Best practice for getters and setters for collection properties and object properties in a java class

Question

i have the following implementation

public class PartGroup {

   private Part iPart;

   private ArrayList<Part> iParttList;

   public Part getPart() {
      return iPart;
   }

   public void setPart( Part aPart ) {
      iPart = aPart;
   }


   public ArrayList<Part> getParttList() {
      return iParttList;
   }


   public void setParttList( ArrayList<Part> aParttList ) {
      iParttList = aParttList;
   }

}

Is it ok to have setters for iParttList and iPart ? i think it is safe to have a getter only then the consumer can use getter to get the created instance of the collection and clear or add elements to the collection should i remove the setter and add the following implementation

public ArrayList<Part> getParttList() {
      if(iParttList == null)
         iParttList = new ArrayList<Part>();

      return iParttList;
   } 

public Part getPart() {
       if(iPart == null)
          iPart = new Part();

       return iPart;
   }

What is the best practice?

Answer 1

The second implementation guards against returning null, right? So if there's a chance this object could return null (because what constructors there are permit this or it otherwise could come to pass) and that would be a Bad Thing for your intended use case, then use the second implementation.