Island Creator/Class: Ordered Collection

From Croquet Consortium

If your island (or game) will have an "inventory" or you need to "Save the game" or you need to have a score of the players etc. your island needs to access an external Database. We will have some lessons about SQL Database access from a Cobalt island but, to do this access, an Ordered Collection is an important intermediary resource.

For the creation of an Ordered Collection object we need to write the usual "new". Something like:

            |oC|
            oC := OrderedCollection new.

Like in the previous lesson, we have some mini-exercices to show all the methods working. Use the Workspace and Transcript windows inside the Cobalt environment.

add: 'x'

To add the string x after the last element of the collection.

addFirst: 'x'

To add the string x at the first position of the collection.

size

Returns the quantity of elements of the collection.

asString

Convert an element of the collection to String.

at:n

Returns the string in the position n.

Example

| oC |
oC:= OrderedCollection new.
oC add: 'Mary'.
oC addFirst: 'John'. 
oC add: 'Carl'.
1 to: oC size do: [
:i | i+1.  
Transcript show:   ((oC at: i),'\')withCRs . ]

IMPORTANT:Look how we did a loop reading all the elements of the collection. We have used the "formula" we have seeing in previous lesson:

1 to: "last" do: [
:i | i+1. 

"do something" 

 ]

We have used also two methods of the object String (an element of the OrderedCollection is an String object) to concatenate a '\' and to do the carriage return (like we have seen in the previous lesson)

Result

John
Mary
Carl

at:n put:'x'

Replace the element at the position n by the string 'x'

Example

| oC  |
oC:= OrderedCollection new.
oC add: 'John'.
oC add: 'Mary'.
oC add: 'Carl'.
oC at: 2 put: 'Peter'.
1 to: oC size do: [
:i | i+1.  
Transcript show:   ((oC at: i),'\')withCRs . ]

Result

John
Peter
Carl

add:'x' afterIndex: n

add:'x' after: 'y'

add:'x' before: 'y'

Example

| oC  |
oC:= OrderedCollection new.
oC add: 'John'.
oC add: 'Mary'.
oC add: 'Carl'.
oC add:'Peter' afterIndex: 1 .
oC add:'Hans' after: 'Mary' .
oC add:'Primo' before: 'John' .
1 to: oC size do: [
:i | i+1.  
Transcript show:   ((oC at: i),'\')withCRs . ].

Result

Primo
John
Peter
Mary
Hans
Carl

addAll: oC

Add the new Ordered Collection oC after this Ordered Collection.

addAllFirst: oC

Add the new Ordered Collection oC before this Ordered Collection.

Example

 | oC1 oC2 |
oC1 := OrderedCollection new.
oC1 add: 'John'.
oC1 add: 'Mary'.
oC1 add: 'Carl'.
oC2 := OrderedCollection new.
oC2 add: 'Hans'.
oC2 add: 'Peter'.
oC2 add: 'Andre'.

oC1 addAllFirst: oC2.
1 to: oC1 size do: [
:i | i+1.  
Transcript show:   ((oC1 at: i),'\')withCRs . ].

Result

Hans
Peter
Andre
John
Mary
Carl

copyFrom: i1 to: i2

Returns this Ordered Collection from the index i1 to i2. A new Ordered Collection.

Example

| oC1 oC2 |
oC1 := OrderedCollection new.
oC1 add: 'John'.
oC1 add: 'Mary'.
oC1 add: 'Carl'.

oC2:= oC1 copyFrom: 1 to: 2. 
 
1 to: oC2 size do: [
:i | i+1.  
Transcript show:   ((oC2 at: i),'\')withCRs . ].

Result

John
Mary

reversed

Returns this Ordered Collection having the elements in the reverse order.

Example

 | oC1 oC2 |
oC1 := OrderedCollection new.
oC1 add: 'John'.
oC1 add: 'Mary'.
oC1 add: 'Carl'.

oC2:= oC1 reversed. 
 
1 to: oC2 size do: [
:i | i+1.  
Transcript show:   ((oC2 at: i),'\')withCRs . ].

Result

Carl
Mary
John

removeAt: i

Removes the element at the index

Example

| oC  |
oC:= OrderedCollection new.
oC add: 'John'.
oC add: 'Mary'.
oC add: 'Carl'.
 oC removeAt: 2.
1 to: oC size do: [
:i | i+1.  
Transcript show:   ((oC at: i),'\')withCRs . ].

Result