Java Copy Constructor ArrayLists

Question

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);
    }

}

Answer 1

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.