"generic array creation" when fixing complains about unsafe operation

Question

The following line of code causes javac to give an unsafe operation warning:

LinkedList<Node>[] buckets = new LinkedList[bucketCount];

However, when I try to fix that by doing this:

LinkedList<Node>[] buckets = new LinkedList<Node>[bucketCount];

I get a generic array creation error. How can I solve this?

@NPE I'm implementing my own hashmap for educational purposes. — Overv, Mar 22 '13 at 10:26
I believe the syntax is List buckets = new LinkedList(bucketCount); — Gilbert Le Blanc, Mar 22 '13 at 10:26
@NPE That was a typo, the type on the left is definitely an array. — Overv, Mar 22 '13 at 10:31
There might be some good background information at http://stackoverflow.com/questions/2927391/whats-the-reason-i-cant-create-generic-array-types-in-java — Andreas Fester, Mar 22 '13 at 10:32

score 1 · Accepted Answer · edited May 23 '17 at 11:43

1

In a nutshell, arrays of generic types are problematic.

Turn buckets into an ArrayList of LinkedLists:

ArrayList<LinkedList<Node>> buckets = new ArrayList<LinkedList<Node>>(bucketCount);
for (int i = 0; i < bucketCount; ++i) {
    buckets.add(new LinkedList<Node>());
}

This way you'll get compile-time type safety.

edited May 23 '17 at 11:43

Community

1
1

answered Mar 22 '13 at 10:29

NPE

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Yeah, Java generics are kinda a hack, and don't handle this situation well. But it's silly to have to go to using a non-array to circumvent an artificial restriction. – Hot Licks Mar 23 '13 at 02:07

Hunter Zhao · Answer 2 · 2013-03-23T01:53:05.687

LinkedList only has two constructors, one is default, and the other accepts a parameter which extends Collection,

public LinkedList(Collection<? extends E> c) {
this();
addAll(c);
}

this is to say that LinkedList cann't have a initialization size, if it's nessary to initialize the capacity of container, you'd better use ArrayList, like following:

List<Node> list = new ArrayList<Node>(bucketCount);

Good luck :)

"generic array creation" when fixing complains about unsafe operation

2 Answers2