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What is mutableMapOf()?
The mutableMapOf() function is a part of the Kotlin standard library, crafted to create mutable maps. A mutable map is a collection of key-value pairs, akin to regular maps. However, with mutable maps, you can freely add, modify, or remove entries even after their initial creation.
Basic Syntax:
val mutableMap: MutableMap<KeyType, ValueType> = mutableMapOf(key1 to value1, key2 to value2, ...)Examples with Outputs
Constructing a Basic Mutable Map
val languages = mutableMapOf("JS" to "JavaScript", "PY" to "Python")
println(languages) // Output: {JS=JavaScript, PY=Python}Adding New Entries to the Map
val vehicles = mutableMapOf("C" to "Car", "B" to "Bike")
vehicles["T"] = "Truck"
println(vehicles) // Output: {C=Car, B=Bike, T=Truck}Removing Entries from the Map
val elements = mutableMapOf(1 to "Hydrogen", 2 to "Helium", 3 to "Lithium")
elements.remove(3)
println(elements) // Output: {1=Hydrogen, 2=Helium}Modifying Existing Map Entries
val grades = mutableMapOf("Alice" to 90, "Bob" to 75)
grades["Alice"] = 95
println(grades) // Output: {Alice=95, Bob=75}Checking If a Key Exists
val fruits = mutableMapOf("A" to "Apple", "B" to "Banana")
println("C" in fruits) // Output: falseClearing All Entries from the Map
val colors = mutableMapOf("R" to "Red", "G" to "Green", "B" to "Blue")
colors.clear()
println(colors) // Output: {}Convert a mutable map to an immutable one
val mutableData = mutableMapOf(1 to "One", 2 to "Two")
val immutableData = mutableData.toMap()Iterate over a mutableMapOf()
val pets = mutableMapOf("Dog" to "Bark", "Cat" to "Meow")
for ((animal, sound) in pets) {
println("$animal says $sound")
}
// Output:
// Dog says Bark
// Cat says MeowConclusion
mutableMapOf() shines in scenarios where the map's content needs to be dynamically changed, like adding or removing entries based on user input or real-time data. If your map doesn't require alterations post-creation, prefer mapOf() for immutability and associated benefits.
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