Hello)future perfect tense is used when you want to express that the action will be done by the exact moment(E.g. i will finish my job tomorrow-Future simple tense; I will have finished my job BY tomorrow-Future perfect tense) (I will do my homework tomorrow-Future simple tense; i will have done my homework BY 5 oclock tomorrow) so we use Future perfect tense whe we want to underline that the action will be done BY exact moment in the future!!!

将来完成时 1） 构成will have done 2） 概念 a. 状态完成：表示某事继续到将来某一时为止一直有的状态。例如： They will have been married for 20 years by then. 到那时他们结婚将有二十年了。 b. 动作完成：表示将来某一时或另一个将来的动作之前，已经完成的动作或获得的经验。例如： You will have reached Shanghai by this time tomorrow. 明天此时，你已经到达上海了。