Tags in tiddlywiki can be also tiddlers. Eg: you can create a tiddler named: java that contains the following content:
Then you create a second tiddler named: Java ... with the content
The second tiddler is there, just to be sure you can use [[java]] and [[Java]] as links to the tag-tiddler.
The advantage of this mechanism is, that you can decide, which "java" words link to the tag-tiddler. .. If every occurrence of the "java" text will link to the tag-tiddler, for me personally it would be annoying to have 10 links in a text, that all link to the same target.
You can add this to your java-tag tiddler.
Backlinks: <$list filter="[[java]backlinks] [[Java]backlinks]"><<currentTiddler>>, </$list>
Which will show you, where your links to [[java]] come from.