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

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

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A Recursive List Paradigm

• McCarthys LISP
• http//www-formal.stanford.edu/jmc/history/lisp/li
  sp.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

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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

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A Recursive List Paradigm

• Methods
• boolean isEmpty()
• RecursiveList tailOf()
• Object getHead()
• void setHead(Object NewHead)
• void insert(RecursiveList List)
• RecursiveList remove()

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A Recursive List Paradigm

• Utility Methods
• void swap(RecursiveList List)
• String toString()

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A Recursive List Paradigm

• What about iterator support
• Recursion is the traversal method

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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()

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Examples

• OrderedList Class (composed with RecursiveList)
• private void RecInsert
• (Object Obj,
• RecursiveList List)
• if(List.isEmpty()
• (c.compare(Obj, List.getHead())lt0))
• List.insert(new RecursiveList(Obj))
• else RecInsert(Obj, List.tailOf())
• public void insert(Object Obj)
• RecInsert(Obj, L)

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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())lt0)
• Merged.insert(Source1.remove())
• else Merged.insert(Source2.remove())
• Recmerge(Source1, Source2, Merged.tailOf())

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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()

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Examples

• OrderedList Class (composed with RecursiveList)
• Simplicity of insert
• Simplicity of merge
• What about iterator support
• One moment please

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Unfocused vs. focused paradigms

• GT
• 1 Constructors
• 13 Methods
• 0 Utility Methods

• RecursiveList
• 3 Constructors
• 6 Methods
• 2 Utility methods

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Unfocused vs. focused paradigms

• S
• 2 Constructors
• 14 Methods
• 0 Utility Methods

• RecursiveList
• 3 Constructors
• 6 Methods
• 2 Utility methods

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Unfocused vs. focused paradigms

• CP
• 1 Constructors
• 7 Methods
• 0 Utility Methods

• RecursiveList
• 3 Constructors
• 6 Methods
• 2 Utility methods

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From the recursive paradigm to a positional
paradigm

• What about iteration?
• What about the positional paradigm?
• Constructed as an extension of the recursive
  paradigm.

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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()
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From the recursive paradigm to a positional
paradigm

• RecursiveList Order new RecursiveList()
• RecursiveListIterator It new
• RecursiveListIterator(Or
  der)
• 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()

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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/RecBinTre
  e/