1 / 37

Collections

Collections. Inheritance Polymorphism. Collection. 74 subclasses of Collection in Squeak 3.10 Some are abstract SequenceableCollection ArrayedCollection Most are concrete - Array, Bag, Dictionary, Interval, String, Set, Symbol. Collection as an Abstract Class.

chandler
Download Presentation

Collections

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Collections Inheritance Polymorphism

  2. Collection • 74 subclasses of Collection in Squeak 3.10 • Some are abstract • SequenceableCollection • ArrayedCollection • Most are concrete - Array, Bag, Dictionary, Interval, String, Set, Symbol Object-oriented Programming and Design - Johnson & Yoder - Day 3

  3. Collection as an Abstract Class • Collection has no instance variables. • Collection defines as subclassResponsibility • do: • add:, remove: (Changeable) • at:, at:put: (Sequenceable) Object-oriented Programming and Design - Johnson & Yoder - Day 3

  4. Collection as an Abstract Class • Template methods defined in terms of do: • select:, collect:, inject:into:, detect:ifAbsent:, size Object-oriented Programming and Design - Johnson & Yoder - Day 3

  5. Abstract class as type • All collections understand same protocol • do: iterate • select: subcollection • collect: transformed collection • inject:into: reduce collection to value • includes: does receiver contain it? • detect: find an element Object-oriented Programming and Design - Johnson & Yoder - Day 3

  6. Finding an element • numbers do: [:each | each isOdd ifTrue: [^firstOdd := each]]. • … firstOdd ... • numbers do: [:each | each isOdd ifTrue: [firstOdd ifNil ifTrue: [firstOdd := each]]] • firstOdd := numbers detect: [:each | each isOdd] Object-oriented Programming and Design - Johnson & Yoder - Day 3

  7. Find an Element • detect: aBlock ifNone: exceptionBlock • "Evaluate aBlock with each of the receiver's elements as the argument. Answer the first element for which aBlock evaluates to true." • self do: [:each | (aBlock value: each) • ifTrue: [^each]]. • ^exceptionBlock value Object-oriented Programming and Design - Johnson & Yoder - Day 3

  8. Transform a Collection • collect: aBlock • | newCollection | • newCollection := self species new. • self do: [:each | newCollection add: (aBlock value: each)]. • ^newCollection Object-oriented Programming and Design - Johnson & Yoder - Day 3

  9. Nonuniform Collection Protocol • add: and remove: are defined by collections whose size can change---Set, OrderedCollection, Bag, etc. • ArrayedCollection and Interval do not implement add: and remove: • at: and at:put: are defined by SequenceableCollection and Dictionary, but not by Set or Bag. Object-oriented Programming and Design - Johnson & Yoder - Day 3

  10. Collection Protocols • Collection do:, size, select:, collect:, inject:into:, includes:, detect: • ChangeableCollection add: addAll: remove: removeAll: • SequenceableCollection at: at:put first last , copyFrom:to: Object-oriented Programming and Design - Johnson & Yoder - Day 3

  11. Collection Menagerie • Array, String • Seq. • Symbol • Seq., read-only, unique • OrderedCollection • Seq., Changeable., a sequence • Set, Bag • Changeable Object-oriented Programming and Design - Johnson & Yoder - Day 3

  12. Collection Menagerie • Dictionary • at: and at:put: with any object as key • Interval • Seq., numeric, read-only • RunArray • Seq., compact encoding Object-oriented Programming and Design - Johnson & Yoder - Day 3

  13. OrderedCollection Instance variables: firstIndex, lastIndex A changeable sequenceable collection. Supports add:, remove:, at:, at:put: Object-oriented Programming and Design - Johnson & Yoder - Day 3

  14. OrderedCollection • at: anInteger • anInteger isInteger ifFalse: [ ^...]. • (anInteger < 1 or: [anInteger + firstIndex - 1 > lastIndex]) • ifTrue: [^...] • ^ super at: anInteger + firstIndex - 1 Object-oriented Programming and Design - Johnson & Yoder - Day 3

  15. OC::do: • do: aBlock • firstIndex to: lastIndex do: • [:index | aBlock value: (self basicAt: index)]. • size • ^ lastIndex - firstIndex + 1 Object-oriented Programming and Design - Johnson & Yoder - Day 3

  16. OC::add: • add: newObject • "Include newObject as one of the receiver's elements. Answer newObject." • ^ self addLast: newObject Object-oriented Programming and Design - Johnson & Yoder - Day 3

  17. OC::add: • addLast: newObject • "Add newObject to the end of the receiver. Answer newObject." • lastIndex = self basicSize ifTrue: [self makeRoomAtLast]. • lastIndex  lastIndex + 1. • self basicAt: lastIndex put: newObject. • ^ newObject Object-oriented Programming and Design - Johnson & Yoder - Day 3

  18. Using OrderedCollections • Suppose that list is an ordered collection. We want newList to be the reverse of list. • solution 1 • newList := OrderedCollection new. • list do: [:each | newList addFirst: each] Object-oriented Programming and Design - Johnson & Yoder - Day 3

  19. (continued) • solution 2 • newList := OrderedCollection newWithSize: list size. • index := list size. • list do: [:each | newList at: index put: each. • index := index - 1] Object-oriented Programming and Design - Johnson & Yoder - Day 3

