Question

Lets say I have the following code:

public class Collection implements CollectionInterface{

 ElementInterface[] elementArray = new ElementInterface[100];
 int amountOfElements = 0;

 public Collection()
 {

 }

 public Collection(CollectionInterface collection)
 {
  CollectionInterface tempCollection = new Collection();
  while(!collection.isEmpty())
  {
   ElementInterface element = collection.Remove().clone();
   tempCollection.Add(element.clone2());
   elementArray[amountOfElements++] = element;
  }
  collection = tempCollection;

 }

 public void Add(ElementInterface element){
     elementArray[amountOfElements++] = element;
 }

 public ElementInterface Remove(){
  ElementInterface element = elementArray[amountOfElements].clone2();
  elementArray[amountOfElements] = null;
  amountOfElements--;
  return element;
 }

 public boolean isEmpty(){
  return amountOfElements == 0;
 }

 public CollectionInterface clone()
 {
  return new Collection(this);
 }
}

Allright, it might seem a bit strange, and it is. But if I use the following code:

CollectionInterface collection = new Collection();
collection.Add(new Element("Foo"));
collection.Add(new Element("Bar"));
CollectionInterface collection2 = collection.clone();

The first one doesn’t contain any elements anymore. How is that possible?

Answer 1

You can not change the reference of an input parameter, as you try in the second constructor.

collection = tempCollection.

a) is this a syntax error,
b) collection is a local variable; assigning to it will change nothing on the outside of the constructor.