Passing only value for private members

Shaheen Ahamed S :

I am creating a class with one array as its private member and getter,setter method for that. I want set a value to that array using an array in main function. When I manipulate the array in main function, it should not affect the array present in that class.

I tried this code, but here the array is manipulated

class ClassB {

    private int[] a;

    ClassB() { }

    ClassB(int[] a) {
        this.a=a;
    }

    int[] geta() {
        return this.a;
    }

    void seta(int a[]) {
        this.a = a;
    }
}

public class ClassA{

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        System.out.println("Enter size : ");
        int n = sc.nextInt();
        int[] d = new int[n];
        System.out.println("Enter array elements : ");
        for (int i=0 ; i<n ; i++) {
            d[i] = sc.nextInt();
        }
        final ClassB cb2 = new ClassB(d);
        d[3] = 15;
        System.out.println("After changing array d : \n Values of array d :");
        for (int i=0 ; i<n ; i++) {
            System.out.println(d[i]);
        }
        System.out.println("Values of array a of cb2 :");
        int[] b = cb2.geta();
        for (int i=0 ; i<n ; i++) {
            System.out.println(b[i]);
        }
    }
}

I expect :

Enter size :

5

Enter array elements :
1
2
3
4
5
After changing array d :

 Values of array d :

1
2
3
15
5

Values of array a of cb2 :
1
2
3
4
5

But the actual output was :

Enter size :

5

Enter array elements :

1
2
3
4
5

After changing array d :

 Values of array d :

1
2
3
15
5

Values of array a of cb2 :

1
2
3
15
5

lealceldeiro :

You can make defensive copies in ClassB every time you set the array or need to return its values. Like this:

class ClassB {
    // ... code omitted for brevity

    ClassB(int[] a) {
        seta(a);
    }

    int[] geta() {
        int[] copy = new int[a.length];
        System.arraycopy(a, 0, copy, 0, a.length);
        return copy;
    }

    void seta(int a[]) {
        this.a = new int[a.length];
        System.arraycopy(a, 0, this.a, 0, a.length);
    }
}

Side notes:

If you really want to make ClassB immutable, you shouldn't have a setter for its values.
The utility System.arraycopy was used to create a copy of the arrays. Feel free to use here whatever fits better your needs (you may want to consider using a.clone()... this is a good topic about it: Why clone() is the best way for copying arrays?).

Additional readings:

Passing only value for private members

Guess you like