FixedThreadPool和CachedThreadPool之间的区别

Question

FixedThreadPool有什么区别，可以用作风箱：

ExecutorService ex = Executors.newFixedThreadPool();

和CachedThreadPool：

ExecutorService ex = Executors.newCachedThreadPool();

在CompletableFuture上：

CompletableFuture<Integer> promise = CompletableFuture.supplyAsync(()->{.........}, ex);