	CS 535 Object-Oriented Programming & Design Fall Semester, 2001 More Collections
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Contents of Doc 10, More Collections


Doc 10, More Collections Slide # 2

Arrays

Similar to arrays in other languages

Once created can not grow

Some Array Operations

a := #( 1 3 5 7 6 4 2 ).
b := Array with: 2 with: 9.
   
secondElement := a at: 2.
firstElement := a first.
a 
   at: 1
   put: 12.
   
jointList := a , b.      "Comma concatinates collections"
sublist := a 
   copyFrom: 2
   to: 4.
copyList := a copyUpTo: 6.
copyWithout := jointList copyWithout:  2.
   
fiveIndex := a indexOf: 5.
location := a 
   indexOfSubCollection: #( 6 4) 
   startingAt: 2 
   ifAbsent: [-1].
a
   replaceAll: 3
   with: 12.
numberOfElements := a size.
even := jointList select:  [:each | each even].


Doc 10, More Collections Slide # 3

OrderedCollections

A growable array

When add elements, OrderedCollection object grows if needed

Like Java's Vector or ArrayList
Use more than arrays

Some OrderedCollection Operations

a := #( 1 3 5 7 6 4 2 ) asOrderedCollection.
b := OrderedCollection new.
b
   add: 2;
   add: 5.
   
secondElement := a at: 2.
firstElement := a first.
a 
   at: 1
   put: 12.
      
jointList := a , b.
sublist := a 
   copyFrom: 2
   to: 4.
copyList := a copyUpTo: 6.
copyWithout := jointList copyWithout:  2.
   
fiveIndex := a indexOf: 5.
location := a 
   indexOfSubCollection: #( 6 4) 
   startingAt: 2 
   ifAbsent: [-1].
a
   replaceAll: 3
   with: 12.
numberOfElements :=  a size.
evenElements := jointList select:  [:each | each even].
   
a remove: 5
Doc 10, More Collections Slide # 4

Dictionary

A hash table, like Java's Hashtable or HashMap

In arrays and ordered collections indexes are integers

In hash tables indexes can be any object

| phoneNumbers |
phoneNumbers := Dictionary new.
phoneNumbers
   at: 'whitney'
   put: '594-3535'.
phoneNumbers
   at: 'beck'
   put: '594-6807'.
phoneNumbers
   at: 'donald'
   put: '594-7248'.
   
phoneNumbers at: 'donald'       "Returns '594-7248' "
   
phoneNumbers
   at: 'sam'
   ifAbsent: ['Not found'].
   
phoneNumbers do: 
   [:value | 
   Transcript
      show: value;
      cr].


Doc 10, More Collections Slide # 5

"Continued from previous slide"

keyphoneNumbers keysDo: 
   [:key | 
   Transcript
      show: key;
      cr].
   
phoneNumbers keysAndValuesDo: 
   [:key :value | 
   Transcript
      show: key;
      tab;
      show: value;
      cr].


Doc 10, More Collections Slide # 6

Strings & Symbols

A String is an array of characters

'The cat in the hat'

Characters can be any Unicode character

Symbols are strings that are represented uniquely

Examples of symbols

#ASymbol
#'CanUseSingleQuotes'
#cat

There is only one copy of a symbol with a given sequence of characters in the image

'cat' = 'cat'      "true"
'cat' == 'cat'    "false"
   
#cat = #cat      "true"
#cat == #cat   "true"
Doc 10, More Collections Slide # 7

Identity Problem

| phoneNumbers |
phoneNumbers := Dictionary new.
phoneNumbers
   at: 'whitney'
   put: '594-3535'.
phoneNumbers
   at: 'beck'
   put: '594-6807'.
phoneNumbers
   at: 'donald'
   put: '594-7248'.
   
phoneNumbers             "Returns 'Not Found' "
   keyAtValue: '594-3535' 
   ifAbsent: ['Not found']

keyAtValue:ifAbsent: compares values using ==


Doc 10, More Collections Slide # 8

Using Symbols

| phoneNumbers |
phoneNumbers := Dictionary new.
phoneNumbers
   at: 'whitney'
   put: '594-3535' asSymbol.
phoneNumbers
   at: 'beck'
   put: '594-6807' asSymbol.
phoneNumbers
   at: 'donald'
   put: '594-7248' asSymbol.
   
   
"This works"
phoneNumbers keyAtValue: '594-3535' asSymbol 
Doc 10, More Collections Slide # 9

Blocks and Returns

When a block evaluates a return (^) it exits the method the block was defined in

Example

Smalltalk.CS535 defineClass: #BlockExample
   superclass: #{Core.Object}
   etc
   
doExample
   Transcript 
      show: 'Start doExample';
      cr.
   self start.
   Transcript 
      show: 'End doExample';
      cr.!
   
evaluate: aBlock
   Transcript 
      show: 'Start evaluate';
      cr.
   aBlock value.
   Transcript 
      show: 'End evaluate';
      cr.!
   
start
   Transcript 
      show: 'Start start';
      cr.
   self evaluate: [^nil].
   Transcript 
      show: 'End start';
      cr.! !


Doc 10, More Collections Slide # 10

Running the Example
Evaluate:

BlockExample new doExample

The output in the Transcript is:

Start doExample
Start start
Start evaluate
End doExample

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