现在尝试按索引删除节点。我想打印出带有索引的节点列表，以便用户可以选择所见的索引。我认为我的逻辑可以打印带有索引的列表，但没有输入:(
在玩弄这个的时候，我仍然无法打印节点列表，但是输出了“输入您希望删除的索引”并且能够接受用户的选择，但最终得到了 NullPointerException。
else if (menu.equals("d")) {
EntryNode temp = head;
while (temp != null) {
for (int i = 0; i < addressBook.length(); i++) {
//gets node at index
System.out.println(temp.getFirstName() + i);
temp = temp.getNext();
}
System.out.println(" ");
System.out.println("Please enter the index of the entry you wish to delete ");
int index = keyboard.nextInt();
addressBook.removeEntry(index);
}
}
删除方法：public void removeEntry(int index){
//delete from the head
if (index == 0) {
EntryNode temp = head;
head = temp.getNext();
temp.setNext(null);
head.setPrev(null);
size--;
}
//delete from the tail
else if (index == length()) {
EntryNode temp = tail;
temp.setPrev(null);
tail.setNext(null);
tail = temp.getPrev();
size--;
}
//in the middle
else {
EntryNode temp = head;
for (int i = 0; i < index; i++) {
//gets node at index
temp = temp.getNext();
}
//set node after temp's previous to temp's previous
temp.getNext().setPrev(temp.getPrev());
temp.getPrev().setNext(temp.getNext());
temp.setNext(null);
temp.setPrev(null);
size--;
}
}
NullPointerException 来自：
//set node after temp's previous to temp's previous
temp.getNext().setPrev(temp.getPrev());