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


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


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)
}
}

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