address book has contacts which can be created, edited and deleted. Further more it is also supposed to offer functionality such as searching of a contact. Now if you write a collection of classes that provide this basic functionality like say you store contact's using a List and implement the create, edit, delete and search functions. Meaning you provide the most general address book operations through your classes so that developers, using your library, might be able to implement an AddressBook feature without worrying about the details of create, edit and delete (they just call your functions) then you might be able to say that you have provided an API for an AddressBook.

Now deciding whether your program is an API or not is pretty straight forward.

Thanks a million sir.
Shubhang Sharma,
Goa.

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