Question

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Java how to: Generic Array creation
Error: Generic Array Creation

I am getting this error:

Cannot create a generic array of T

This is my code (error on line 6):

1    public class HashTable<T> {
2    
3        private T[] array;
4    
5        HashTable(int initSize) {
6            this.array = new T[initSize];
7        }
8    }

I am wondering why this error is appearing and the best solution to fix it. Thanks.

UPDATE:

I adjusted my code so that the array is taking in linked lists instead, but I am getting a new error.

Here is my error:

Cannot create a generic array of LinkedList<T>

Here is my code (error on line six):

1    public class HashTable<T> {
2    
3        private LinkedList<T>[] array;
4    
5        HashTable(int initSize) {
6            this.array = new LinkedList<T>[initSize];
7        }
8    }

Is this error for the exact same reason? I was just assuming I could create generic linked lists and just store them in the array.

Answer 1

Generic arrays can be created via reflection (although an unsafe cast is required), you just need to pass the class as a parameter (assuming that the following method is inside a class that defines a <T> type parameter):

@SuppressWarnings("unchecked")
public T[] createArray(Class<T> klass, int size) {
    return (T[]) Array.newInstance(klass, size);
}

For example, in your case:

HashTable<Integer> t = new HashTable<Integer>();
Integer[] intArray = t.createArray(Integer.class, 4);
intArray[0] = 1; intArray[1] = 2;
intArray[2] = 3; intArray[3] = 4;

System.out.println(Arrays.toString(intArray));
> [1, 2, 3, 4]