Deleting nodes of Singly Linked List in Java

Question

I'm having a problem deleting nodes from singly linked lists in Java. I have a list, which has data of integers, and I need to delete all nodes, whose value can be divided by divided by four. I also need to move the head and tail pointers in case either of the head or tail elements are deleted. I wrote method for this, and most of the time it works just like I need it to, but sometimes it throws NullPointerException. How can I fix it? Here's my code:

public void delete(){
            Node temp = head, prev = null;
     
            if (temp != null && temp.data % 4 == 0) 
            {
                head = temp.next;
                temp = head;
            }

            while (temp.next != null) 
            {
               if (temp.data % 4 != 0) {
                   prev = temp;
                   temp = temp.next;
               }
               else {
               prev.next = temp.next;
                temp = prev.next;
               }
            }
            if (tail.data % 4 == 0) {
                tail = prev;
                tail.next = null;
                
            }
        }

Answer 1

while (temp.next != null) : temp may be null. And some more small problems.

This is due to too much complexity.

    public void delete() {
        Node prev = null;
        for (Node temp = head; temp != null; temp = temp.next) {
           if (temp.data % 4 == 0) {
               if (prev == null) {
                   head = temp.next;
               } else {
                   prev.next = temp.next;
               }
           } else {
               prev = temp;
           }
        }
        tail = prev;
    }

• The above sets prev to the valid previous node.
• The deletion considers deletion from head or from prev.next.
• The tail is updated to the last element.

Answer 2

in your while condition add one more null check:

while (null.= temp && null != temp.next)