Kotlin - Map with Multiple Keys - Example

Today we will show you how to implement a  Map with Multiple Keys. 

• Solution 1: Using Kotlin Custom Key Class

• Solution 2: Using Google's Guava

• Solution 3: Using Apache Commons Collections 

Example 1: Using Kotlin Custom MultiMapKey 

Here we created a custom MultiMap Key class, we can use MultiMap as a Key to map a value.

object MultiKeyDemo {
    @JvmStatic
    fun main(args: Array<String>) {
        // Declaring the Map
        val table: MutableMap<MultiMapKey, String> = HashMap()
        // Declaring the key objects
        val key1 = MultiMapKey("raw1", "col1")
        val key2 = MultiMapKey("raw1", "col2")
        val key3 = MultiMapKey("raw1", "col3")
        // Putting the values
        table[key1] = "Java"
        table[key2] = "Kotlin"
        table[key3] = "Android"
        // Getting value by key
        val value2 = table[key2]
        println(value2)
        // Iterate map
        table.forEach { (k: MultiMapKey, v: String) ->
            println(
                "Key = "
                        + k + ", Value = " + v
            )
        }
        // Remove one item
        table.remove(key2)
    }
}
internal class MultiMapKey(var row: Any, var col: Any) {
    override fun hashCode(): Int {
        return row.hashCode() xor col.hashCode()
    }
    override fun equals(myKey: Any?): Boolean {
        return if (myKey is MultiMapKey) {
            val multiMapKey = myKey
            row == multiMapKey.row && col == multiMapKey.col
        } else {
            false
        }
    }
}

Example 2: Using Google's Guava

Maven Repository Link or Download the jar

Guava's Table is a collection that represents a table-like structure containing rows, columns and the associated cell values. The row and the column act as an ordered pair of keys.

import com.google.common.collect.HashBasedTable

import com.google.common.collect.Table

object GuavaMultiKeyDemo {

@JvmStatic

fun main(args: Array<String>) {

// Declaring the Table

val table: Table<String, String, String> = HashBasedTable.create()

// Insert & Update

table.put("raw1", "col1", "Java")

table.put("raw1", "col2", "Kotlin")

table.put("raw1", "col3", "Android")

// Getting the values

val value2 = table["raw1", "col3"]

println(value2)

}

}

Example 3: Using Apache Commons Collection

Maven Repository Link or Download the jar

The MultiKeyMap is the most efficient way to use multiple keys to map to a value. These provide get, containsKey, put and remove for individual keys which operate without extra object creation.

import org.apache.commons.collections4.map.MultiKeyMap

object ApacheMultiKeyDemo {

@JvmStatic

fun main(args: Array<String>) {

// Declaring the MultiKeyMap

val table = MultiKeyMap<String, String>()

// Insert & Update

table.put("raw1", "col1", "Java")

table.put("raw1", "col2", "Kotlin")

table.put("raw1", "col3", "Android")

// Getting the values

val value2 = table["raw1", "col2"]

println(value2)

// Contains key

val containsKey = table.containsKey("raw1", "col1")

println(containsKey)

}

}