为什么我不能输入：BlockingQueue<Integer> a = 新的 PriorityQueue&lt;&gt;(2);

Question

The code I type in title doesn't compile. It says: Cannot infer arguments .

After that I did BlockingQueue<Integer> a = new PriorityBlockingQueue<>(2); which compiles just fine. What was my mistake, so I can avoid it next time?

Yes, I know that constructor in Queue interface has parameter(2) for initial capacity , while in BlockingQueue parameter(2) represents max elements . Does this have anything to do with the error ?

Answer 1

Well for starters, PriorityQueue is not a BlockingQueue . It wont be able to infer any generic arguments for PriorityQueue<T> because there is no T that will be valid. That being said, Cannot infer arguments sounds like it may be due to a side effect of this change somewhere else in your code.

Looking at the documentation for BlockingQueue , you should instead use one of the classes under "All Known Implementing Classes:", find a library with BlockingQueue s, or implement your own.

Your other option is to use another type of queue instead, like AbstractQueue<Integer> in place of BlockingQueue<Integer> .

Answer 2

The code in the title doesn't compile because PriorityQueue does not implement nor extend BlockingQueue . It's like doing this: LinkedList<Integer> ls = new ArrayList<>(): , which will not compile.