This topic is about Scala Collections – ListMap.
Scala map is a collection of key/value pairs. Any value can be retrieved based on its key. Keys are unique in the Map, but values need not be unique. ListMap implements immutable map and uses list to implement the same. It is used with small number of elements.
Declaring ListMap Variables
The following is the syntax for declaring an ListMap variable.
Syntax
val colors = ListMap("red" -> "#FF0000", "azure" -> "#F0FFFF", "peru" -> "#CD853F")
Here, colors is declared as an hash-map of Strings, Int which has three key-value pairs. Values can be added by using commands like the following −
Command
var myMap1: ListMap[Char, Int] = colors + ("black" -> "#000000");
Processing ListMap
Below is an example program of showing how to create, initialize and process ListMap −
Example
import scala.collection.immutable.ListMap
object Demo {
def main(args: Array[String]) = {
var myMap: ListMap[String,String] = ListMap(
"red" -> "#FF0000", "azure" -> "#F0FFFF", "peru" -> "#CD853F"
);
// Add an element
var myMap1: ListMap[String,String] = myMap + ("white" -> "#FFFFFF");
// Print key values
myMap.keys.foreach{
i =>
print( "Key = " + i )
println(" Value = " + myMap(i) )
}
if( myMap.contains( "red" )) {
println("Red key exists with value :" + myMap("red"))
} else {
println("Red key does not exist")
}
if( myMap.contains( "maroon" )) {
println("Maroon key exists with value :" + myMap("maroon"))
} else {
println("Maroon key does not exist")
}
//removing element
var myMap2: ListMap[String,String] = myMap - ("white");
// Create empty map
var myMap3: ListMap[String,String] = ListMap.empty[String, String];
println(myMap1);
println(myMap2);
println(myMap3);
}
}
Save the above program in Demo.scala. The following commands are used to compile and execute this program.
Command
\>scalac Demo.scala \>scala Demo
Output
Key = red Value = #FF0000 Key = azure Value = #F0FFFF Key = peru Value = #CD853F Red key exists with value :#FF0000 Maroon key does not exist ListMap(red -> #FF0000, azure -> #F0FFFF, peru -> #CD853F, white -> #FFFFFF) ListMap(red -> #FF0000, azure -> #F0FFFF, peru -> #CD853F) ListMap()
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