1    /* 
2    Creating a program that carries an array with the first 4 prime numbers. 
3    Asking JAVA to give us the first element, last element, and have them switch. 
4     */
5    
6    package arraylistplay;
7    
8    import java.util.ArrayList;
9    
10   public class Primes {
11       public static void main(String[] args) {
12           ArrayList<Integer> primes = new ArrayList<>();
13           primes.add(2); // add an integer, 2, at the end of the array list.
14           primes.add(3); // add an integer, 3, after the integer 2 in the array list.
15           primes.add(5);
16           primes.add(7);
17   
18           System.out.println("size of primes list = " + primes.size());
19   
20           // primes.get(x) means to get me the integer whose index is x.
21           System.out.println("first prime = " + primes.get(0));
22           System.out.println("last prime = " + primes.get(3));
23           System.out.println("last prime = " + primes.get(primes.size() -1));
24   
25           System.out.println("\nThe initial list . . .");
26           for ( Integer prime : primes ) {
27               System.out.println(prime);
28           }
29   
30           int temp = primes.get(0);
31           primes.set(0, primes.get(primes.size() - 1)); // replace index zero with the last integer.
32           primes.set(primes.size()-1, temp); // replace the last integer with the first one.
33   
34           System.out.println("\nThe final list . . .");
35           for (Integer prime : primes) {
36               System.out.println(prime);
37           }
38       }
39   }
40