List Implementations That Use Arrays - Data Structures and Abstractions with Java - page 326

FIGURE 13-5

Removing Bob by shifting array entries

Alice Bob Carla Doug Haley

Alice Carla Carla Doug Haley

Alice Carla Doug Doug Haley

Haley Haley

Alice Carla Doug

Alice Carla Doug Haley

Note that no shift is necessary if the deletion is at the end of the list. In that case, the last entry
in the list is at position numberOfEntries , since the first entry is at position 1. If givenPosition
equals numberOfEntries , the for statement in removeGap will exit immediately. Even so, remove
will not call removeGap in this case. Notice that removeGap 's precondition requires givenPosition
to be less than numberOfEntries , and the remove method enforces this precondition. You can
enable the assert statement in removeGap to verify this enforcement.
This precondition of removeGap implies that the method should not be called if a list is empty.
In fact, remove ensures that requirement is followed.

Question 9 Figure 13-5 shows Haley shifted toward the beginning of the array. Actually, the
reference to Haley is copied, not moved, to its new location. Should we assign null to Haley's
original location?

Question 10 The method clear could simply set the data field numberOfEntries to zero.
Although the list methods would correctly behave as though the list was empty, the objects
that were in the list would remain allocated. Suggest at least two ways that clear could
deallocate these objects.

13.12

The methods replace and getEntry . Replacing a list entry and retrieving a list entry are two
straightforward operations when an array is used to represent the entries. You simply replace or
retrieve the object that is in the indicated array location. Like earlier methods, replace and
getEntry are responsible for validating the given position. Like remove , these methods do not
need an explicit test for an empty list to behave correctly. The assert statement is available to
verify this claim during testing.
The following methods implement these two operations:

public boolean replace( int givenPosition, T newEntry)
{

boolean isSuccessful = true ;
if ((givenPosition >= 1) && (givenPosition <= numberOfEntries))
{

assert !isEmpty();
list[givenPosition - 1] = newEntry;

}