How do I copy the contents of one ArrayList into another?

Answer 1

Suppose you have two arraylist of String type . Like

ArrayList<String> firstArrayList ;//This array list is not having any data.

ArrayList<String> secondArrayList = new ArrayList<>();//Having some data.

Now we have to copy the data of second array to first arraylist like this,

firstArrayList = new ArrayList<>(secondArrayList );

Done!!

Answer 2

You can use such trick:

myObject = new ArrayList<Object>(myTempObject);

or use

myObject = (ArrayList<Object>)myTempObject.clone();

You can get some information about clone() method here

But you should remember, that all these ways will give you a copy of your List, not all of its elements. So if you change one of the elements in your copied List, it will also be changed in your original List.

Answer 3

Supopose you want to copy oldList into a new ArrayList object called newList

ArrayList<Object> newList = new ArrayList<>() ;

for (int i = 0 ; i<oldList.size();i++){
    newList.add(oldList.get(i)) ;
}

These two lists are indepedant, changes to one are not reflected to the other one.

Answer 4

You need to clone() the individual object. Constructor and other methods perform shallow copy. You may try Collections.copy method.

Answer 5

to copy one list into the other list, u can use the method called Collection.copy(myObject myTempObject).now after executing these line of code u can see all the list values in the myObject.

Answer 6

Straightforward way to make deep copy of original list is to add all element from one list to another list.

ArrayList<Object> originalList = new ArrayList<Object>();
ArrayList<Object> duplicateList = new ArrayList<Object>();

for(Object o : originalList) {
    duplicateList.add(o);
}

Now If you make any changes to originalList it will not impact duplicateList.