Leetcode top 100 question 2 Add two numbers

public class Solution {
    
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
    
        int[] num1=ListToArray(l1);
        int[] num2=ListToArray(l2);
        int i1=arrayToInt(num1);
        int i2=arrayToInt(num2);
        int result=i1+i2;
        int[] numResult=IntToArray(result);
        return headAdd(numResult);
    }


    public int[] ListToArray(ListNode l){
    
        ArrayList<Integer> num=new ArrayList<Integer>();
        int length=0;
        while(l!=null){
    
            num.add(l.val);
            l=l.next;
            length++;
        }
        int[] result=new int[length];
        for(int i=length-1,j=0;i>=0;i--,j++){
    
            result[i]=num.get(j);
        }
        return result;
    }

    // Returns a reverse order int,[1,2,3]=321
    public int arrayToInt(int[] num){
    
        int result=0;
        for(int i=num.length-1,l=num.length;i>=0;i--,l--){
    
            result+=num[i]*Math.pow(10,l-1);
        }
        return result;
    }

    public int[] IntToArray(int value){
    
        String str=String.valueOf(value);
        int[] intArray = new int[str.length()];
        for (int i = 0; i < str.length(); i++) {
    
            //  Traverse str Add each digit as intArray
            Character ch = str.charAt(i);
            intArray[i] = Integer.parseInt(ch.toString());
        }
        return intArray;
    }

    public ListNode headAdd(int[] num){
    
        ListNode head=new ListNode(num[num.length-1],null);
        ListNode l=head;
        for(int i=num.length-2;i>=0;i--){
    
            l.next=new ListNode(num[i],null);
            l=l.next;
        }
        return head;
    }
}

The train of thought is
1, Apply for an array of linked list lengths , Assign the value of the linked list to the array .
2, Convert these two arrays to int
3, Add two numbers
4, Convert the result to an array
5, Traversal through the array from tail to head , Use the tail interpolation method to build the linked list