a recursive list paradigm jack beidler yaodong bi bob mccloskey computing sciences university of...

A Recursive List Paradigm

Jack Beidler

Yaodong Bi

Bob McCloskey

Computing Sciences

University of Scranton

Scranton, PA 18510

A Recursive List Paradigm

• List Paradigms

• A Recursive List Paradigm

• Examples

• Unfocused vs. focused paradigms

• From the recursive paradigm to a positional paradigm

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

A Recursive List Paradigm• McCarthy’s LISP

http://www-formal.stanford.edu/jmc/history/lisp/lisp.html

– 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

A Recursive List Paradigm

• ConstructorsRecursiveList ()

empty list

RecursiveList (Object Head)

non-empty list w empty tail

RecursiveList

(Object Head, RecursiveList Tail)list with tail

A Recursive List Paradigm

• Methodsboolean isEmpty()

RecursiveList tailOf()

Object getHead()

void setHead(Object NewHead)

void insert(RecursiveList List)

RecursiveList remove()

A Recursive List Paradigm

• Utility Methodsvoid swap(RecursiveList List)

String toString()

A Recursive List Paradigm

• What about iterator support– Recursion is the traversal method

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();

}

Examples• OrderedList Class (composed with RecursiveList)

…private void RecInsert (Object Obj, RecursiveList List){ if(List.isEmpty() || (c.compare(Obj, List.getHead())<0)) List.insert(new RecursiveList(Obj)); else RecInsert(Obj, List.tailOf());}

public void insert(Object Obj){ RecInsert(Obj, L);}

Examples• OrderedList Class (composed with RecursiveList)…private void Recmerge (RecursiveList Source1,

RecursiveList Source2, RecursiveList Merged){ if (Source1.isEmpty()) Merged.swap(Source2); else if (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()); }}

Examples• OrderedList Class (composed with RecursiveList) …

public void merge(OrderedList Source1,

OrderedList Source2){

Recmerge(Source1.L, Source2.L, this.L);

}

public String toString(){

return L.toString();

}

}

Examples

• OrderedList Class (composed with RecursiveList)– Simplicity of insert– Simplicity of merge– But what about iteration?? (be patient)

Examples

• What about iterator support

Unfocused vs. focused paradigms

• G&T– 1 Constructors

– 13 Methods

– 0 Utility Methods

• RecursiveList– 3 Constructors

– 6 Methods

– 2 Utility methods

Unfocused vs. focused paradigms

• S– 2 Constructors

– 14 Methods

– 0 Utility Methods

• RecursiveList– 3 Constructors

– 6 Methods

– 2 Utility methods

Unfocused vs. focused paradigms

• C&P– 1 Constructors

– 7 Methods

– 0 Utility Methods

• RecursiveList– 3 Constructors

– 6 Methods

– 2 Utility methods

From the recursive paradigm to a positional paradigm

• What about iteration?

• What about the positional paradigm?

• Constructed on top of the recursive paradigm.

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 offRear()

boolean backingUp()

From the recursive paradigm to a positional paradigm

RecursiveList Order = new RecursiveList(); … RecursiveListIterator It = new RecursiveListIterator(Order); for (It.front(); !It.offRear(); It.next()) System.out.print(((Integer)It.getObject())+"\t"); System.out.println(); for (It.rear(); It.backingUp(); It.prev()) System.out.print(((Integer)It.getObject())+"\t"); System.out.println();

Conclusions

• Lean, mean, well focused is usually better that the Swiss Army Knife approachhttp://www.cs.scranton.edu/~beidler/java/OneWay/

• It is even nicer with trees– RecBinTree Classhttp://www.cs.scranton.edu/~beidler/java/RecBinTree/