Kotlin 常用语法糖完整整理

Kotlin 实用语法糖整理

1. 属性访问

class Person {var name: String = ""  // 自动生成 getter/setterval age: Int = 25      // 只读属性，仅生成 getter
}

2. 空安全操作

val length = name?.length        // 安全调用
val length = name?.length ?: 0   // 空值替代
val length = name!!.length       // 强制非空

3. 字符串模板

val name = "Kotlin"
val message = "Hello, $name!"            // 变量引用
val message2 = "Length: ${name.length}"  // 表达式引用

4. 集合操作

val numbers = listOf(1, 2, 3, 4, 5)
val doubled = numbers.map { it * 2 }     // 映射
val evens = numbers.filter { it % 2 == 0 } // 过滤
val sum = numbers.reduce { acc, num -> acc + num } // 归约
val first = numbers.find { it > 3 }      // 查找首个
val exists = numbers.any { it > 3 }      // 存在性检查
val all = numbers.all { it > 0 }         // 全量检查

5. 扩展函数

fun String.addExclamation() = "$this!"
val result = "Hello".addExclamation()  // 输出: "Hello!"

6. 数据类

data class Person(val name: String, val age: Int)
val person = Person("Alice", 25)
val copy = person.copy(age = 26)  // 复制修改

7. 智能类型转换

fun demo(x: Any) {if (x is String) {println(x.length)  // 自动转为String}
}

8. when表达式

val result = when (x) {1 -> "One"2 -> "Two"else -> "Other"
}val status = when {age < 18 -> "未成年"age < 60 -> "成年"else -> "老年"
}

9. 解构声明

val (name, age) = Person("Alice", 25)
for ((k, v) in map) {println("$k: $v")
}

10. Lambda表达式

val sum = { x: Int, y: Int -> x + y }
list.forEach { println(it) }
with(person) {println(name)println(age)
}

11. 作用域函数

person.let { println(it.name) }  // let
with(person) { println(name) }   // with
person.apply { name = "Bob" }    // apply
person.run { "$name is $age" }   // run

12. 集合链式操作

val result = list.filter { it > 2 }.map { it * 2 }.take(2).sum()

13. 参数默认值

fun greet(name: String, greeting: String = "Hello") {println("$greeting, $name!")
}
greet("Alice")                    // 默认参数
greet("Bob", greeting = "Hi")     // 命名参数

14. 单例与伴生对象

object Singleton {fun action() = "Hello"
}class MyClass {companion object {fun create() = MyClass()}
}

15. 属性委托

class Example {var p: String by Delegate()val lazyVal by lazy { "计算值" }
}

16. 内联函数

inline fun measureTime(action: () -> Unit): Long {val start = System.currentTimeMillis()action()return System.currentTimeMillis() - start
}

17. 密封类

sealed class Result {data class Success(val data: String) : Result()data class Error(val msg: String) : Result()
}

18. 协程基础

suspend fun fetchData(): String {delay(1000)return "数据"
}CoroutineScope(Dispatchers.IO).launch {val data = fetchData()withContext(Dispatchers.Main) {updateUI(data)}
}

19. 委托实现

class Delegate {private var value = ""operator fun getValue(thisRef: Any?, prop: KProperty<*>): String = valueoperator fun setValue(thisRef: Any?, prop: KProperty<*>, newValue: String) {value = newValue}
}

20. 运算符重载

data class Point(val x: Int, val y: Int) {operator fun plus(other: Point) = Point(x + other.x, y + other.y)
}
val p = Point(1, 2) + Point(3, 4)  // Point(4, 6)

21. 中缀表达式

infix fun Int.times(str: String) = str.repeat(this)
val res = 3 times "Hi "  // "Hi Hi Hi "

22. 尾递归优化

tailrec fun factorial(n: Int, acc: Int = 1): Int {return if (n <= 1) acc else factorial(n - 1, n * acc)
}

23. 类型别名

typealias StringList = List<String>
typealias Predicate<T> = (T) -> Boolean

24. 内联类

inline class Password(val value: String) {fun isValid() = value.length >= 8
}

25. 协程作用域

runBlocking {delay(1000)println("完成")
}suspend fun fetch() = coroutineScope {val d1 = async { fetch1() }val d2 = async { fetch2() }d1.await() + d2.await()
}

