Groovy
Retrieve the first object (index [0]) among all objects attached to this page and of a certain class
obj = doc.getObject('XWiki.XWikiComments')
com.xpn.xwiki.api.Object@100849df
Retrieve all objects attached to this page and of a certain class and one of their properties
objs = doc.getObjects('XWiki.XWikiComments')
[com.xpn.xwiki.api.Object@75184dff, com.xpn.xwiki.api.Object@ea8dc68, com.xpn.xwiki.api.Object@701e375c, com.xpn.xwiki.api.Object@4fc4b285, com.xpn.xwiki.api.Object@7aa462ac, com.xpn.xwiki.api.Object@3e4a491b, com.xpn.xwiki.api.Object@7f05ab8f, com.xpn.xwiki.api.Object@4d427a6f, com.xpn.xwiki.api.Object@47743509]
objsAuthors = doc.getObjects('XWiki.XWikiComments').author
objsAuthor = doc.getObjects('XWiki.XWikiComments')[2].author
println objs[0].author
println objsAuthors
println objsAuthor