Using a long as ArrayList index in java

Question

I am writing this java program to find all the prime numbers up to num using the Sieve of Eratosthenes, but when I try to compile, it says I can\'t use a long var as an arra

Answer 1

I'm not sure why your code would compile to begin with.

You're not supposed to use [] in an array list to access members. An arraylist is merely a list that is internally stored in an array. You have to use the list get operation (which would still be O(1)). Writing numlist[index] means that you have an array of objects in numlist. You cannot override the [] operation as in C++.

In addition, an int is 32 bits in Java. Having an array of length greater than 2^32 (so you would need long indices) is unlikely and I'm not even sure the specification allows it.