In 30 years I will have been working for 45 years. By the time I retire, I will have been a teacher of 3 generations of kids. In 2 days, the bug will have been eaten by the frog In 100 years, gasoline powered vehicles will have been replaced by electric vehicles. In a week, the groceries I bought will have been consumed.

"Will have been verb+ing" is the past of the future (Future perfect continuous). It describes something that will have been continuing up to time yet to come. It is often accompanied by phrases like: by the time, for, since, the last few hours, by the end, etc. By the time I get to Phoenix, I will have been driving nine hours. By the year 2020, people will have been using non-biodegradable plastic for eighty years.