Array in Array and Output

As you are using following code :

        int arr[] = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
        int n = 6;
        n = arr[arr[n]];
        System.out.println(n);

By the above code

n=arr[arr[6]];

the value of arr[6]=7

n=arr[7];

As we can see the value of arr[7] = 8

int arr[] = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
        int n = 6;
        n = arr[arr[n]];
        System.out.println(n);

arr[n] with n == 6 -> the 7th element of your array, which is 7 (array indices are 0 based) arr[7] -> the 7th element of your array, being 8

First it will calculate the value of inner arr[n] which is arr[6], the value of this will be 7. Next it will substitute this value and your expression will evaluate to arr[7] which is 8.

Hence the final answer is 8.

The evaluation sequence is inner to outer.

    n = arr[arr[n]];

is equivalent to

    n = arr[n]; // start with index 6 and pick value 7
    n = arr[n]; // start with index 7 and pick value 8

Concentrate this line n = arr[arr[n]]; n=6 let int temp=arr[n]; so n=arr[temp]; as n=6 temp=arr[6]=7; temp=7; Now n=arr[temp]=arr[7]=8;

Array start with 0 so arr[0]=1,arr[1]=2 ... arr[6]=7

Final output arr[7]=8

Try this and see if it helps. The --> should be read as the same as.

int arr[] = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
for (int n = 0; arr[n] < arr.length; n++) {
       System.out.println("n = " +n + ", arr[" + n + "] = " + arr[n] + ", arr[arr[" + n +"]] --> arr[" + arr[n] + "] = " +arr[arr[n]]);
}

prints

n = 0, arr[0] = 1, arr[arr[0]] --> arr[1] = 2
n = 1, arr[1] = 2, arr[arr[1]] --> arr[2] = 3
n = 2, arr[2] = 3, arr[arr[2]] --> arr[3] = 4
n = 3, arr[3] = 4, arr[arr[3]] --> arr[4] = 5
n = 4, arr[4] = 5, arr[arr[4]] --> arr[5] = 6
n = 5, arr[5] = 6, arr[arr[5]] --> arr[6] = 7
n = 6, arr[6] = 7, arr[arr[6]] --> arr[7] = 8
n = 7, arr[7] = 8, arr[arr[7]] --> arr[8] = 9