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Pitfalls of Linked Data Structures | page 7 of 9 |
A linked list must end with a null value. Without such a marker at the end of the list, a routine cannot "see" the end of the data structure. This assignment of a null value at the end of the list is often taken care of when a new node is packaged or through the use of a constructor.
When a reference variable is null , it is a programming error to invoke one of its methods or to try to access one of its instance variables. For example, a program may maintain a reference to the first node of a linked list, as follows:
ListNode first;
Initially, the list is empty and first is the null reference. At this point, it is a programming error to invoke one of the ListNode 's methods. The error would occur as a NullPointerException .
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