Future接口和FutureTask类【FutureTask实现了Runnable和Future接口】
API:Java代码publicinterfaceFuture{/***Attemptstocancelexecutionofthistask.Thisattemptwill*failifthetaskhasalreadycompleted,hasalreadybeencancelled,*orcouldnotbecancelledforsomeotherreason.Ifsuccessful,*