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@7e941c6b
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@71e1ecb6, com.xpn.xwiki.api.Object@277bdb23, com.xpn.xwiki.api.Object@346feb15, com.xpn.xwiki.api.Object@1fb2ca98, com.xpn.xwiki.api.Object@1312d16a, com.xpn.xwiki.api.Object@38728fee, com.xpn.xwiki.api.Object@69476f35, com.xpn.xwiki.api.Object@50d63692, com.xpn.xwiki.api.Object@1f98d4b4]
objsAuthors = doc.getObjects('XWiki.XWikiComments').author
objsAuthor = doc.getObjects('XWiki.XWikiComments')[2].author
println objs[0].author
println objsAuthors
println objsAuthor