Question

Let’s say I have a class A that has a list of related elements (type of elements not relevant):

public class A {
  private List<String> list;

  public List<String> getList() {
    return list;
  }

  public void addElement(String element) {
    list.add(element);
  }
}

Now I want access to this list from another class, Client. I need to add a new element. The question, a more phylosophical one, is how best is this done from a design point of view.

public class Client {
  private A a = new A();

  public void method1() {
    a.getList().add("");
  }

  public void method2() {
    a.addElement("");
  }    
}

If anyone could point out any advantage of any of these methods, would be much appreciated.
Thanks.

Answer 1

Generally your getList() method is considered bad style. If class A returns a reference to its actual List, than a caller might call clear() on that list, or add a million elements to it, or so who-knows-what-all. It’s a much better idea to return only an Iterator, or only a read-only view of the List using Collections.unmodifiableList().

This means your solution 2, addElement() is better; the addElement() method might contain code to validate the added elements, limit the size of the list, or whatever. And clear() would not be accessible.