Java text classification problem [closed]

Answer 1

Do you not want something as simple as this?

Map> m = {};
for (Book b : books) {
    for (tag t : b.taglist) {
        m.get(t).add(b);
    }
}

Now m.get("IT") will return all IT books, etc...

Sure some books will appear in multiple categories, but that happens in real life, too...