I'm not sure if the following will result in deep or shallow copy?
public void viewImages(final String[] instancesFilename) { String[] instances = (String[])instancesFilename.clone(); } Is there a simple and fast way to deep copy a string array?
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3 Answers
Strings in Java are imutable(Can't change their value). So there is no detectable difference between a deep and shallow copy when copying strings.
And just to further reference: The copy will be shallow but that should not be a problem since strings are imutable.
Oh and funny fact: Strings can't be cloned with the clone method, so if you try to do a deep copy of strings with the clone method, you will get a CloneNotSupportedException.
6 Comments
Philipp Reichart
The author is asking to copy
String[], not String. The elements of instancesFilename could be changed later from the outside, so the OP wants to create a copy of the array.
Jon Skeet
Well it's detectable (are the references the same) but if you're using the strings properly, it shouldn't be significant.
Jon Skeet
@PhilippReichart: But the OP is already performing a clone - "deep copy" vs "shallow copy" in that context can only be about whether the strings are cloned or not - and as this answer states, it's almost always unimportant.
Miguel Ping
... But the String can be
intern()'d, which would make kind of a shallow copy :\
MTilsted
Your clone method will create a new independent array with new references to the same string objects. Which most likely is what you want/need. But your new references will point to the same String objects as the original Array. But I can't imagine why this would be a problem.
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The array class also has the copyOf method. This is generally what I use for creating copies of arrays. Heres and explanation of all of the differences: http://forum.codecall.net/topic/49450-copying-arrays/
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Here is an interesting article discussing using serialization to make deep copies.
The objects in the call graph do need to support serialization however in many business types of 3 Tier applications, that necessity is there.
The article provides a discussion of deep copy and shallow copy with some diagrams.
