When trying to get an element at specified index, exception may be thrown if index is out of bounds. To avoid this exception, we can use the following function :

• getOrNull() : returns the element at specified index (if found) or null (if not found).
• getOrElse() : returns the element at specified index (if found) or executes the given code block (if not found).

 // Syntax :
coll.getOrNull()
coll.getOrNull() ?: /* Default value */
coll.getOrElse() { /* Code to execute, return default value */ }
 

Example :

 fun main() {
    val nums = listOf(1, 2, 3)
    
    // typeof x = Int?
    val x = nums.getOrNull(3)
    
    // typeof y = Int (Default value provided)
    val y = nums.getOrNull(3) ?: -1
    
    // typeof z = Int (Default value provided)
    val z = nums.getOrElse(3) {
        println("z: nums[$it] not found!")
        0 // Default value
    }
    
    println("""
        x = $x
        y = $y
        z = $z
    """.trimIndent())
}

/* Output :
z: nums[3] not found!
x = null
y = -1
z = 0 */
 

When looking up for a key in Map, we get a nullable result. The returned value is null when given key is not found in the map :

 val map = mapOf(
    "A" to 1, "B" to 2, "C" to 3
)
val a = map["A"] // Type : Int?
 

To avoid nullable return type & properly handle not found case, we can use the following functions :

• getOrDefault() : returns the value associated with given key (if found) or the default value provided (if not found)
• getOrElse() : returns the value associated with given key (if found) or executes the given code block (if not found).

 map.getOrDefault(/* key */, /* Default Value */)
map.getOrElse(/* key */) { /* Code to execute, return default value */ }
 

Example :

 fun main() {
    val map = mapOf(
        "A" to 1, "B" to 2, "C" to 3
    )
    
    val a = map["A"] // Type : Int?
    
    val b = map.getOrDefault("B", -1) // Type : Int
    
    val d = map.getOrElse("D") {
        println("D not found!")
        -1 // Default value
    }
    
    println("""
        a = $a
        b = $b
        d = $d
    """.trimIndent())
}

/* Output :

D not found!
a = 1
b = 2
d = -1 */