Doubly Linked List implementation in Java, missing "remove value" method

DoublyLinkedList.java

    //same ListNode as SLL except with prev, getPrevious, setPrevious
    
    public class ListNode {
        private int value;
        private ListNode prev;
        private ListNode next;
        
        //need constructor, get/set values/prev/next
        
        public ListNode() {
        }
        
        public ListNode(int value) {
            this.value = value;
        }
        
        public ListNode(int value, ListNode next) {
            this.value = value;
            this.next = next;
        }
        
        public ListNode(int value, ListNode next, ListNode prev) {
            this.value = value;
            this.next = next;
            this.prev = prev;
        }
        
        public int getValue() {
            return this.value;
        }
        
        public void setValue(int value) {
            this.value = value;
        }
        
        public ListNode getNext() {
            return this.next;
        }
        
        public void setNext(ListNode next) {
            this.next = next;
        }
        
        public ListNode getPrev() {
            return this.prev;
        }
        
        public void setPrev(ListNode prev) {
            this.prev = prev;
        }
    }
    
   
        //has root, tail, current size called number, max size called maximum
        //getSize, getMax, setRoot, insert at end, insert at n, remove nth, remove value
        
        private ListNode root;
        private ListNode tail;
        private int number;
        private int maximum = 15;
        
        public class List {
            public void setRoot(ListNode root) {
                this.root = root;
            }
            
            public int getSize() {
                return this.number;
            }
            
            public int getMax() {
                return this.maximum;
            }
            
            public void insert_at_end(int value) {
                ListNode tmp = new ListNode(value);
                ListNode tmp2 = this.tail;
                
                if (number == maximum) {
                    return "Sorry, this list is full.";
                }
                
                if (this.root == null) {
                    this.root = tmp;
                }
                
                tmp.setPrev(tmp2);
                tmp2.setNext(tmp);
                this.setTail(tmp);
                this.number++;
            }
            
            public void insert_at_nth(int value, int n) {
                ListNode tmp = new ListNode(value);
                ListNode tmp2 = this.root;
                
                if (number == maximum) {
                    return "Sorry, this list is full.";
                }
                
                if (n == 0) {
                    tmp2.setPrev(tmp);
                    tmp.setNext(tmp);
                    this.setRoot(tmp);
                }
                
                if (this.root == null) {
                    this.setRoot(tmp);
                }
                
                for (int i = 0; i < n; i++) {
                    while (tmp2.getNext() != null) {
                        tmp2 = tmp2.getNext();
                    }
                }
                
                tmp.setPrev(tmp2);
                tmp.setNext(tmp2.getNext());
                tmp2.setNext(tmp);
                tmp2.getNext().setPrev(tmp);
                number++;
            }
            
            public void remove_at_nth(unsigned int n) {
                ListNode tmp = this.root;
                
                if (this.root == null) {
                    return;
                }
                
                if (n == 0) {
                    tmp.getNext().setPrev() = null;
                    this.setRoot(tmp.getNext());
                } 
                
                for (int i = 0; i < n; i++) { //navigate to n
                    while (tmp.getNext() != null) {
                        tmp = tmp.getNext();
                    }
                }
                
                tmp.getPrev().setNext(tmp.getNext());
                tmp.getNext().setPrev(tmp.getPrev());
                number--;
                   
            }
            
        }