[英]Generic Doubly Linked List Implementation
所以我有了通用双链表的基本通用植入。 我创建了一个insert方法,它将根据顺序添加一个节点。
public class DoublyLL <T extends Comparable<T>> {
DNode<T> head;
DNode<T> tail;
public void insertInOrder(T item) { //To create an "ordered" linked list
DNode <T> n = new DNode<>();
if (head == null) {
head = n;
n.data = item;
}
else {
DNode<T> temp = head;
while (temp != null && n.data.compareTo(temp.data) > 0) { // line 18
temp = temp.next;
}
if (temp == head) { //inserting node in first
head.prev = n;
n.next = head;
head = n;
n.data = item;
}
else if (temp == null) { // inserting at last
tail.next = n;
n.prev = tail;
tail = n;
n.data = item;
}
else { //inserting in middle
n.prev = temp.prev;
n.next = temp;
temp.prev.next = n;
temp.prev = n;
n.data = item;
}
}
}
@Override
public String toString() {
DNode temp = head;
String str = "";
while (temp != null) {
str += temp.data + " ";
temp = temp.next;
}
return str;
}
public static void main(String[] args) {
DoublyLL<Integer> list = new DoublyLL<>();
list.insertInOrder(2);
list.insertInOrder(222); //line 62
list.insertInOrder(22222);
System.out.println(list);
}
}
class DNode<T> {
T data;
DNode prev;
DNode next;
}
但是,当我运行此代码时,我在第18行和第62行得到了NullPointerException。我该怎么做才能使之成为有序列表,例如“ 2,22,2222”?
很难说没有堆栈跟踪的问题是什么,但是看起来像是
if (head == null) {
head = n;
n.data = item;
}
你应该有
if (head == null) {
head = n;
tail = n;
n.data = item;
}
否则,您的tail
保持为空。
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