Nā Kai ʻEwalu is an excellent book for learning the Hawaiian language as it explains the rules of the langauge in the style of Hawaiian language structure and using Hawaiian words. The first year book has been recently revised and enlarged and comes in two sections; there is also an older book for second year, as follows:

Textbook 1: Chapters 1-14 (Hawaiian Language Year 1) 

Textbook 2: Chapters 15-27 (Hawaiian Language Year 2)