Copy constructor of ArrayList<ArrayList<String>> not Working Java

Connor Rasmussen 0
Viewed 43

I am trying to create a copy to an Array List of Array Lists, but when doing so the addresses of all the individual elements are staying the same.

copySorted = new ArrayList<ArrayList<String>>(origSorted);

I would expect to generate a copy of origSorted without references to the original, but instead whenever I make a change to copySorted, it ends up happening to origSorted as well. I also tried the .clone() function with the same results.

arraylist java
2 Answers

It's not the changes to copySorted you're seeing, it's changes to the inner lists which are shared between the outer lists. If you want them to be completely distinct, you'll need to copy each one individually:

copySorted = new ArrayList<>(origSorted.size());
for (List<String> inner : origSorted) {
    copySorted.add(new ArrayList<>(inner));
}
shmosel0

Firstly you creat your ArrayList then creat your new arrayList by using the keyWord "new" so the new arraylist will be a new object seprate from the first arraylist like this:

ArrayList<String> myFirstArrayList = new ArrayList<>();//creat my first arrayList
    //add some objects
    myFirstArrayList.add("1");
    myFirstArrayList.add("2");
    myFirstArrayList.add("3");
    //print it
    System.out.println(myFirstArrayList);//[1, 2, 3]
    //creating a new arrayList by coping the first but we create a new arrayList by using the keyword "New"
    ArrayList<String> newArrayList= new ArrayList<>(myFirstArrayList);
    //print new arraylist
    System.out.println(newArrayList);//[1, 2, 3]
    //make some change in the new arraylist
    newArrayList.remove(1);
    //print the

    System.out.println(newArrayList);//[1, 3]
    System.out.println(myFirstArrayList);//[1, 2, 3]
    //my original arraylist still not changed b'z the two objects of arraylists are seperate.
SaidBoudad0
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