I want to have an array of ArrayLists:
ArrayList<MyClass>[] myArray;
I want to initialize it by the following code:
myArray = new ArrayList<MyClass>[2];
But I get this error:
Cannot create a generic array of ArrayList<MyClass>
How can I initialize it?
This is not strictly possible in Java and hasn't been since its implementation.
You can work around it like so:
ArrayList<MyClass>[] lists = (ArrayList<MyClass>[])new ArrayList[2];
This may (really, it should) generate a warning, but there is no other way to get around it. In all honesty, you would be better off to create an ArrayList of ArrayLists:
ArrayList<ArrayList<MyClass>> lists = new ArrayList<ArrayList<MyClass>>(2);
The latter is what I would recommend.
List<E> instead of arrays when dealing with generics.As arrays are static in nature and resolved in compile time so you cannot do that instead you can use ArrayList. As
ArrayList<ArrayList<MyClass>>
How about this?
ArrayList<String>[] f = (ArrayList<String>[]) Array.newInstance(ArrayList.class, size);
for(int ix = 0; ix < f.length;ix++)
f[ix] = new ArrayList<String>();
Array.newInstance(ArrayList.class, size) has no advantage over new ArrayList[size]. There is never a point in using Array.newInstance with a class literalYou can use
HashMap<some key,ArrayList<MyClass>> or ArrayList<ArrayList<MyClass>>
ArrayList<ArrayList<MyClass>>new ArrayList<MyClass>[2];tonew ArrayList[2];it will work but you will get warning. Not that I am recommending it though.