Sample init.el for this Reddit discussion https://www.reddit.com/r/emacs/comments/54pvg4/usepackage_with_builtin_modes/

init-for-reddit.el

(require 'package)
(setq package-enable-at-startup nil)
(dolist (archive '(("melpa-stable" . "http://stable.melpa.org/packages/")
		   ("melpa" . "http://melpa.org/packages/")))
  (add-to-list 'package-archives archive :append))
(package-initialize)

(unless (package-installed-p 'use-package)
  (package-refresh-contents)
  (package-install 'use-package))

(use-package java-mode
  :commands java-mode
  :init
  (add-hook 'java-mode-hook #'subword-mode))