A List Implementation That Links Data - Data Structures and Abstractions with Java - page 344

{

private Node firstNode; // reference to first node
private int numberOfEntries;

public LList()
{

clear();
} // end default constructor

public final void clear() // note the final method
{

firstNode = null ;
numberOfEntries = 0;
} // end clear
< Implementations of the public methods add , remove , replace , getEntry , contains ,
getLength , isEmpty , and toArray go here. >
. . .

// Returns a reference to the node at a given position.
// Precondition: List is not empty;
// 1 <= givenPosition <= numberOfEntries.
private Node getNodeAt( int givenPosition)
{

< See Segment 14.7. >
} // end getNodeAt

private class Node // private inner class
{

< See Listing 3-4 in Chapter 3. >
} // end Node
} // end LList

As we discussed earlier, this version of the class will maintain only a head reference to the chain of
nodes. The data field firstNode is this head reference. Another data field, numberOfEntries , records
the number of entries in the current list. This number is also the number of nodes in the chain. The
default constructor simply 5initializes these data fields by calling clear . So initially, the list is empty,
firstNode is null , and numberOfEntries is 0.
As was noted in Appendix C, when a constructor cnalls another public method such as clear ,
that method should be final so that no subclass can override it, thereby changing the effect of the
constructor. Adding final to clear 's header is an implementation detail that is not reflected in
ListInterface . Recall from Appendix D that an interface cannot declare a method to be final.

VideoNote

The class LList

Adding to the End of the List
14.9

Let's choose the methods add and toArray as the core methods that we will implement first. We
have already defined the method clear , because the constructor calls it.