Chapter 8, Design Patterns Factory

1. Chapter 8, Design Patterns Factory

2. A Pattern Taxonomy Pattern Creational Pattern Behavioral Pattern Structural Pattern Singleton Abstract Factory Builder Factory Prototype Composite Decorator Adapter Bridge Façade Proxy Iterator Command Observer Template Strategy

3. Animated Sorting Algorithms • These programs will display multiple sorting routines running in parallel !! • The primary design method will be a factory • There will be a factory that produces different sorting routines • Another factory will produce different sorting displays • The algorithms will be developed through several iterations to illustrate these components Run Those Sorts!

4. Initial Version • The first attempt uses the Template design pattern; the methods are • The subclasses define the following methods

5. Creating Random Data protected void scramble() { arr = new int[getSize().height / 2]; for (int i = arr.length; --i >= 0;) { arr[i] = i; } for (int i = arr.length; --i >= 0;) { int j = (int)(i * Math.random()); swap(arr, i, j); } } • This swap routine will be used by the sorting methods private void swap(int a[], int i, int j) { int T; T = a[i]; a[i] = a[j]; a[j] = T; }

6. The paintFrame Routine • The integer value will control the height of the line that is drawn protected void paintFrame(Graphics g) { Dimension d = getSize(); g.setColor(Color.white); g.fillRect(0, 0, d.width, d.height); g.setColor(Color.black); int y = d.height - 1; double f = d.width / (double) arr.length; for (int i = arr.length; --i >= 0; y -= 2) g.drawLine(0, y, (int)(arr[i] * f), y); }

7. One Sorting Routine protected void MYSTERY(int a[]) { for (int i = a.length; --i >= 0; ) for (int j = 0; j < i; j++) { if (a[j] > a[j+1]) swap(a, j, j + 1); pause(); } } • Solve the MYSTERY; what name really belongs here for this sort? • What is the complexity of this sort if there are n items • The code for this sort is short, so does that mean it will run quickly?

8. Here is Quicksort protected void quickSort(int a[], int lo0, int hi0) { int lo = lo0; int hi = hi0; int mid; pause(); if (hi0 > lo0) { mid = a[(lo0 + hi0) / 2 ]; while(lo <= hi) { while ((lo < hi0) && (a[lo] < mid)) ++lo; while ((hi > lo0) && (a[hi] > mid)) --hi; if(lo <= hi) { swap(a, lo, hi); pause(); ++lo; --hi; } } if(lo0 < hi) quickSort(a, lo0, hi); if(lo < hi0) quickSort(a, lo, hi0); } }

9. The algorithm Method and Initialization protected void algorithm() { if ("BubbleSort".equals(algName)) bubbleSort(arr); else if ("QuickSort".equals(algName)) quickSort(arr, 0, arr.length - 1); else bubbleSort(arr); } protected void initAnimator() { setDelay(20); algName = "BubbleSort"; String at = getParameter("alg"); if (at != null) algName = at; scramble(); }

10. Using the Strategy Design Pattern • The class relations This sort() method is abstract

11. The Sort Subclasses class BubbleSortAlgorithm extends SortAlgorithm { void sort(int a[]) { for (int i = a.length; --i>=0; ) for (int j = 0; j<i; j++) { if (a[j] > a[j+1]) swap(a, j, j+1); pause(); } } public BubbleSortAlgorithm(AlgorithmAnimator animator) { super(animator); } } • Carefully describe the changes that are needed for the Quicksort subclass

12. public class QuickSortAlgorithm extends SortAlgorithm { public QuickSortAlgorithm(AlgorithmAnimator animator) { super(animator); } protected void QSort(int a[], int lo0, int hi0) { // the partition process goes here if( lo0 < hi ) QSort( a, lo0, hi ); if( lo < hi0 ) QSort( a, lo, hi0 ); } } public void sort(int a[]) { QSort(a, 0, a.length - 1); } }

13. Creating the Concrete Algorithms Run Sort2

14. Using an Algorithm Factory

15. The Interface and Implementation public interface SortAlgorithmFactory { SortAlgorithm makeSortAlgorithm(String algName); } public class StaticAlgoFactory implements SortAlgorithmFactory { public SortAlgorithm makeSortAlgorithm(String algName) { if ("BubbleSort".equals(algName)) return new BubbleSortAlgorithm(animator); else if ("QuickSort".equals(algName)) return new QuickSortAlgorithm(animator); else return new BubbleSortAlgorithm(animator); } protected AlgorithmAnimator animator; public StaticAlgoFactory(AlgorithmAnimator animator) { this.animator = animator; } }

16. Sort2 Revised public class Sort2 extends AlgorithmAnimator { public void initAnimator() { setDelay(20); algName = "BubbleSort"; String at = getParameter("alg"); if (at != null) algName = at; algorithmFactory = new StaticAlgoFactory(this); theAlgorithm =algorithmFactory.makeSortAlgorithm(algName); scramble(); } protected void algorithm() { if (theAlgorithm != null) theAlgorithm.sort(arr); } protected void scramble() // same as before protected void paintFrame(Graphics g) // same as before protected int arr[]; protected String algName; protected SortAlgorithm theAlgorithm; protected SortAlgorithmFactory algorithmFactory; }

17. The Factory Design Pattern - 1

18. The Factory Design Pattern - 2