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@6cfa6746
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@63579082, com.xpn.xwiki.api.Object@9d079c2, com.xpn.xwiki.api.Object@55e9b496, com.xpn.xwiki.api.Object@624f0fea, com.xpn.xwiki.api.Object@349dfe12, com.xpn.xwiki.api.Object@70936aba, com.xpn.xwiki.api.Object@5e441313, com.xpn.xwiki.api.Object@474074be, com.xpn.xwiki.api.Object@58b08a7d]
objsAuthors = doc.getObjects('XWiki.XWikiComments').author
objsAuthor = doc.getObjects('XWiki.XWikiComments')[2].author
println objs[0].author
println objsAuthors
println objsAuthor