Kotlin变量与数据类型详解

val name = "Kotlin"   // 类型推断为 String
var age = 25          // 类型推断为 Int

// name = "Java"      // 编译错误：Val cannot be reassigned
age = 26              // 合法操作

val score: Double = 95.5
var isStudent: Boolean = true

val numInt: Int = 100
val numLong: Long = numInt.toLong()  // 正确
// val numLong: Long = numInt       // 错误

val isTrue: Boolean = true
val isAdult = age >= 18  // 推断为 Boolean

val letter: Char = 'A'
val unicodeChar = '\u0041'  // 'A'

// 普通字符串
val message = "Hello, $name! Age is ${age + 1}"

// 多行文本
val text = """
    First line
    Second line
     Third line
""".trimIndent()

// 创建方式1：arrayOf
val numbers = arrayOf(1, 2, 3)

// 创建方式2：工厂函数
val zeros = Array(3) { 0 }  // [0, 0, 0]

// 访问元素
println(numbers[0])  // 输出 1

val intArray: IntArray = intArrayOf(1, 2, 3)
val charArray = charArrayOf('a', 'b', 'c')

val anyValue: Any = 42  // 可接受任意类型

fun printMessage(): Unit {
    println("This returns Unit")
}

fun fail(): Nothing {
    throw RuntimeException("Error occurred")
}

when (val obj: Any = "Kotlin") {
    is String -> println(obj.length)  // 自动转换为 String
    is Int -> println(obj + 1)
}

val str: String? = "123"
val num: Int? = str as? Int  // 安全转换，失败返回 null