How to clone ArrayList and also clone its contents?

Question

How can I clone an ArrayList and also clone its items in Java?

For example I have:

ArrayList dogs = getDogs();
ArrayList

        

Answer 1

You will need to clone the ArrayList by hand (by iterating over it and copying each element to a new ArrayList), because clone() will not do it for you. Reason for this is that the objects contained in the ArrayList may not implement Clonable themselves.

Edit: ... and that is exactly what Varkhan's code does.

Answer 2

The below worked for me..

in Dog.java

public Class Dog{

private String a,b;

public Dog(){} //no args constructor

public Dog(Dog d){ // copy constructor
   this.a=d.a;
   this.b=d.b;
}

}

 -------------------------

 private List<Dog> createCopy(List<Dog> dogs) {
 List<Dog> newDogsList= new ArrayList<>();
 if (CollectionUtils.isNotEmpty(dogs)) {
 dogs.stream().forEach(dog-> newDogsList.add((Dog) SerializationUtils.clone(dog)));
 }
 return newDogsList;
 }

Here the new list which got created from createCopy method is created through SerializationUtils.clone(). So any change made to new list will not affect original list

Answer 3

The other posters are correct: you need to iterate the list and copy into a new list.

However... If the objects in the list are immutable - you don't need to clone them. If your object has a complex object graph - they will need to be immutable as well.

The other benefit of immutability is that they are threadsafe as well.

Answer 4

Easy way by using commons-lang-2.3.jar that library of java to clone list

link download commons-lang-2.3.jar

How to use

oldList.........
List<YourObject> newList = new ArrayList<YourObject>();
foreach(YourObject obj : oldList){
   newList.add((YourObject)SerializationUtils.clone(obj));
}

I hope this one can helpful.

:D

Answer 5

A nasty way is to do it with reflection. Something like this worked for me.

public static <T extends Cloneable> List<T> deepCloneList(List<T> original) {
    if (original == null || original.size() < 1) {
        return new ArrayList<>();
    }

    try {
        int originalSize = original.size();
        Method cloneMethod = original.get(0).getClass().getDeclaredMethod("clone");
        List<T> clonedList = new ArrayList<>();

        // noinspection ForLoopReplaceableByForEach
        for (int i = 0; i < originalSize; i++) {
            // noinspection unchecked
            clonedList.add((T) cloneMethod.invoke(original.get(i)));
        }
        return clonedList;
    } catch (NoSuchMethodException | InvocationTargetException | IllegalAccessException e) {
        System.err.println("Couldn't clone list due to " + e.getMessage());
        return new ArrayList<>();
    }
}

Answer 6

Simple way is

ArrayList<Dog> dogs = getDogs();
ArrayList<Dog> clonedList = new ArrayList<Dog>(dogs);