Java array: strange behaviour

Question

Everyone! I faced this strange behaviour of Java arrays. I cannot figure out why sampleArray is changing along with class' array? I find this unnatural.

public class Runner {
    public static void main(String[] args) {

            int sampleArray[] = new int[]{5, -1, 9 ,7 ,3 ,2 ,11 ,0 ,-7 ,6 , 10 ,9};
            SortArray testArray = new SortArray(sampleArray);
            System.out.println("Initial array is:");
            System.out.println(testArray.toString());

            testArray.sortArray();
            System.out.println("Sorted by Bubbles method array is:");
            System.out.println(testArray.toString());
            System.out.println("Initial array is");
            for (int i = 0; i<sampleArray.length; i++) {
                    System.out.print(sampleArray[i]+ " ");
            }

}

public class SortArray {
    private int anArray[];

    SortArray (int inputArray[]) {
         this.anArray = inputArray;
    }

    // Classic Bubbles sorting
    public void sortArray () {
            int arrayLength = this.anArray.length;
            for (int i = arrayLength; i > 0; i--) {
                    for (int j = 0; j < i-1; j++) {
                            if (anArray[j+1]<anArray[j]) {
                                    int tempVariable = anArray[j];
                                    anArray[j] = anArray[j+1];
                                    anArray[j+1] = tempVariable;
                            }
                    }
            }
    }

    @Override
    public String toString() {
            String arrayString = "";
            for (int i = 0; i<anArray.length; i++) {
                    arrayString = arrayString + anArray[i]+" ";
            }
            return arrayString;
    }

}

After all I keep getting:

Initial array is:
5 -1 9 7 3 2 11 0 -7 6 10 9 
Sorted by Bubbles method array is:
-7 -1 0 2 3 5 6 7 9 9 10 11 
Initial array is
-7 -1 0 2 3 5 6 7 9 9 10 11 
Process finished with exit code 0

So we see that initial array is changing as well. Why is this happening? It seems to be illogical as I never assign sampeArray another sequence and never change it directly in the code. But it's true. What to do in order to keep the initial array unaffected?

score 0 · Accepted Answer · answered Jun 10 '16 at 13:24

0

This is using a reference to the original array :

this.anArray = inputArray;

Any modification of anArray , is in fact a modification of the original array (both variables refer to the exact same Object).

Other than that, you may use Arrays.sort .

answered Jun 10 '16 at 13:24

Arnaud

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score -1 · Answer 2 · edited Jun 11 '16 at 08:25

-1

The only thing I have done to leave the initial array unaffected is to change the constructor:

SortArray (int inputArray[]) {
    this.anArray = inputArray.clone();
}

edited Jun 11 '16 at 08:25

dur

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answered Jun 11 '16 at 05:41

Andreas Gelever

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Please use the edit link on your question to add additional information. The Post Answer button should be used only for complete answers to the question. - [From Review](/review/low-quality-posts/12653706) – Jonas Czech Jun 11 '16 at 07:57
@JonasCz This **was** an answer. OP made a clone of the array to prevent the reference from being used. – OneCricketeer Jun 11 '16 at 08:37

Java array: strange behaviour

2 Answers2