Doubly Linked List - null pointer exception again
-
07-12-2019 - |
题
I'm getting this exception which seemed to be that I was doing things with a node that was null. Can someone explain how I am doing that? What is the constructor supposed to look like? I've seen it empty or with header and trailer dummy nodes..
//default constructor
public AddressList() {
}
//get size
public int size() {
return counter;
}
public void addEntryNode(){
//create the new node
EntryNode n = new EntryNode();
//set the data
System.out.println("Enter first name: ");
n.myFirstName = keyboard.next();
n.setFirstName(n.myFirstName);
System.out.println("Enter Last Name: ");
n.myLastName = keyboard.next();
n.setLastName(n.myLastName);
System.out.println("Enter Email Address: ");
n.myEmail = keyboard.next();
n.setEmail(n.myEmail);
System.out.println("Enter Phone Number: ");
n.myPhoneNum = keyboard.next();
n.setPhoneNum(n.myPhoneNum);
n.setIndex(index);
//add nodes to head of list
head.setPrev(n);
n.setNext(head);
head = n;
//up the count and index
counter++;
解决方案
Well, this seems like the most likely fix. Initialize the head to null, and add a condition for when the list is empty.
public AddressList() {
head = null
}
And your condition would look like this:
if (head == null) { // empty list
head = n
}
else {
head.setPrev(n);
n.setNext(head);
head = n;
}
不隶属于 StackOverflow