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HashMap in Scala

HashMap is a collection based on maps and hashes. In this tutorial on Scala HashMap, we will learn about HashMap and operations on them.
Submitted by Shivang Yadav, on December 24, 2019

Scala HashMap

HashMap is a collection based on maps and hashes. It stores key-value pairs.

Denoted by:

    HashMap<Key, Value> or HashMap<K, V>

Syntax:

    var hashmap = HashMap("key1" -> "value1", ...);

To import HashMap to our Scala program, the following statement is used,

    scala.collection.mutable.HashMap

Now, let's see the operations on HashMap in Scala,

Example 1: Creating HashMap in Scala

Creating a HashMap in Scala is an easy process. A HashMap in Scala can be empty also.

import scala.collection.mutable.HashMap 

object MyClass {
    def main(args: Array[String]) {
        var hashmap = new HashMap()
        var hashmap2 = HashMap(1 -> "K1200" , 2 -> "Thunderbird 350", 3 -> "CBR 1000")
        println("Empty HashMap : "+hashmap)
        println("Hashmap with elements : "+hashmap2)
    }
}

Output

Empty HashMap : HashMap()
Hashmap with elements : HashMap(1 -> K1200, 2 -> Thunderbird 350, 3 -> CBR 1000)

Example 2: Accessing elements of HashMap

The elements of a HashMap can be accessed in Scala using foreach loop as shown below,

import scala.collection.mutable.HashMap 

object MyClass {
    def main(args: Array[String]) {
        var hashmap = HashMap(1 -> "K1200" , 2 -> "Thunderbird 350", 3 -> "CBR 1000")
        hashmap.foreach  
        {   
            case (key, value) => println (key + " -> " + value)          
        }   
    }
}

Output

1 -> K1200
2 -> Thunderbird 350
3 -> CBR 1000

Example 3: Adding elements to the HashMap

Adding of elements to the HashMap can also be done in Scala programming language. The + operator is used to add new key-value pair to the HashMap.

import scala.collection.mutable.HashMap 

object MyClass {
    def main(args: Array[String]) {
        var hashmap = HashMap(1 -> "K1200" , 2 -> "Thunderbird 350", 3 -> "CBR 1000")
        println("The HashMap is : "+hashmap)
        println("Adding new elements to the HashMap. ")
        hashmap += (7 -> "HD Fat Boy")
        println("The HashMap is : "+hashmap)
    }
}

Output

The HashMap is : HashMap(1 -> K1200, 2 -> Thunderbird 350, 3 -> CBR 1000)
Adding new elements to the HashMap. 
The HashMap is : HashMap(1 -> K1200, 2 -> Thunderbird 350, 3 -> CBR 1000, 7 -> HD Fat Boy)

Example 4: Removing element from HashMap in Scala

In Scala removing elements from a HashMap is also possible. The - operator is used to remove elements from HashMap.

import scala.collection.mutable.HashMap 

object MyClass {
    def main(args: Array[String]) {
        var hashmap = HashMap(1 -> "K1200" , 2 -> "Thunderbird 350", 3 -> "CBR 1000")
        println("The HashMap is : "+hashmap)
        println("removing elements to the HashMap. ")
        hashmap -= 3
        println("The HashMap is : "+hashmap)
    }
}

Output

The HashMap is : HashMap(1 -> K1200, 2 -> Thunderbird 350, 3 -> CBR 1000)
removing elements to the HashMap. 
The HashMap is : HashMap(1 -> K1200, 2 -> Thunderbird 350)