[ja] Apply 60c632a9f30b7c2266b9dad400e2fba576366280
[ja] Apply a96c65b9ac03762693af2d12337b032575495ae5
[ja] Apply bc3f922f2549e44524dc11301d1e53c984b14a1b
Merge pull request #412 from harupong/ja-chapter6

[ja] Update chapter6