This is a proper way to create an array:
@SuppressWarnings("unchecked") LinkedList<Long> [] hashtable = new LinkedList[10];
Cannot Create Arrays of Parameterized Types
You cannot create arrays of parameterized types. For example, the following code does not compile:
List<Integer>[] arrayOfLists = new List<Integer>[2]; // compile-time error
The following code illustrates what happens when different types are inserted into an array:
Object[] strings = new String[2];
strings[0] = "hi"; // OK
strings[1] = 100; // An ArrayStoreException is thrown.
If you try the same thing with a generic list, there would be a problem:
Object[] stringLists = new List<String>[]; // compiler error, but pretend it's allowed
stringLists[0] = new ArrayList<String>(); // OK
stringLists[1] = new ArrayList<Integer>(); // An ArrayStoreException should be thrown,
// but the runtime can't detect it.
If arrays of parameterized lists were allowed, the previous code would fail to throw the desired ArrayStoreException
.
Taken from docs.oracle.com
So what can I store in hashtable[] ?
Does it mean I am now allowed to have a linked list of string in the
hashtable[0] and a linked list of Long in hashtable1, if I do
LinkedList [] hashtable = new LinkedList[10]?
No, compiler won't allow you to store LinkedList to the hashtable array directly. Following snippet won't compile:
hashtable[0] = new LinkedList<String>();
However you can store the LinkedList without type parameters, or even a subclass of LinkedList:
@SuppressWarnings("unchecked") LinkedList<Long>[] hashtable = new LinkedList[10];
hashtable[0] = new LinkedList<Long>();
hashtable[1] = new MyLinkedList<Long>();
hashtable[2] = new LinkedList();
hashtable[3] = new MyLinkedList();
You can store the LinkedList if you cast your array to LinkedList[]. However you won't be able to store the anything else but a LinkedList:
LinkedList[] rawHashTable = hashtable;
rawHashTable[4] = new LinkedList<String>();
Object[] objectHashTable = rawHashTable;
objectHashTable[5] = "This line will throw an ArrayStoreException ";