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Chapter 18
The document discusses different sorting algorithms and methods. It introduces the concept of sortable objects that implement the Comparable interface and defines sorting algorithms like insertion sort, shell sort, selection sort, bubble sort, and quicksort. It also describes how sorting is implemented for arrays and collections in Java and the classes and methods involved in the sorting process.
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Chapter 18
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- 2. 18 Creating Sortable Objects Objectsare sortable when they implement the Comparable interface. Must implement compareTo() method Programmer must decide how to compare objects.
- 3. 18 Sorting Arrays TreeSet collectionsare sorted by default. Arrays class includes a sort() method. Items in array must be sortable (implement the Comparable interface).
- 4. 18 Sorting Algorithms Sortable interface Providesframework for sort classes Defines what it means to be sortable SortList class Holds the items in the list in an internal ArrayList Tracks: Number of items in the list Number of comparisons Number of exchanges Indicates whether algorithm steps should be displayed
- 5. 18 The Nested SortItemClass SortItem class: Implements Comparable interface Uses the compareTo() method to compare current object to an object passed in Uses the exchangeValues() method to exchange values when required
- 6. 18 Sorting Algorithms SortDriver class: Createsa sort object and submits a list to test the algorithm Will be modified several times as new sort algorithm classes are created SortAlgorithm class: Abstract base class (used to derive all sort algorithm classes) Provides common methods used by all the sort algorithms
- 7. 18 Insertion Sort Recursive insertion: Comparenew object to each object in the list until you find one of lesser value. Requires a lot of comparisons and exchanges.
- 8. 18 Shell Sort The shellsort is a variation on the insertion sort. Divides list into smaller sublists Sorts each sublist individually Then sorts sublists together Requires many comparisons, but fewer exchanges
- 9. 18 Selection Sort Selection sort: Scanslist to find lowest value then moves it to the left Repeat to find next lowest value Many comparisons with minimal exchanges
- 10. 18 Bubble Sort Bubble sort: Compareseach item to its neighbor and exchanges if necessary Largest items “bubble” to the top Poor performance due to many comparisons and many exchanges
- 11. 18 Quicksort Most widely usedsort method Partitions the list Use “pivot” to create right and left side Move item from left to right if larger than pivot Move item from right to left if smaller than pivot Each side is then partitioned and algorithm recurses until list is sorted
- 12. 18 Comparison of SortAlgorithms Direct comparison using random values