[ja] Apply 51ba3fa4cc2fb203f8c377d5a937bf5f3425526d and fix typo
[ja] Apply b294744d98a6f6cdbc3508b0058f8616147c1596
[ja] Apply 8ec0ce6bfcd7944193a95a4794bf2cc88e874362
Merge pull request #415 from harupong/ja-chapter7

[ja] Update chapter7