Introduction

A List can hold numbers, words or really anything. That’s why we call the List generic.

Generics are basically used to define which types a class can hold and which type an object currently holds.

Syntax

• class ClassName<TypeName>
• class ClassName<*>
• ClassName<in UpperBound>
• ClassName<out LowerBound>
• class Name<TypeName:UpperBound>

Parameters

| Parameter | Details | | ––––––– | —————————— | | TypeName | Type Name of generic parameter | | UpperBound | Covariant Type | | LowerBound | Contravariant Type | | ClassName | Name of the class |

Remarks

Implied Upper Bound is Nullable

In Kotlin Generics, the upper bound of type parameter T would be Any?. Therefore for this class:

class Consumer<T>

The type parameter T is really T: Any?. To make a non-nullable upper bound, explicitly specific T: Any. For example:

class Consumer<T: Any>