雙鏈表

Question

我正在試圖分裂我的雙向鏈表。但是我在sublist.head = mid.next上得到了空指針異常。這是否意味着sublist.head指向null？我該如何解決這個問題？

public void splitMid(DoublyLinkedList<T> sublist) 
{ 
    Node<T> current; 
    Node<T> mid; 
    int i; 
    if (head == null) 
    { 
     sublist.head = null; 
     sublist.rear = null; 
     sublist.count = 0; 
    } 
    else 
     if (head.next == null) 
     { 
      sublist.head = null; 
      sublist.rear = null; 
      sublist.count = 0; 
     } 
     else 
     { 
      mid = head; 
      current = head.next; 
      i = 1; 
      if (current != null) 
       current = current.next; 
      while (current != null) 
      { 
       mid = mid.next; 
       current = current.next; 
       i++; 
       if (current != null) 
        current = current.next; 
      } 
      sublist.head = mid.next; 
      sublist.rear = rear; 
      rear = mid; 
      rear.next = null; 
      sublist.count = count - i; 
      count = i; 
     } 

} 

Answer 1

如果本聲明：

sublist.head = mid.next; 

（攝於隔離）被拋出NPE，這意味着：

• sublist是null，或
• mid是null， OR
• both o f他們是null。

（你可以找出它與任何一個調試器&條件斷點，或通過添加一些臨時性跟蹤打印或斷言。）