A Bag Implementation That Links Data - Data Structures and Abstractions with Java - page 74

Question 9 Instead of calling the method getReferenceTo , could the method remove have
called the original definition of contains , as given in Segment 3.17? Explain.

Question 10 Revise the definition of the method contains so that it calls the private
method getReferenceTo .

Question 11 Revise the definition of the method getReferenceTo so that it controls its
loop by using a counter and numberOfEntries instead of currentNode .

Question 12 What is an advantage of the definition of getReferenceTo , as given in the
previous segment, over the one that the previous question describes?

3.24

The method clear . In the class ArrayBag , as given in the previous chapter, the method clear
called the methods remove and isEmpty to remove all entries from the bag. Since this definition
does not depend on how we represent the bag, we can use the same definition here in LinkedBag .
Thus, clear 's definition is

public void clear()
{

while (!isEmpty())
remove();
} // end clear

Note: Deallocating memory
After the method remove removes a node from a chain, you have no way to reference the
removed node, so you cannot use it. As Segment B.20 in Appendix B noted, the Java run-
time environment automatically deallocates and recycles the memory associated with such
nodes. No explicit instruction from the programmer is necessary or, in fact, possible to cause
deallocation to occur.

A Class Node That Has Set and Get Methods

Because Node is an inner class of the class LinkedBag , LinkedBag can access Node 's private data
fields directly by name. Doing so makes the implementation somewhat easier to write, read, and
understand, particularly for novice Java programmers. However, some computer scientists feel that
you should access a class's data fields only by calling accessor and mutator (set and get) methods.
This section adds these methods to Node and explores three ways define this class.

3.25

As an inner class. Suppose that we add the methods getData , setData , getNextNode , and
setNextNode to the inner class Node , as it appears in Listing 3-1. The class would then appear as
given in Listing 3-4.

LISTING 3-4

The inner class Node with set and get methods

private class Node
{

private T data; // entry in bag
private Node next; // link to next node

private Node(T dataPortion)
{