Object cannot be converted to integer error

Question

I am writing a method to check if two int arrays are a rotation of each other. For example, [4,5,6,7,1,2] is a rotation of [1,2,4,5,6,7]

public static Boolean isRotation(int[] array1, int[] array2) {
        boolean result = false;
        if(array1.length != array2.length){
            result = false;
        }
        ArrayList<Integer> alist = new ArrayList<Integer>();
        LinkedList arr2 = new LinkedList(Arrays.asList(array2));

        if(arr2.contains(array1[0])){
            Iterator x = arr2.listIterator(arr2.indexOf(array1[0]));
            while(x.hasNext()){
             alist.add(x.next());
            }
            if(!(arr2.peek().equals(array1[0]))){
                alist.add(arr2.peek());
                arr2.pollFirst();
            }
        }//end of outer if loop. 
    //Compare the arraylist to array1;
        for(int i = 0; i<array1.length; i++){
            if(array1[i] != arr2.get(i)){
                result = false;
            }
        }//end of for loop checking
        return result; 
    }//end of method;

}//end of class;

However, I keep getting errors about object and integer. In Line alist.add(x.next()); and alist.add(arr2.peek());I cannot use the add method because I get the (argument mismatch; Object cannot be converted to Integer) error; and in this line if(array1[i] != arr2.get(i)){I get the incomparable types: int and Object error.

I don't see why the object in arr2, the linkedlist isn't an integer. Can anyone please explain what is wrong?

Answer 1

There are several issues with your code:

1. The use of raw types yields the aforementioned error.
2. the result variable is always false, which doesnt seem right. so double check your logic again.

That said, let's solve the raw type issue as follows with the use of generics:

ArrayList<Integer> alist = new ArrayList<>();
LinkedList<Integer> arr2 = new LinkedList<>(Arrays.asList(array2));

if(arr2.contains(array1[0])){
   Iterator<Integer> x = arr2.listIterator(arr2.indexOf(array1[0]));
   ...
   ...

At this point, there is still another issue,

the statement LinkedList<Integer> arr2 = new LinkedList<>(Arrays.asList(array2)); will not compile as array2 is of type int[] so the receiver type should be LinkedList<int[]> to make it compile but obviously that's not what you're after.

To solve the problem, you'll need to convert the int[]. you can do this as follows:

LinkedList<Integer> arr2 = Arrays.stream(array2)
                                 .boxed() 
                               .collect(Collectors.toCollection(LinkedList::new));

Answer 2

You are using generics in ArrayList :

ArrayList<Integer> alist = new ArrayList<Integer>();

Why not using it in :

LinkedList<Integer> arr2 = new LinkedList(Arrays.asList(array2));

and

Iterator<Integer> x = arr2.listIterator(arr2.indexOf(array1[0]));

Instead

LinkedList arr2 = new LinkedList(Arrays.asList(array2));

and

Iterator x = arr2.listIterator(arr2.indexOf(array1[0]));

---

Another solution(not useful in your case) without generics, you have to cast each Object :

alist.add((Integer) x.next());
          ^^^^^^^^^^^^^^^^^^

alist.add((Integer) arr2.peek());
          ^^^^^^^^^

if(array1[i] != (Integer) arr2.get(i)){
                ^^^^^^^^^

---

Another Solution

As @Aominè and the others mention you have several issues you have to fix them, I would just to solve your problem with another way :

public static Boolean isRotation(int[] array1, int[] array2) {
    List<Integer> list1 = Arrays.stream(array1).boxed().collect(Collectors.toList());
    List<Integer> list2 = Arrays.stream(array2).boxed().collect(Collectors.toList());
    
    int size = list1.size();

    for (int i = 0; i < size; i++) {
        if (list1.equals(list2)) {
            return true;
        }
        Collections.rotate(list2, -1);
    }
    return false;
}

Consider you have this two arrays (I consider that they are not empty and have the same length)

array1 = {4, 5, 6, 7, 1, 2}
array2 = {1, 2, 4, 5, 6, 7}

for each element in array1 move it to the end and check if it is equal with the second array of not :

First iteration :

array1 = {4, 5, 6, 7, 1, 2}
array2 = {1, 2, 4, 5, 6, 7}

not equal

Second iteration :

array1 = {4, 5, 6, 7, 1, 2}
array2 = {2, 4, 5, 6, 7, 1}//move 1 to the end

not equal

Second iteration :

array1 = {4, 5, 6, 7, 1, 2}
array2 = {4, 5, 6, 7, 1, 2}//move 2 to the end

Equal(and break)

If there are no match and the Iteration is end, then return false mean not Equals

Answer 3

Because you didn't specify the Integer type paramater:

LinkedList<Integer> arr2 = new LinkedList<>(Arrays.asList(array2));