in the end意思是 终于,最后.是一个句子成分,修饰整个句子如：in the end,it was more than he could bear(最后,他再也忍不住了）
by the end of ...意为:到.为止(常与完成时态连用注:不一定非要将来的完成不可,还可和过去完成时呀现在完成时连用)
at the end (of...可省略)在(...的)未端:在(...后期)
by the end of this year,they will have finished work on the new stadium(在今年年底工人们很把路铺好）注：have+过去分词表将来完成时
by表：在某时之前,并不晚于某时的任何时间.只能与时间点的名词或词组连用.在肯定与否定句中有区别
i will have left by monday到星期一我将离开（星期一之前的任何时间）
i will not have left by monday 我星期一之前不会离开的.（我星期一还在这）