A Recursive List Paradigm

1. A Recursive List Paradigm Jack Beidler Yaodong Bi Bob McCloskey Computing Sciences University of Scranton Scranton, PA 18510

2. A Recursive List Paradigm • List Paradigms • A Recursive List Paradigm • Examples • Unfocused vs. focused paradigms • From the recursive paradigm to a positional paradigm www.cs.scranton.edu/~beidler/java/

3. List Paradigms • Lists and the Java API • Interface List and its implementations • 25 methods • Swiss Army Knif Approach (multiple paradigms) • Focused Paradigms - a few well chosen coordinated methods • Array Analogy Paradigm • Positional Paradigm (One-way) • Positional Paradigm (Two-way) • Recursive Paradigm www.cs.scranton.edu/~beidler/java/

4. A Recursive List Paradigm • McCarthy’s LISP http://www-formal.stanford.edu/jmc/history/lisp/lisp.html • A no compromise recursive paradigm • A list: • isEmpty • or (head, tail) • head is an object • tail is a (possibly empty) sublist • A Java Implementation • 3 constructors • 6 methods • 2 utility methods www.cs.scranton.edu/~beidler/java/

5. A Recursive List Paradigm • Constructors RecursiveList ()empty list RecursiveList (Object Head) non-empty list w empty tail RecursiveList (Object Head, RecursiveList Tail)list with tail www.cs.scranton.edu/~beidler/java/

6. A Recursive List Paradigm • Methods boolean isEmpty() RecursiveList tailOf() Object getHead() void setHead(Object NewHead) void insert(RecursiveList List) RecursiveList remove() www.cs.scranton.edu/~beidler/java/

7. A Recursive List Paradigm • Utility Methods void swap(RecursiveList List) String toString() www.cs.scranton.edu/~beidler/java/

8. A Recursive List Paradigm • What about iterator support • Recursion is the traversal method www.cs.scranton.edu/~beidler/java/

9. Examples • OrderedList Class (composed with RecursiveList) import java.util.*; class OrderedList { private Comparator c; protected RecursiveList L; OrderedList (Comparator c){ this.c = c; L = new RecursiveList(); } www.cs.scranton.edu/~beidler/java/

10. Examples • OrderedList Class (composed with RecursiveList) … privatevoid RecInsert (Object Obj, RecursiveList List){ if(List.isEmpty() || (c.compare(Obj, List.getHead())<0)) List.insert(new RecursiveList(Obj)); else RecInsert(Obj, List.tailOf()); } publicvoid insert(Object Obj){ RecInsert(Obj, L); } www.cs.scranton.edu/~beidler/java/

11. Examples • OrderedList Class (composed with RecursiveList) … privatevoid Recmerge (RecursiveList Source1, RecursiveList Source2, RecursiveList Merged){ if (Source1.isEmpty()) Merged.swap(Source2); elseif (Source2.isEmpty()) Merged.swap(Source1); else { if (c.compare(Source1.getHead() , Source2.getHead())<0) Merged.insert(Source1.remove()); else Merged.insert(Source2.remove()); Recmerge(Source1, Source2, Merged.tailOf()); } } www.cs.scranton.edu/~beidler/java/

12. Examples • OrderedList Class (composed with RecursiveList) … publicvoid merge(OrderedList Source1, OrderedList Source2){ Recmerge(Source1.L, Source2.L, this.L); } public String toString(){ return L.toString(); } } www.cs.scranton.edu/~beidler/java/

13. Examples • OrderedList Class (composed with RecursiveList) • Simplicity of insert • Simplicity of merge • What about iterator support • One moment please www.cs.scranton.edu/~beidler/java/

14. G&T 1 Constructors 13 Methods 0 Utility Methods RecursiveList 3 Constructors 6 Methods 2 Utility methods Unfocused vs. focused paradigms www.cs.scranton.edu/~beidler/java/

15. S 2 Constructors 14 Methods 0 Utility Methods RecursiveList 3 Constructors 6 Methods 2 Utility methods Unfocused vs. focused paradigms www.cs.scranton.edu/~beidler/java/

16. C&P 1 Constructors 7 Methods 0 Utility Methods RecursiveList 3 Constructors 6 Methods 2 Utility methods Unfocused vs. focused paradigms www.cs.scranton.edu/~beidler/java/

17. From the recursive paradigm to a positional paradigm • What about iteration? • What about the positional paradigm? • Constructed as an extension of the recursive paradigm. www.cs.scranton.edu/~beidler/java/

18. From the recursive paradigm to a positional paradigm void front() void rear() void next() void prev() void append(Object O) void setObject(Object O) Object getObject() boolean currDefined() www.cs.scranton.edu/~beidler/java/

19. From the recursive paradigm to a positional paradigm RecursiveList Order = new RecursiveList(); … RecursiveListIterator It = new RecursiveListIterator(Order); for (It.front(); It.currDefined(); It.next()) System.out.print(((Integer)It.getObject())+"\t"); System.out.println(); for (It.rear(); It.currDefined(); It.prev()) System.out.print(((Integer)It.getObject())+"\t"); System.out.println(); www.cs.scranton.edu/~beidler/java/

20. Conclusions • Lean, mean, well focused is usually better that the Swiss Army Knife approach http://www.cs.scranton.edu/~beidler/java/OneWay/ • It is even nicer with trees • RecBinTree Class http://www.cs.scranton.edu/~beidler/java/RecBinTree/ www.cs.scranton.edu/~beidler/java/