Java Reference
In-Depth Information
public T getEntry( int givenPosition)
{
T result = null ; // return value
if ((givenPosition >= 1) && (givenPosition <= list.size()))
{
assert !isEmpty();
result = list.get(givenPosition - 1);
} // end if
return result;
} // end getEntry
13.23
Remaining methods. The method clear uses the statement
list.clear();
to remove all entries from the vector and hence from the list. Likewise, the implementations of the
methods contains , getLength , and isEmpty are simple and left as exercises.
Note: The methods in our class VectorList function similarly to methods in Java's class
Vector , but their specifications differ. In implementing ListInterface , VectorList simply
invokes methods of the class Vector . VectorList is an example of an adapter class, which
we described in Segment C.3 of Appendix C.
Note: Since Java's class Vector uses an array in its implementation, the two implementa-
tions of the ADT list that we have covered so far are array based. Both implementations use a
resizable array to contain the list's entries, and so a list can grow in size as needed.
Note: Writing VectorList is certainly easier than writing the array-based implementa-
tion that this chapter describes. Since the methods of VectorList invoke the methods of
Vector , they can require more execution time than those of AList . However, this time
increase typically is insignificant.
Note: When you use an array or a vector to implement the ADT list,
Retrieving the entry at a given position is fast
Adding an entry at the end of a list is fast
Adding or removing an entry that is between other entries requires shifting them within
the array
Increasing the size of the array or vector requires copying entries
C HAPTER S UMMARY
The two implementations of the ADT list in this chapter use an array to store the items in a list.
Using an array results in a straightforward implementation of the list, but it is somewhat more involved than
the implementations of either the ADT bag or the ADT stack.
An array provides direct access to any of its elements, so a method such as getEntry has a simple,
efficient implementation.
 
 
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