kotlin 高阶函数用法

继续测试下kotlin常用高阶函数用法，也就是有参数是函数的函数：

private fun testOthers() { val numbers = listOf(1, 2, 3, 4, 5) val evenNumbers = numbers.filter { it % 2 == 0 } val doubledNumbers = numbers.map { it * 2 } println("zxzx, numbers: $numbers") println("zxzx, evenNumbers: $evenNumbers") println("zxzx, doubledNumbers: $doubledNumbers") val numbers2 = listOf("1", "2", "灭绝师太", "3", "周芷若") val validNumbers = numbers2.mapNotNull { it.toIntOrNull() } // 字符串转换数字，过滤空值 println("zxzx, validNumbers: $validNumbers") // 扁平化嵌套集合 val lists = listOf(listOf("i", "always"), listOf("love"), listOf("vicky", "du"), listOf("!")) val result = lists.flatMap { it } println("zxzx, $result") data class User(val name: String, val hobbies: List<String>) val users = listOf( User("vicky du", listOf("网购", "凉皮面", "鸭血粉丝", "摄影", "八卦", "户外活动")), User("daling zhou", listOf("户外活动", "编程", "花生", "打游戏", "刷美女")) ) val allHobbies = users.flatMap { it.hobbies } // 从对象中提取嵌套集合 println("zxzx, $allHobbies") data class MeiNv(val name: String, val age: Int) // 美人 val meiNvs = listOf<MeiNv>(MeiNv("西施", 18), MeiNv("貂蝉", 16) , MeiNv("陈圆圆", 17), MeiNv("灭绝师太", 38), MeiNv("苏小妹", 15)) val result1 = meiNvs.takeWhile { it.age < 30 }.dropWhile { it.age < 16 } // 筛选条件 println("zxzx, 选美结果为：") result1.forEach { println("zxzx, ${it.name}")} // 使用 reduce 计算总和 val sum = listOf(1, 2, 3, 4, 5).reduce { acc, value -> acc + value } println("zxzx, sum = $sum") // reduce函数计算最大值 println("zxzx, max: ${listOf(1, 2, 3, 4, 5).reduce { acc, value -> if (acc > value) acc else value }}") // 字符串拼接 println("zxzx, ${listOf("司马懿:", " ", "听诸葛亮弹琴，如观其肺腑也。").reduce { acc, word -> acc + word }}") }

打印：

ok. 用起来很灵活，很方便。