what does the arguments of startelement() method in SAX parser refer to

public void startElement(String uri, String localName, String qName,
             Attributes attributes)
 

can anybody please give a simple example as to how localname is different from qName and what exactly is the uri string ? And yes before somebody asks I did check it on the net but no one cared to mention the difference as some examples used qName and others used localname which is really confusing for me.

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