Examples using ArrayList and generics

"How about I start with what's actually useful? You'll now see a couple of ways that ArrayList and generics can be put to work:"

"Example 1:"

public static void main(String[] args) throws IOException
 {
     BufferedReader reader = new BufferedReader(new InputStreamReader(System.in) );
     ArrayList<Integer> list = new ArrayList<Integer>() ;

     while (true)
     {
         String s = reader.readLine();
         if (s.isEmpty()) break;
         list.add(Integer.parseInt(s));
     }
 }

"Example 2:"

public static void main(String[] args) throws IOException
 {
     BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
     ArrayList<Integer> list = new ArrayList<Integer>();

     while (true)
     {
         String s = reader.readLine();
         if (s.isEmpty()) break;

         int x = Integer.parseInt(s);
         if (x % 2 == 0)  // Check that the remainder is zero when we divide by two
             list.add(x);         // Add to the end
         else
             list.add(0, x);      // Add to the beginning
     }
 }

"Example 3:"

public static void main(String[] args) throws IOException
 {
     BufferedReader reader = new BufferedReader(new InputStreamReader(System.in) );
     ArrayList<Integer> list = new ArrayList<Integer>();

     list.add(1);
     list.add(7);
     list.add(11);
     list.add(3);
     list.add(15);

     for (int i = 0; i < list.size(); ) // We moved the statement that increases i to inside the loop
     {
         if (list.get(i) > 5)
             list.remove(i);  // Don’t increase i if we deleted the current element
         else
             i++;
     }
 }

"Example 4:"

public static void main(String[] args) throws IOException
 {
     // Static initialization of the array
     int[] data = {1, 5, 6, 11, 3, 15, 7, 8};

     // Create a list where all elements are Integers
     ArrayList&ltInteger> list = new ArrayList&ltInteger> ();

     // Use the array to fill the list
     for (int i = 0; i < data.length; i++) list.add(data[i]);

     ArrayList&ltInteger> even = new ArrayList&ltInteger>();  // Even numbers
     ArrayList&ltInteger> odd = new ArrayList&ltInteger>();    // Odd numbers

     for (int i = 0; i < list.size(); i++)
     {
         Integer x = list.get(i);
         if (x % 2 == 0)    // If x is even
             even.add(x);   // Add x to the collection of even numbers
         else
             odd.add(x);    // Add x to the collection of odd numbers
     }
 }

"Example 5:"

public static void main(String[] args) throws IOException
 {
     ArrayList<Integer> list1 = new ArrayList<Integer>();   // Create a list
     Collections.addAll(list1, 1, 5, 6, 11, 3, 15, 7, 8);   // Fill the list

     ArrayList<Integer> list2 = new ArrayList<Integer>();
     Collections.addAll(list2, 1, 8, 6, 21, 53, 5, 67, 18);

     ArrayList<Integer> result = new ArrayList<Integer>();

     result.addAll(list1);   // Add all values from each list to the new list
     result.addAll(list2);

     for (Integer x : result)   // A fast way to loop over all elements, only for collections
     {
         System.out.println(x);
     }
 }

"Cool! Will Diego now give me a truck load of similar exercises?"

"Yes, he will."