Is clone() in java shallow copy?

java deep-copy shallow-copy
Josh Morrison picture Josh Morrison · Mar 11, 2011 · Viewed 12.6k times · Source

Is clone() in java a shallow copy?

Eventually this gets to the clone() method of Object (the uppermost class), which creates a new instance of the same class as the object and copies all the fields to the new instance (a "shallow copy").

I read this from wikipedia.

I don't understand why it is a shallow copy. clone() will create a new instance with all fields. Is this just a deep copy? confused. Need some explanation for me.

Answer

Chris Jester-Young picture Chris Jester-Young · Mar 12, 2011

The default Object.clone() is indeed a shallow copy. However, it's designed to throw a CloneNotSupportedException unless your object implements Cloneable.

And when you implement Cloneable, you should override clone() to make it do a deep copy, by calling clone() on all fields that are themselves cloneable.

Related questions

clearing or set null to objects in java

I was recently looking into freeing up memory occupied by Java objects. While doing that I got confused about how objects are copied (shallow/deep) in Java and how to avoid accidently clearing/nullifying objects while they are still in …

Read More
What is the difference between being shallowly and deeply equal? How is this applied to caching?

Found the following in my notes, but I am unable to make sense of it: Primitive type wrapper classes implement caching for a limited number of values. This guarantees that a limited number of deeply equal wrapper objects are also …

Read More
How to clone ArrayList and also clone its contents?

How can I clone an ArrayList and also clone its items in Java? For example I have: ArrayList<Dog> dogs = getDogs(); ArrayList<Dog> clonedList = ....something to do with dogs.... And I would expect that objects in …

Read More