Greetings, student! Today, we're studying the Map data structure in Kotlin. It functions like a dictionary, pairing a unique key with a corresponding value. Our primary focus will be on creating, accessing, and utilizing the unique properties of Maps in Kotlin.
In Kotlin, a Map stores key-value entries. Consider a dictionary, where words are keys, and definitions are values. This analogy parallels a Map's functioning: keys are unique, just as no two words share the same meaning.
Kotlin1fun main() { 2 val animalHabitats = mapOf("Lion" to "Savannah", "Penguin" to "Antarctica", "Kangaroo" to "Australia") 3 println(animalHabitats) // prints {Lion=Savannah, Penguin=Antarctica, Kangaroo=Australia} 4}
In Kotlin, mapOf() and mutableMapOf() are functions designed for creating Maps, collections of key-value pairs. For mutable maps, you can insert or modify a key-value pair using the syntax map[<key>] = <value>. Modifying an existing key updates its associated value.
Kotlin1fun main() { 2 val immutableMap = mapOf("Sam" to 23, "Amanda" to 30, "Trevor" to 29) 3 println(immutableMap) // prints {Sam=23, Amanda=30, Trevor=29} 4 5 val mutableMap = mutableMapOf("Mary" to 31, "Bob" to 28, "Hannah" to 27) 6 mutableMap["Roman"] = 27 // Adding a new key-value pair 7 mutableMap["Bob"] = 29 // Bob's age is updated to 29 8 println(mutableMap) // prints {Mary=31, Bob=29, Hannah=27, Roman=27} 9}
This example demonstrates not only how to define immutable and mutable maps but also how to dynamically add elements to mutable maps and modify existing entries.
We access values in Maps via their keys. To add or remove elements, we respectively use the put() and remove() functions.
Kotlin1fun main() { 2 val namesToAges = mapOf("Sam" to 23, "Amanda" to 30, "Trevor" to 29) 3 println(namesToAges["Amanda"]) // prints 30 4 5 val mutableNamesToAges = mutableMapOf("Sam" to 23, "Amanda" to 30) 6 mutableNamesToAges.put("Trevor", 29) 7 println(mutableNamesToAges) // prints {Sam=23, Amanda=30, Trevor=29} 8 9 mutableNamesToAges.remove("Sam") 10 println(mutableNamesToAges) // prints {Amanda=30, Trevor=29} 11}
Maps offer useful properties. size denotes the number of entries, keys returns all keys, and values list all values present in a Map.
Kotlin1fun main() { 2 val namesToAges = mapOf("Sam" to 23, "Amanda" to 30, "Trevor" to 29) 3 println(namesToAges.size) // prints 3 4 println(namesToAges.keys) // prints [Sam, Amanda, Trevor] 5 println(namesToAges.values) // prints [23, 30, 29] 6 7 val emptyMap = mapOf<String, Int>() // Here we're defining a map where keys are strings and values are integers 8 println(emptyMap.isEmpty()) // prints true 9}
Brilliant! You've explored Maps in Kotlin and understood how to create, manage, and delve into their properties. This knowledge prepares you for the practice sessions ahead, reinforcing these concepts. Keep going!