  20. Interval • Instance variables: start, stop, step • 1 to: 1000 • 1 to: 1000 by: 3 • 1 to: 1000 do: [:each | sum  sum + each] Object-oriented Programming and Design - Johnson & Yoder - Day 3

  21. Interval • Number • to: stop • ^ Interval from: self to: stop by: 1 Object-oriented Programming and Design - Johnson & Yoder - Day 3

  22. Interval do: • do: aBlock • | n end | • n := 0. • end := self size - 1. • [n <= end] • whileTrue: • [aBlock value: start + (step * n). • n := n + 1] Object-oriented Programming and Design - Johnson & Yoder - Day 3

  23. Interval do: • do: aBlock • | aValue | • aValue := start. • step < 0 • ifTrue: [[stop <= aValue] • whileTrue: • [aBlock value: aValue. • aValue := aValue + step]] • ifFalse: [[stop >= aValue] • whileTrue: • [aBlock value: aValue. • aValue := aValue + step]] Object-oriented Programming and Design - Johnson & Yoder - Day 3

  24. Interval at: • at: anInteger • (anInteger >= 1 and: [anInteger <= self size]) • ifTrue: [^start + (step * (anInteger - 1))] • ifFalse: [^self subscriptBoundsError: anInteger] Object-oriented Programming and Design - Johnson & Yoder - Day 3

  25. Interval at:put: • at: anInteger put: anObject • "Provide an error notification that storing into an Interval is not allowed. " • self error: 'you can not store into an interval' Object-oriented Programming and Design - Johnson & Yoder - Day 3

  26. Set 3 19 $x 11 'hi!' A hash table. nil means an unused entry. Instance variables: tally Object-oriented Programming and Design - Johnson & Yoder - Day 3

  27. Hash • Sets and Dictionaries depend on the hash of their elements. • Each object has an integer hash value. • Some classes redefine hash. • Invariant: Equal (=) objects hash equally. Object-oriented Programming and Design - Johnson & Yoder - Day 3

  28. Classic Set Bugs • Some classes redefine hash. • Invariant: Equal (=) objects hash equally. • Bug 1: redefine = but not hash for some class. • aSet add: x. • x = y • ifTrue: [(aSet includes: y) • ifFalse: [self error]] Object-oriented Programming and Design - Johnson & Yoder - Day 3

  29. SequenceableCollection • = otherCollection • self == otherCollection ifTrue: [^ true]. • self species == otherCollection species • ifFalse: [^ false]. • ^ self hasEqualElements: otherCollection Object-oriented Programming and Design - Johnson & Yoder - Day 3

  30. SequenceableCollection • hash • | hash | • hash := self species hash. • 1 to: self size • do: [:i | hash := (hash + (self at: i) hash) hashMultiply]. • ^hash Object-oriented Programming and Design - Johnson & Yoder - Day 3

  31. Set bugs • Bug 2: Define = so it depends on state of the object. • Put object in set, then change its state, then try to find it! • Rule of thumb: only redefine = if object is immutable. Object-oriented Programming and Design - Johnson & Yoder - Day 3

  32. Set do: • do: aBlock • tally == 0 ifTrue: [^self]. • 1 to: array size do: • [:index | • | each | • (each := array at: index) ifNotNil: [aBlock value: each]] Object-oriented Programming and Design - Johnson & Yoder - Day 3

  33. Set includes: • includes: anObject • "Answer whether anObject is one of the receiver's elements." • ^(array at: (self findElementOrNil: anObject)) notNil Object-oriented Programming and Design - Johnson & Yoder - Day 3

  34. Set • findElementOrNil: anObject • "Answer the index of a first slot containing either a nil (indicating an empty slot) or an element that matches the given object. Answer the index of that slot or zero. Fail if neither a match nor an empty slot is found.” • | index | • index := self scanFor: anObject. • index > 0 ifTrue: [^index]. • self error: 'There is no free space in this set!'. Object-oriented Programming and Design - Johnson & Yoder - Day 3

  35. scanFor: anObject • | element start finish | • finish _ array size. • start _ (anObject hash \\ finish) + 1. • "Search from (hash mod size) to the end." • start to: finish do: • [:index | ((element _ array at: index) == nil or: [element = anObject]) • ifTrue: [^ index ]]. • "Search from 1 to where we started." • 1 to: start-1 do: • [:index | ((element _ array at: index) == nil or: [element = anObject]) • ifTrue: [^ index ]]. • ^ 0 "No match AND no empty slot" Object-oriented Programming and Design - Johnson & Yoder - Day 3

  36. Classic Collection Bugs • add: returns argument • (aSet add: 3) add: 2 --- wrong • aSet add: 3; add: 2 --- right • How are these different? • Array with: 3 with: 17 with: -9 • #(3 17 -9) Object-oriented Programming and Design - Johnson & Yoder - Day 3

  37. Conclusion • Collection is a typical class hierarchy • abstract classes on top • important interfaces, not completely regular • Missing ChangeableCollection • make assumptions (hash, =) about other classes Object-oriented Programming and Design - Johnson & Yoder - Day 3

More Related