When overriding the clone () function, if the class has a reference field, then deep cloning is required.

@ Override
public Employee clone () throws CloneNotSupportedException {
  Employee e = (Employee) super.clone ();
  e.hireDay = (Date) hireDay.clone ();
  return e;
}

In case this is a link to a list:

class Class {
 List & lt; Class2 & gt; list;
 }

Overriding done:

Class e = (Class) super.clone ();
 for (int i = 0; i & lt; e.list.size (); i ++) {
 e.list.get (i) .clone ();
 }
 return e;

Is this correct?

Answer 1, authority 100%

The clone operation will create a new object with the same references to the same objects. If you want copies of objects in the list, you need to explicitly implement this. Those. write the following:

class B implements Cloneable {
  @Override
  protected Object clone () throws CloneNotSupportedException {
   return super.clone ();
  }
}
class A implements Cloneable {
  private List & lt; B & gt; list = new ArrayList & lt; & gt; ();
  @Override
  protected Object clone () throws CloneNotSupportedException {
    A clone = (A) super.clone ();
    clone.list = new ArrayList & lt; & gt; (list.size ());
    for (B b: list)
      clone.list.add ((B) b.clone ());
    return clone;
  }
}

Answer 2, authority 71%

List does not implement Cloneable , respectively, call clone through a variable / field of type List & lt; T & gt; will fail.

There are List implementations that override clone , such as ArrayList and LinkedList, but they do not deep copy the list. Those. they create a new list that contains the same elements.

From the documentation ArrayList.clone

Returns a shallow copy of this ArrayList instance. (The elements themselves are not copied.)

To deep copy a list, go through all the elements and clone each one.

For example, like this:

e.list = new ArrayList & lt; Class2 & gt; (list.size ());
for (Class2 item: list) e.list.add (item.clone ());

Similar question in English: How to clone ArrayList and also clone its contents?