Java中的通用LinkedList克隆

Question

I want to clone any LinkedList, whether or not it holds things which can be primitive wrappers. I understand it can be a deep recursive call to get a true deep clone - but I want just one level of cloning. I cannot compile the following code :

   <T> LinkedList<T> deepCloneOneLevel (final LinkedList<T> input){
        if(input != null){
            LinkedList<T> clone = new LinkedList<>();
            for (T t: input){   
                clone.add(t.clone());  //error : clone() has protected access
            }
            return clone;
        }
        return null;
    }

Answer 1

As mentioned in the comments, Java's Cloneable is not a very friendly method to clone an object. So, You might need to define your Cloneable interface, and make sure

interface MyClone<T>{
  T clone();
}

And use that in your code

 <T extends MyClone<? super T>> LinkedList<T> deepCloneOneLevel (final LinkedList<T> input){
    if(input != null){
        LinkedList<T> clone = new LinkedList<>();
        for (T t: input){   
            clone.add(t.clone());
        }
        return clone;
    }
    return null;
}

And implementations of MyClone know if a shallow copy is enough or a deep copy is required

But what if the type doesn't implement MyClone ? Good question. We can add an overload that takes a clone "factory".

<T> LinkedList<T> deepCloneOneLevel (final LinkedList<T> input, Function<T,T> factory){
    if(input != null){
        LinkedList<T> clone = new LinkedList<>();
        for (T t: input){   
            clone.add(factory.apply(t));
        }
        return clone;
    }
    return null;
}

If your platform doesn't have Function yet, you can easily write your own, or use Guava's one.

Answer 2

Since clone() method is a big mess in java world, one solution may be to use apache commons SerializationUtils. It uses serialization to copy objects and as a result is slow. What is worse you'll have troubles if your class contains fields that do not support serialization. Here's an example:

<T extends Serializable> LinkedList<T> deepCloneOneLevel (final LinkedList<T> input) {
    if (input != null) {
        LinkedList<T> clone = new LinkedList<>();
        for (T t : input){
            clone.add(SerializationUtils.clone(t));
        }
        return clone;
    }
    return null;
}