Java Copy Constructor ArrayLists

constructor, copy, java

Solution

Note: Cloning the lists, isn't the same as cloning the elements in the list.

None of these approaches work the way you want them to:

//1
people = new ArrayList<Cool>(other.people);

//2
people = new ArrayList<Cool>();
for(Cool p : other.people) {
    people.add(p);
}

The approaches above will fill `people` such that it contains the same elements as `other.people`.

However, you don't want it to contain the same elements. You want to fill it with clones of the elements in `other.people`.

The best approach would be something like this:

people = new ArrayList<Cool>(other.people.size());
for(Cool p : other.people) {
    people.add((Cool)p.clone());
}

Make sure `Cool` implements `Cloneable`. Override `clone()` if necessary.

Problem

I am trying to create a copy constructor considering the object is mutable. My copy constructor is wrong; I can't seem to figure out what I am doing wrong. Please do NOT tell me to use `clone()`. How would I complete the copy constructor in this situation? I am new to Java and would really appreciate any help. ``` public class MyList { public ArrayList<Cool> people; /** * "people" variable as a new (empty) ArrayList of Cool objects. */ public MyPersonList() { people = new ArrayList<Cool>(0); } /** * A copy constructor which makes the right kind of copy considering * a Cool is mutable. */ public MyList(MyList other) { people = new ArrayList<Cool>(); for(Cool p:people) { people.add(p); } } ```

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