Data Structures and Algorithm Analysis - Computer Science at ...

138 Chap. 4 Lists, Stacks, and Queuesclass. Unfortunately, this obligation is hidden within the code of the dictionary (andpossibly in the user’s manual) rather than exposed in the dictionary’s interface. Asa result, some users of the dictionary might neglect to implement the overloading,with unexpected results. Again, the compiler will not catch this problem.The Java Comparable interface provides an approach to solving this problem.In a key-value pair implementation, the keys can be required to implementthe Comparable interface. In other applications, the records might be requiredto implement ComparableThe most general solution is to have users supply their own definition for comparingkeys. The concept of a class that does comparison (called a comparator)is quite important. By making these operations be generic parameters, the requirementto supply the comparator class becomes part of the interface. This designis an example of the Strategy design pattern, because the “strategies” for comparingand getting keys from records are provided by the client. Alternatively, theComparable class allows the user to define the comparator by implementing thecompareTo method. In some cases, it makes sense for the comparator class toextract the key from the record type, as an alternative to storing key-value pairs.We will use the Comparable interface in Section 5.5 to implement comparisonin heaps, and in Chapter 7 to implement comparison in sorting algorithms.4.5 Further ReadingFor more discussion on choice of functions used to define the List ADT, see thework of the Reusable Software Research Group from Ohio State. Their definitionfor the List ADT can be found in [SWH93]. More information about designingsuch classes can be found in [SW94].4.6 Exercises4.1 Assume a list has the following configuration:〈 | 2, 23, 15, 5, 9 〉.Write a series of Java statements using the List ADT of Figure 4.1 to deletethe element with value 15.4.2 Show the list configuration resulting from each series of list operations usingthe List ADT of Figure 4.1. Assume that lists L1 and L2 are empty at thebeginning of each series. Show where the current position is in the list.(a) L1.append(10);L1.append(20);L1.append(15);