clone() method (Shallow or Deep copying)

Question

In java books and online tutorials it is stated that Object.clone() method provides shallow copying unless Cloneable interface is used but in the code I implemented clone() method without using Cloneable interface and it is providing a deep copy instead of a shallow copy.

import java.util.GregorianCalendar;
public class test1 {

   public static void main(String[] args) {

      // create a gregorian calendar, which is an object
      GregorianCalendar cal = new GregorianCalendar();

      // clone object cal into object y
      GregorianCalendar y = (GregorianCalendar) cal.clone();

      // check if reference of y is equal to cal or not
      System.out.println(cal==y);//it's output should be true if this is a shallow copy but it is false.
   }
}

Duplicate of https://stackoverflow.com/questions/184710/what-is-the-difference-between-a-deep-copy-and-a-shallow-copy — Ashraff Ali Wahab, Aug 22 '18 at 14:01
A clone is a *different object,* so `==` will always evaluate to false. — VGR, Aug 22 '18 at 14:01
since clone method is said to generate shallow copy, then it should copy references i.e.,== should evaluate to true for two objects as their references would be same — Sc00by_d00, Aug 22 '18 at 14:04
`GregorianCalendar` does implement the `Cloneable` interface, so it should make a deep copy. — Ricardo Costeira, Aug 22 '18 at 14:05

Ricardo Costeira · Accepted Answer · 2018-08-22T14:14:44.563

0

GregorianCalendar does implement the Cloneable interface, so it should make a deep copy.

Edit: Java deals with references to objects only. So, in this case, since GregorianCalendar's clone method performs a deep copy, a way to copy the reference would be by assigning cal to y, i.e., y = cal.

edited Aug 22 '18 at 14:14

answered Aug 22 '18 at 14:07

Ricardo Costeira

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could you please explain how to use clone() method to create shallow copy – Sc00by_d00 Aug 22 '18 at 14:10
@Sc00by_d00 you create a shallow copy in your clone() implementation by simply returning `super.clone()`. You create a deep copy by calling `super.clone()` *and then* calling `clone()` on all fields. – DodgyCodeException Aug 22 '18 at 15:41

clone() method (Shallow or Deep copying)

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