Question

In JAVA, What is the difference between a shallow copy and a deep copy? Include a simple illustration of the difference.

Answer 1

1. Shallow Copy in Java;

==> When user use default implementation of clone method user get shallow copy of object means it create new instance(object) and copy all the field of object to that new instance and return it as object type we need to explicitly cast it back to our original object.

==> This is shallow copy of the object.

==> clone() method of the object class support shallow copy of the object.

==> The name shallow copy or shallow cloning in Java.

2. Deep Copy in Java

==> When user need own meaning of copy not to use default implementation user call it as deep copy, when user need deep copy of the object user need to implement according to our need.

==> For deep copy user need to ensure all the member class also implement the Cloneable interface and override the clone() method of the object class.

==> After that we override the clone() method in all those classes even in the classes where we have only primitive type members otherwise user would not be able to call the protected clone() method of Object class on the instances of those classes inside some other class

• In shallow copy, only fields of primitive data type are copied while objects references are not copied.
• Deep copy involves copy of primitive data type as well as objet references

shallow copy	deep copy
Shallow copy is fast and also less expensive.	Deep copy is slow and very expensive.
It is relatively fast	It is relatively slow.
Default version of clone method creates the shallow copy of an object.	To create the deep copy of an object, you have to override clone method.
Cloned Object and original object are not 100% disjoint.	Cloned Object and original object are 100% disjoint.
Cloned object and source object are not disjoint completely	Cloned objects and source objects are completely independent of each other.
Any changes made to cloned object will be reflected in original object or vice versa.	Any changes made to cloned object will not be reflected in original object or vice versa.