类强制转换异常和泛型（java）

Question

I am implementing my own priority queue and using a class called sportsball that uses it. The priority queue is based on generics and uses a Node (T object, int value) (aka Name of player and their score). I am getting a class cast exception error when I try to run the program.

Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [LPriorityQueue$Node;
    at PriorityQueue.<init>(PriorityQueue.java:35)
    at sportsball.main(sportsball.java:48) 

The lines in question are: PriorityQueue.java:35:

Node[] array = (Node[])(new Object[initialSize]);

sportsball.java:48:

PriorityQueue<String> queue = new PriorityQueue<String>(start, step);

Thank you for your help!

Note:

When I tried having line PriorityQueue.java:35:

Node[] array = new Node[initialSize];

the error: generic array creation pops up instead.

Answer 1

You cannot cast an Object to a Node , so you shouldn't be able to cast an Object[] to a Node[] . Just create the Node[] directly.

Node[] array = new Node[initialSize];

Answer 2

You cannot cast object to the Node as you did

Node[] array = (Node[])(new Object[initialSize]);

hence the exception ClassCastException: [Ljava.lang.Object; cannot be cast to [LPriorityQueue$Node ClassCastException: [Ljava.lang.Object; cannot be cast to [LPriorityQueue$Node which is clear that object cannot be castable to Node Type

So you can go with this option

Node[] array = new Node[initialSize];

Answer 3

You cannot simply cast an Object[] to a Node[]. This will indeed generate a ClassCastException. Just create a Node[] instead ( Node[] array = new Node[initialSize]; ). Without more code than this, I cannot say anything else about it.

Note that the message of the ClassCastException is already indicating the problem. [Ljava.lang.Object; refers to Object[] and similarly, [LPriorityQueue$Node; refers to Node[] .