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I have been doing questions in my programming book and came across this question:

What is the output of the following code?

int[][] array = new int[5][6];
int[] x = {1, 2};
array[0] = x;
System.out.println("array[0][1] is " + array[0][1]);

The book says the answer is:

array[0][1] is 2

I learned so far that resizing an array isn't possible. From what I understand of this problem is that

int[][] array = new int[5][6]

is creating 5 arrays of 6 elements which would display 0's by default if you displayed it on the console

000000
000000
000000
000000
000000

and now from what I understand is that 

array[0] = x;

is basically resizing the first array which has six elements of 0 into an array with 2 elements: 1 and 2.

What am I not understanding? Is it that 

array[0] = x;

is making it so it's actually just changing the index 0 element and index 1 element of the first array? and keeping index 2,3,4,5 elements as 0's in array[0]?

I found this question Resize an Array while keeping current elements in Java? but I don't think it helps me answer this question.

Community
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jakatak
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2 Answers2

12

This line

array[0] = x;

is not resizing the array array[0]; it's replacing the array array[0] such that array is now

12
000000
000000
000000
000000

The old array[0] is now discarded and it will be garbage collected. Now array[0] and x refer to the same array object, {1, 2}.

rgettman
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1
array[0]=x

This line is not resizing the array.Its making array[0] and x refer to same object. To make your concept more clear i would include a snippet

        int[][] array = new int[5][6];
        System.out.println("Initial length");

        for(int i=0;i<array.length;i++)
            System.out.println("length of array["+i+"] is " +array[i].length);

        int[] x = {1, 2};
        array[0] = x;//This line makes array[0] and x to refer to the same object

        System.out.println("After changes made");

        for(int i=0;i<array.length;i++)
            System.out.println("length of array["+i+"] is " +array[i].length);

        System.out.println("array[0][1]= "+array[0][1]);
        //changing the content of object referred by x

        x[0]=3;
        x[1]=6;

        System.out.println("After changing X");
        System.out.println("array[0][0]= "+array[0][0]+" array[0][1]="+array[0][1]);

Output

Initial length
length of array[0] is 6
length of array[1] is 6
length of array[2] is 6
length of array[3] is 6
length of array[4] is 6

After changes made

length of array[0] is 2
length of array[1] is 6
length of array[2] is 6
length of array[3] is 6
length of array[4] is 6

array[0][1]= 2

After changing content of object referred by x

array[0][0]= 3 array[0][1]=6

So you can observe that after array[0]=x if you change the content of object referred by x then changes are observed in both the arrays array[0] and x because they are referring to same object. Hope this helps you.Happy coding!!

aakansha
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