How do I avoid .clone()?

Question

Consider this class

class MyClass {
  private MyData[] data;

  public MyData[] getData() {
    return data == null ? null : (MyData[]) data.clone();
  }

This is creating issue

Security - Method returns internal array

Exposing internal arrays directly allows the user to modify some code that could be critical. It is safer to return a copy of the array.

Considering clone is bad and should be avoided, what can I do to make this code better?

`System.arraycopy` or `Arrays.copyOf` both might do what you want. — , Oct 09 '15 at 20:25
what are you trying to achieve here? a read only array? otherwise just return data by itself. — WalterM, Oct 09 '15 at 20:25
@RalphWiggum that will return a shallow copy. Careful with that. — Luiggi Mendoza, Oct 09 '15 at 20:25
That doesn't look like an issue. Not all warnings are issues, they're just telling you that you should understand what you're doing and accept the consequences of what you're doing. But not an issue. — Luiggi Mendoza, Oct 09 '15 at 20:30
For anyone interested, [Why people are so afraid of using clone() (on collection and JDk classes)?](http://stackoverflow.com/questions/2597965/why-people-are-so-afraid-of-using-clone-on-collection-and-jdk-classes) — Richard Chambers, Oct 09 '15 at 20:33
see unmodifiable list http://stackoverflow.com/questions/16356232/unmodifiable-list-in-java — WalterM, Oct 09 '15 at 20:36

score 6 · Accepted Answer · answered Oct 09 '15 at 20:25

6

The easiest way to return a copy of the array would probably be by calling Arrays.copyOf:

public MyData[] getData() {
    return data == null ? null : Arrays.copyOf(data, data.length);
}

answered Oct 09 '15 at 20:25

Mureinik

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@sᴜʀᴇsʜᴀᴛᴛᴀ `Arrays#copyOf` uses `System.arraycopy` behind the scenes and this is easier to call/understand. – Luiggi Mendoza Oct 09 '15 at 20:40

Suresh Atta · Answer 2 · 2015-10-09T20:30:27.753

2

I too agree that clone is bad but Not on Arrays. Clone performs well on array. Your code is clean .Keep it as it is.

Soon I'll attach the reference for Josh Bloch words on array clone.

Josh Bloch on Cloning

Doug Lea goes even further. He told me that he doesn't use clone anymore except to copy arrays. You should use clone to copy arrays, because that's generally the fastest way to do it. But Doug's types simply don't implement Cloneable anymore. He's given up on it. And I think that's not unreasonable.

If you completely avoid cloning, the next best option is

System.arraycopy(array1,0, array2, 0, array1.length);

because

Arrays.copyOf creates another array object internally and returns it where as System.arraycopy uses the passed array.

edited Oct 09 '15 at 20:30

answered Oct 09 '15 at 20:25

Suresh Atta

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I would wipe any code that uses `.clone` and replace it with proper code. – Luiggi Mendoza Oct 09 '15 at 20:27
@daydreamer In that case `System.arraycopy` is your friend. – Suresh Atta Oct 09 '15 at 20:31

How do I avoid .clone()?

2 Answers2