1. import java.util.ArrayList;
  2. import java.util.Iterator;
  3.  
  4. /**
  5.  * Some exercises to practice the concepts of looping and arraylists
  6.  * 
  7.  * Looping through multiples of 5 between 10 and 95
  8.  * Adding up all numbers between 2 integers
  9.  * Testing if a number is a prime
  10.  * 
  11.  * @author Justin Chan
  12.  * @version v.1
  13.  */
  14. public class Looptester
  15. {
  16.     private ArrayList<Integer> modValues;
  17.     private int[] modValues2;
  18.  
  19.     /**
  20.      * Constructor for objects of class tester
  21.      */
  22.     public Looptester()
  23.     {   
  24.         modValues = new ArrayList<Integer>();
  25.     }
  26.  
  27.     /**
  28.      * Tests is a number is a prime using an Array
  29.      * 
  30.      * @return True if it is a prime, false if it is not
  31.      * @param n The number whose status as a prime number you wish to find out
  32.      */
  33.     public boolean arrayPrime(int n)
  34.     {
  35.         modValues2 = new int[n - 2];
  36.         int nextIndexNumber = 0;
  37.         boolean hasZero = true;
  38.  
  39.         //x is the divisor, goes from 2 to n-1 inclusive
  40.         for(int x = n - 1; x > 1 ; x--)
  41.         {
  42.             //x value loops through all numbers between 1 and n-1
  43.             modValues2[nextIndexNumber] = (n % x);
  44.             nextIndexNumber++;
  45.         }
  46.  
  47.         for(int modValue : modValues2)
  48.         {
  49.             if(modValue != 0)
  50.             {
  51.                 //there are no 0s in the Array
  52.                 //it is a prime
  53.                 hasZero = true;
  54.             }
  55.  
  56.             else
  57.             {
  58.                 //there is a 0 in the Array
  59.                 //it is not a prime
  60.                 hasZero = false;
  61.             }
  62.         }     
  63.         //empty Array for subsequent method calls
  64.         modValues2 = new int[n]; 
  65.         return hasZero;
  66.     }
  67.  
  68.     /**
  69.      * Tests is a number is a prime using a for-loop
  70.      * 
  71.      * @return True if it is a prime, false if it is not
  72.      * @param n The number whose status as a prime number you wish to find out
  73.      */
  74.     public boolean isPrime(int n)
  75.     {
  76.         boolean isPrime = true;
  77.  
  78.         for(int i = 2; i < n; i++)
  79.         {
  80.             if(n % i == 0)
  81.             {
  82.                 isPrime = false;
  83.                 //break;
  84.             }
  85.         }
  86.         return isPrime;
  87.     }
  88.  
  89.     /**
  90.      * Tests is a number is a prime using an ArrayList
  91.      * 
  92.      * @return True if it is a prime, false if it is not
  93.      * @param n The number whose status as a prime number you wish to find out
  94.      */
  95.     public boolean arrayListPrime(int n)
  96.     {
  97.         int x = n; //x is the divisor, goes from 2 to n-1 inclusive
  98.  
  99.         while(x > 2)
  100.         {
  101.             x--; //x value loops through all numbers between 1 and n-1
  102.             modValues.add(n % x);
  103.         }
  104.  
  105.         if(modValues.contains(0) == false) //can't find a 0 in modValues, is prime
  106.         {
  107.             //empties array
  108.             modValues = new ArrayList<Integer>();
  109.  
  110.             return true;
  111.         }
  112.  
  113.         else //there is a 0 in modValues, is prime
  114.         {       
  115.             //empties array
  116.             modValues = new ArrayList<Integer>();
  117.  
  118.             return false;   
  119.         }
  120.     }
  121. }