26. 集合构建

val list = buildList {add("第一项")add("第二项")addAll(listOf("第三", "第四"))
}

27. 序列操作

val seq = sequence {yield(1)yield(2)yield(3)
}

28. 反射注解

@Target(AnnotationTarget.CLASS)
@Retention(AnnotationRetention.RUNTIME)
annotation class MyAnnotation(val value: String)

29. DSL构建

class HTMLBuilder {fun head(init: Head.() -> Unit) = Head().apply(init)
}

29. DSL (领域特定语言)

class HTMLBuilder {fun head(init: Head.() -> Unit) = Head().apply(init)fun body(init: Body.() -> Unit) = Body().apply(init)
}

30. 委托属性 - 内置实现

class Example {val lazyValue: String by lazy { "耗时计算" }var name: String by Delegates.observable("") { _, old, new ->println("$old -> $new")}var age: Int by Delegates.vetoable(0) { _, _, new ->new >= 0}
}

31. 扩展属性

val String.lastChar: Charget() = this[length - 1]val String.isPalindrome: Booleanget() = this == reversed()

32. 高阶函数与函数类型

typealias Operation = (Int, Int) -> Intfun calculate(a: Int, b: Int, operation: Operation) = operation(a, b)val add: Operation = { a, b -> a + b }
val result = calculate(5, 3, add)  // 8

33. 协程通道

fun CoroutineScope.produceNumbers() = produce<Int> {repeat(5) { x ->send(x + 1)}
}

34. 内联函数与具体化类型

inline fun <reified T> createInstance() = T::class.java.getDeclaredConstructor().newInstance()

35. 集合扩展函数

val list = listOf(1, 2, 3, 4, 5)
list.isNotEmpty()      // true
list.isEmpty()         // false
list.all { it > 0 }    // true
list.any { it > 3 }    // true
list.none { it > 10 }  // true
list.count { it % 2 == 0 } // 2

36. 字符串扩展函数

val text = "  Hello World  "
text.trim()            // "Hello World"
text.isBlank()         // false
text.isNotBlank()      // true
text.uppercase()       // "  HELLO WORLD  "
text.lowercase()       // "  hello world  "

37. 集合分组操作

val list = listOf(1, 2, 3, 4, 5)
val grouped = list.groupBy { it % 2 == 0 }
val (even, odd) = list.partition { it % 2 == 0 }

38. 集合类型转换

val list = listOf(1, 2, 3, 4, 5)
list.toSet()           // Set<Int>
list.associate { it to it * 2 } // {1=2, 2=4, 3=6, 4=8, 5=10}

39. 集合查询操作

val list = listOf(1, 2, 3, 4, 5)
list.find { it > 3 }    // 4
list.firstOrNull { it > 3 } // 4
list.random()           // 随机元素

40. 集合排序去重

val list = listOf(3, 1, 4, 1, 5, 9, 2, 6)
list.sorted()          // [1, 1, 2, 3, 4, 5, 6, 9]
list.distinct()        // [3, 1, 4, 5, 9, 2, 6]

41. 集合窗口操作

val list = listOf(1, 2, 3, 4, 5)
list.windowed(3)       // [[1, 2, 3], [2, 3, 4], [3, 4, 5]]
list.chunked(2)        // [[1, 2], [3, 4], [5]]

42. 集合聚合操作

val list = listOf(1, 2, 3, 4, 5)
list.sum()             // 15
list.average()         // 3.0
list.minOrNull()       // 1
list.maxOrNull()       // 5

43. 字符串操作扩展

val text = "Hello World"
text.first()           // 'H'
text.last()            // 'd'
text.substring(0, 5)   // "Hello"
text.replace("World", "Kotlin") // "Hello Kotlin"

44. 集合比较操作

val list1 = listOf(1, 2, 3)
val list2 = listOf(1, 2, 3)
list1 == list2         // true
list1.contentEquals(list2) // true

总结

这就是 Kotlin 最常用的语法糖完整整理！这些特性让 Kotlin 代码更简洁、更安全、更易读。

主要优势：

- **空安全**：避免空指针异常
- **函数式编程**：更简洁的集合操作
- **扩展函数**：为现有类添加功能
- **数据类**：自动生成常用方法
- **协程**：简化异步编程
- **委托属性**：减少样板代码
- **作用域函数**：更清晰的代码结构

使用建议：

1. 优先使用 Kotlin 的语法糖，减少样板代码
2. 合理使用空安全操作符，避免空指针异常
3. 善用扩展函数，提高代码可读性
4. 使用数据类简化模型类
5. 利用协程简化异步编程
6. 使用作用域函数让代码更清晰