Containers

A container is an object that contains 0 or more other objects.

The container manages a collection such as a set, list, or array:

class Company {
   private List<Employee> staff = new ArrayList<Employee>();
   public void hire(Employee e) {
      staff.add(e);
   }
   public void fire(Employee e) {
      staff.remove(e);
   }
   public int find(Employee e) {
      return staff.indexOf(e);
   }
   public Employee get(int i) {
      return staff.get(i);
   }
   public int size() {
      return staff.size();
   }
}

Note the management methods provided by the container include methods for adding, removing, and fetching members.

Here's a text harness:

class TestCompany {
   public static void main(String[] args) {
      Company acme = new Company();
      acme.hire(new Manager());
      acme.hire(new Programmer());
      acme.hire(new Employee());

      for(int i = 0; i < acme.size(); i++) {
         acme.get(i).getToWork();
      }
   }
}

Here's the output produced:

fire somebody
fix bugs
look busy