Retrieve Value by Key in HashMap in Kotlin | Kotlin HashMap get Function

The get function in Kotlin is used to retrieve the value associated with a specified key in a HashMap. This function is part of the Kotlin standard library and provides a convenient way to access values stored in a map.

Table of Contents

1. Introduction
2. get Function Syntax
3. Examples
   • Basic Usage
   • Handling Non-Existent Keys
4. Real-World Use Case
5. Conclusion

Introduction

The get function allows you to retrieve the value associated with a specified key in a HashMap. If the key is present in the map, the function returns the corresponding value. If the key is not present, the function returns null.

get Function Syntax

The syntax for the get function is as follows:

operator fun <K, V> Map<K, V>.get(key: K): V?

Parameters:

• key: The key whose associated value is to be returned.

Returns:

• V?: The value associated with the specified key, or null if the key is not present in the map.

The get function retrieves the value associated with the specified key. If the key is not found, the function returns null. This behavior allows you to check for the existence of a key and handle cases where the key is not present.

Examples

Basic Usage

To demonstrate the basic usage of get, we will create a HashMap and retrieve values associated with specific keys.

Example

fun main() {
    val map = hashMapOf(
        "Alice" to 30,
        "Bob" to 25,
        "Charlie" to 35
    )
    val aliceAge = map["Alice"]
    val bobAge = map["Bob"]
    println("Alice's age: $aliceAge")
    println("Bob's age: $bobAge")
}

Output:

Alice's age: 30
Bob's age: 25

Handling Non-Existent Keys

This example shows how to handle cases where the key is not present in the map.

Example

fun main() {
    val map = hashMapOf(
        "Alice" to 30,
        "Bob" to 25,
        "Charlie" to 35
    )
    val davidAge = map["David"]
    if (davidAge != null) {
        println("David's age: $davidAge")
    } else {
        println("David is not in the map.")
    }
}

Output:

David is not in the map.

Real-World Use Case

Retrieving User Information

In real-world applications, the get function can be used to retrieve user information stored in a HashMap.

Example

data class User(val id: Int, val name: String, val email: String)

fun main() {
    val userMap = hashMapOf(
        1 to User(1, "Alice", "alice@example.com"),
        2 to User(2, "Bob", "bob@example.com"),
        3 to User(3, "Charlie", "charlie@example.com")
    )

    val userIdToCheck = 2
    val user = userMap[userIdToCheck]

    if (user != null) {
        println("User details: $user")
    } else {
        println("User with ID $userIdToCheck is not in the map.")
    }
}

Output:

User details: User(id=2, name=Bob, email=bob@example.com)

Conclusion

The get function in Kotlin is a simple and effective way to retrieve values associated with keys in a HashMap. It allows you to access values stored in a map and handle cases where keys are not present, making it useful for various applications, including data retrieval and user information management. 

By understanding and using the get function, you can effectively manage and manipulate HashMap collections in your Kotlin applications.