Linked Lists - Building Java Programs: A Back to Basics Approach - page 961

You can introduce an interface with just the method headers to capture this notion
of the integer list:
1 public interface IntList {
2 public int size();
3 public int get( int index);
4 public String toString();
5 public int indexOf( int value);
6 public void add( int value);
7 public void add( int index, int value);
8 public void remove( int index);
9 }
Using the interface, you can write a processList method to use in the client
program:
1 public class ListClient2 {
2 public static void main(String[] args) {
3 ArrayIntList list1 = new ArrayIntList();
4 processList(list1);
5
6 LinkedIntList list2 = new LinkedIntList();
7 processList(list2);
8 }
9
10 public static void processList(IntList list) {
11 list.add(18);
12 list.add(27);
13 list.add(93);
14 System.out.println(list);
15 list.remove(1);
16 System.out.println(list);
17 }
18 }
If this is the only change you make, then your program will include two errors
instead of one. Now both calls on the method cause an error. That seems a bit odd,
because both ArrayIntList and LinkedIntList have the methods mentioned in the
IntList interface. But recall that Java requires classes to explicitly state which inter-
faces they implement. So you have to modify the two classes to include this notation:
public class ArrayIntList implements IntList {
...
}