Can we have an Array of a collection?

Question

I was trying create an array of a collection as follows.

ArrayList<Integer> ar[]=new ArrayList<Integer>[50];

but it gives me an error -> generic array creation can anybody explain me why is it?

Answer 1

You can't create arrays of generic types. Use collection of collections instead:

ArrayList<ArrayList<Integer>> = new ArrayList<ArrayList<Integer>>();

Why can't we create an array of generic type? Array stores they exact type internally, but due to the type erasure at runtime there will be no generic type. So, to prevent you from been fooled by this (see example below) you can't create an array of generic type:

//THIS CODE WILL NOT COMPILE
ArrayList<Integer>[] arr = new ArrayList<Integer>[5];
Object[] obj = arr;
obj[0] = new ArrayList<Long>(); //no one is safe