Delete First

Here is a the deleteFirst() method that may be added to LinkedList:

  public void deleteFirst()
  {
    if ( headPtr != null ) 
    {    
      headPtr = headPtr.getNext();  // headPtr now points at second node, or
                                    // is null if there was no second node.
    }
  }

Does the method work? It looks easy enough, but check that it works for all situations. Sometimes programmers overlook a situation.

Case I. List is already empty.

In this case, headPtr is null. The condition of the if statement detects this and the method does nothing.

Case II. One-node list.

headPtr currently points to that single node. That node's next member is null. So headPtr = headPtr.getNext() copies a null into headPtr, making the list empty.

Case III. Many-node list.

headPtr points to the first node. That node's next member is points to the second node. So headPtr = headPtr.getNext() copies a pointer to the second node into headPtr, removing the previous first node from the list.