java - why does this code output "0"? -

package algorithms; import cs1.keyboard; import java.util.*;  public class sieveoferatosthenes2 {     public static void main (string[] args){          //input number , create array length of (num-1)         int num = keyboard.readint();         arraylist prime = new arraylist(num);          //populate array numbers 2 num         for(int = 0; < prime.size()-1; i++)         {             integer temp = new integer(i+2);             prime.add(i, temp);         }         system.out.println(prime.size()); 

the constructor here doesn't set size of arraylist num, sets capacity num:

arraylist prime = new arraylist(num); 

the size of arraylist still zero, loop body never runs. try instead:

for (int = 0; < num - 1; i++) {     integer temp = new integer(i+2);     prime.add(temp); } 

definition of size:

the number of elements in list.

definition of capacity:

each arraylist instance has capacity. capacity size of array used store elements in list. @ least large list size. elements added arraylist, capacity grows automatically. details of growth policy not specified beyond fact adding element has constant amortized time cost.