Does java.lang.System.arraycopy() use a shallow copy?

Question

System.arraycopy() is a shallow copy method.

For an array of a primitive type, it will copy the values from one array to another:

int[] a = new int[]{1,2};
int[] b = new int[2];
System.arraycopy(a, 0, b, 0, 2);

b will be {1,2} now. Changes in a will not affect b.

For an array of a non-primitive type, it will copy the references of the object from one array to the other:

MyObject[] a = new MyObject[] { new MyObject(1), new MyObject(2)};
MyObject[] b = new MyObject[2];
System.arraycopy(a, 0, b, 0, 2);

b will contain a reference of new MyObject(1), new MyObject(2) now. But, if there are any changes to new MyObject(1) in a, it will affect b as well.

Are the above statements correct or not?

What are your thoughts on this so far? Have you tried writing some sample code? — Pops
– Pops, Commented May 23, 2011 at 19:06
So no sample code -1, not IDE -1? if you are a professor you will be out next semester. Sometimes I need a quick answer. Did you ask your co-worker some questions before you actually tried them before? If never, you are TOOOOOOOO smart. If you are a such smart guy, you need to be patient to other ordinary people. please ignore my any further questions later because most of time i may just ask without any sample and IDE things. — 5YrsLaterDBA
– 5YrsLaterDBA, Commented May 23, 2011 at 20:42

aioobe · Accepted Answer · 2011-05-23 19:18:05Z

0

Above statements are correct or not?

Yes, you are correct.

System.arraycopy always does a shallow copy, no matter if the array contains references or primitives such as ints or doubless.

Changes in array a will never affect array b (unless a == b of course).

But if any changes of new MyObject(1) in a, it will affect b as well.

Depends on what you mean. To be picky, a change to the new MyObject(1) will neither affect a nor b (since they only contain references to the object, and the reference doesn't change). The change will be visible from both a and b though, no matter which reference you use to change the object.

edited May 23, 2011 at 19:18

answered May 23, 2011 at 19:09

aioobe

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Platinum Azure · Accepted Answer · 2011-05-23 19:07:34Z

0

You're correct as long as you're specifically modifying properties and calling methods on your objects.

If you change where the reference points, for example with a[0] = new MyObject(1), then even though the objects were created with the same initialization data, they will now point to different instances of the object and a change to one instance will not be seen in the other reference (in array b).

answered May 23, 2011 at 19:07

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