How to be cautious to prevent PRIVACY LEAKS when my class has array as instance variable?

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www - 19 Apr 2007 19:21 GMT

Hi,

My class is like following:

public MyClass
{
    private double[] _dataArray = new double[100];

    public void setDataArray(double[] inputArray) //not good!
    {
        _dataArray = inputArray;
    }

    public double[] getDataArray()
    {
        return _dataArray; //privacy leak
    }

}

An Eclipse plugin pointed out that both places could be causing privacy
leak. I know, in Java, array is a tricky data type. It is sort of like
Class variable. So passing array reference is like passing an object
reference: still one object, but with multiple references to it. Each
reference has the ability to modify the object.

What should I do to avoid such a potential problem?

Thank you very much.

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Tom Hawtin - 19 Apr 2007 19:37 GMT

> public MyClass
> {
[quoted text clipped - 3 lines]
> {
> _dataArray = inputArray;

_dataArray = inputArray.clone();

> }
>
> public double[] getDataArray()
> {
> return _dataArray; //privacy leak

return _dataArray.clone();

> }
>
> }
>
> An Eclipse plugin pointed out that both places could be causing privacy
> leak. [...]

If it was a List<Double> instead of double[], then use new
ArrayList<Double>(data). Collections.unmodifiableList is also a
possibility for outputs, but the unodifiable list tracks the original list.

Tom Hawtin

Reply to this Message

www - 19 Apr 2007 19:51 GMT

>> public MyClass
>> {
[quoted text clipped - 13 lines]
>>
>> }

I just checked my Java text book. Here is the answer:

public double[] getDataArray()
{
    double temp = new double[_dataArray.length];
    for(int i=0; i<_dataArray.length; i++)
    {
        temp[i] = _dataArray[i];
    }

    return temp;
}

I am wondering which way is better, comparing to your way (return
_dataArray.clone() ). Is your way a new feature in Java?

Reply to this Message

Tom Hawtin - 19 Apr 2007 20:46 GMT

> I just checked my Java text book. Here is the answer:
> [...]
> double temp = new double[_dataArray.length];

^[]

> I am wondering which way is better, comparing to your way (return
> _dataArray.clone() ). Is your way a new feature in Java?

No, it's been in there since 1.0. However for 1.4 and earlier you had to
write:

return (double[])_dataArray.clone();

To explicitly write a loop to copy array is nuts.

Tom Hawtin

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Eric Sosman - 19 Apr 2007 21:26 GMT

Tom Hawtin wrote On 04/19/07 15:46,:

>>I just checked my Java text book. Here is the answer:
>>[...]
[quoted text clipped - 11 lines]
>
> To explicitly write a loop to copy array is nuts.

Agreed: In tests discussed on this newsgroup at the
end of February and beginning of March, new-and-loop took
about 30% longer than clone(), and almost twice as long
as new-and-arrayCopy() ...

YMMV.

Signature

Eric.Sosman@sun.com

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How to be cautious to prevent PRIVACY LEAKS when my class has array as instance variable?

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