Question

Sorry for the silly question, but I cannot seem to find an answer on google. I have written a class, and within the class there is a constructor which creates an arraylist, in the same class there is a method which iterates through the array list by creating an iterator object. As my code stands, however, it is not recognizing the arraylists name, should I store the array list in a class variable, or pass it into the method as an argument ?

What is usually best practice here as this is something that is always getting me ?

My code is as follows if you can’t follow my somewhat convuluted explanation ! Apologies ! Thanks a lot for reading 🙂

import java.util.*;
public class Primes {
  public Primes( int initialCapacity) {
    ArrayList<Integer> listOfPrimeNumbers = new ArrayList<Integer>(initialCapacity);    
    //how do I get the above...
    int index = 2;
    while (index != listOfPrimeNumbers.size())
    {
      if (isPrime(index))
      {
        listOfPrimeNumbers.add(index);  
      }
      index++;
    }
  }
  public static boolean isPrime(int candidateNo) {
    Iterator<Integer> iter = listOfPrimeNumbers.iterator( );
    //in here ! ?
    i=2;
    while ( iter.hasNext( ) ) {
      if (candidateNo%i==0 && i!=1) {
        return false;
      }
      else
        return true;
    }
  }

(Also, if you see anything horrifically wrong with my code please don’t be afraid to call me out on it, the more constructive criticism the better!)
}

Answer 1

You define a private var for your ArrayList and initalize this variable in your Constructor.
Now you can access the list inside your Class 🙂
hope that helps.

import java.util.*;
public class Primes {

  private ArrayList<Integer> listOfPrimeNumbers;

  public Primes( int initialCapacity) {
    listOfPrimeNumbers = new ArrayList<Integer>(initialCapacity);    
    //how do I get the above...
    int index = 2;
    while (index != listOfPrimeNumbers.size())
    {
      if (isPrime(index))
      {
        listOfPrimeNumbers.add(index);  
      }
      index++;
    }
  }
  public static boolean isPrime(int candidateNo) {
    Iterator<Integer> iter = listOfPrimeNumbers.iterator( );
    //in here ! ?
    i=2;
    while ( iter.hasNext( ) ) {
      if (candidateNo%i==0 && i!=1) {
        return false;
      }
      else
        return true;
    }
  }