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How to iterate over a HashMap in Kotlin

How to iterate over a HashMap in Kotlin.

Here's a detailed step-by-step tutorial on how to iterate over a HashMap in Kotlin:

Step 1: Create a HashMap​

To begin, you need to create a HashMap in Kotlin. The HashMap is a collection that stores key-value pairs. You can define a HashMap using the mutableMapOf() function. For example:

val hashMap = mutableMapOf<String, Int>()

Here, we have created a HashMap named hashMap that stores keys of type String and values of type Int.

Step 2: Add elements to the HashMap​

Next, you can add elements to the HashMap using the put() function. The put() function takes two arguments: the key and the value. For example:

hashMap.put("Apple", 10)
hashMap.put("Orange", 15)
hashMap.put("Banana", 20)

Here, we have added three key-value pairs to the HashMap.

Step 3: Iterate over the HashMap using for loop​

To iterate over the HashMap, you can use a for loop in Kotlin. The for loop iterates over each key in the HashMap, and you can access the corresponding value using the key. For example:

for ((key, value) in hashMap) {
    println("Key: $key, Value: $value")
}

This code will iterate over each key-value pair in the HashMap and print the key and value.

Step 4: Iterate over the HashMap using iterator()​

Alternatively, you can use the iterator() function to iterate over the HashMap. The iterator() function returns an iterator that allows you to loop over the keys and values. Here's an example:

val iterator = hashMap.iterator()
while (iterator.hasNext()) {
    val entry = iterator.next()
    val key = entry.key
    val value = entry.value
    println("Key: $key, Value: $value")
}

In this code, we get an iterator from the HashMap and use a while loop to iterate over the keys and values. We access the key and value using the key and value properties of the iterator's entry.

Step 5: Iterate over the HashMap keys or values only​

If you only need to iterate over the keys or values of the HashMap, you can use the keys or values properties. Here's an example:

// Iterate over keys
for (key in hashMap.keys) {
    println("Key: $key")
}

// Iterate over values
for (value in hashMap.values) {
    println("Value: $value")
}

In these examples, we use a for loop to iterate over the keys or values of the HashMap. We can access each key or value directly without the need for a separate iterator.

That's it! You have now learned how to iterate over a HashMap in Kotlin. You can use the for loop, iterator(), keys, or values properties depending on your specific requirements.