Barcode reading in Java

Hi Everybody I am an MCA student.
I want to know how does the bar code reaer works and How we can use it
in a poject where we can take input by reading the bar code and
display the information about the item.
like in malls they just read the barcode and all the info comes there?
Which tool to use?
I am a fresher and want to implement this in project.
Thank U
Pankaj

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