Building a singly linked list

ListNode.java

/**
 * @description Unidirectional linked data structure
 * @author smallyu
 * @date 2019/10/23 13:22
 */
public class ListNode {
    int val;
    ListNode next;
    ListNode(int x) {
        val = x;
    }

    /**
     * @description Init ListNode with integer array
     * @param arr new int[]{1, 2, 3}
     */
    public ListNode(int[] arr) {
        // It will get some trouble if input empty array []
        // Because int field would init value to 0
        if (arr == null || arr.length < 1) {
            return;
        }
        this.val = arr[0];
        ListNode node = this;
        for (int i = 0; i < arr.length - 1; i++) {
            node.next = new ListNode(arr[i + 1]);
            node = node.next;
        }
    }

    /**
     * @description Print ListNode like array
     * @return String ArrayList.toString()
     */
    @Override
    public String toString() {
        List<Integer> list = new ArrayList<Integer> ();
        ListNode node = this;
        while (node != null) {
            list.add(node.val);
            node = node.next;
        }
        return list.toString();
    }
}


// ListNode listNode = new ListNode(new int[]{1, 2, 3});
// System.out.println(listNode);

// [1, 2, 3]