Java ClassCastException confusion

Question

I have the following code:

PriorityQueue<Pair<Integer, Double>> pq = 
      new PriorityQueue<>((v1, v2) -> (int)Math.floor(v1.getValue() - v2.getValue()));
pq.add(new Pair(1, 0));
Pair<Integer, Double> node = pq.poll();
double time = node.getValue();

The last line raises a

java.lang.ClassCastException: class java.lang.Integer cannot be cast to class
java.lang.Double (java.lang.Integer and java.lang.Double are in module 
java.base of loader 'bootstrap')

The issue goes away if I replace the second statement with

pq.add(new Pair(1, 0.0));

I'd like to understand what is happening under the hood resulting in this exception.

What is Pair? Is that a standard class?

markspace
– markspace

2022-05-15 20:59:25 +00:00
Commented May 15, 2022 at 20:59 — markspace
– markspace, Commented May 15, 2022 at 20:59

Dawood ibn Kareem · Accepted Answer · 2022-05-15 21:04:30Z

2

An int can be cast to a double, but an Integer can't be cast to a Double.

When you instantiate your Pair<Integer, Double>, both int values that you're passing are getting autoboxed to Integer. But what you needed was an Integer and a Double.

answered May 15, 2022 at 21:04

Dawood ibn Kareem

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1 Comment

markspace Over a year ago

I think the OP is expecting that the declaration PriorityQueue<Pair<Integer, Double>> will force the int to a Double when new Pair is executed. But I'm not 100% sure that's what they're asking about either.

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