Kotlin Idioms：提升代码质量与开发效率的秘诀

Create DTOs (POJOs/POCOs)

data class Customer(val name: String, val email: String)

provides a Customer class with the following functionality:

• getters (and setters in case of vars) for all properties
• equals()
• hashCode()
• toString()
• copy()
• component1(), component2(), …, for all properties (see Data classes)

Default values for function parameters

fun foo(a: Int = 0, b: String = "") {
   
    ... }

Filter a list

val positives = list.filter {
   
    x -> x > 0 }

Or alternatively, even shorter:

val positives = list.filter {
   
    it > 0 }

Learn the difference between Java and Kotlin filtering.

Check the presence of an element in a collection

if ("john@example.com" in emailsList) {
   
    ... }

if ("jane@example.com" !in emailsList) {
   
    ... }

String interpolation

println("Name $name")

Learn the difference between Java and Kotlin string concatenation.

Instance checks

when (x) {
   
   
    is Foo -> ...
    is Bar -> ...
    else   -> ...
}

Read-only list

val list = listOf("a", "b", "c")

Read-only map

val map = mapOf("a" to 1, "b" to 2, "c" to 3)

Access a map entry

println(map["key"])
map