CODEWITHSUNDEEP
javagenericsclonecopy-constructor
Haque1
Haque1

Reputation: 593

Generics, Copy Constructor, Clone method

I'm trying to create a generic container which has a copy-constructor. I'm having trouble using the clone method even though I have coded it in. Here's what I have so far:

public class MyBox<T> 
{
    private List<T> list;

    public MyBox()
    {
        list = new ArrayList<T>();
    }


    public void add(T item )
    {
        list.add(item);
    }

    public MyBox(MyBox<T> other) throws CloneNotSupportedException //this is giving me trouble
    {
        for(T item : other.list)
        {
            list.add((T) item.clone());
        }
    }
}

How can I get my copy-constructor to work?

Upvotes: 3

Views: 1638

Answers (4)

newacct
newacct

Reputation: 122439

Unfortunately in Java, there is no generic way to clone an object. Some classes have a public clone() method, which allows you to clone, but there is no common superclass or interface with a public clone() method. (In fact, because there is no common interface; classes don't even have to call it clone(); they could name it copy() or something else.) You could use reflection to see if there is a public clone() method, but that might be overkill.

Upvotes: 0

The Tran
The Tran

Reputation: 470

Usually you don't need to clone the item. 

public MyBox(MyBox<T> other)
{
    list = new ArrayList<T>(other.list);
}

When you add an item from collection A to collection B, the item is now referenced by both two collection A and B.

Upvotes: 3

Alex Stybaev
Alex Stybaev

Reputation: 4693

public MyBox(MyBox<T> other) 
{
      this.list = new ArrayList<T>(other.getList()); 
}

but you must add a getter for your list first in this case.

UPD. this makes shallow copy.

Upvotes: 0

user798182
user798182

Reputation:

How about restricting the generic to Clonable, then it's certain that the cloning of the items will be allowed:

public class MyBox<T extends Clonable> {
   ...

Upvotes: 0

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