kotlin lambda表達式簡單示例

測試一

class Test1 {

    @Test
    fun test1() {
        val list = mutableListOf(1, 2, 3)
        val max1 = maxTest(list) { a, b -> less(a, b) } //推薦寫法
        val max2 = maxTest(list, { a, b -> less(a, b) })
        println("===========================================$max1")
        println("===========================================$max2")
    }

    fun less(t1: Int, t2: Int): Boolean {
        return t1 < t2
    }

    /**
     *  擷取最大值
     *  (T, T) -> Boolean  : lambda表達式當作參數
     */
    fun <T> maxTest(collection: Collection<T>, less: (T, T) -> Boolean): T? {
        var max: T? = null
        for (it in collection)
            if (max == null || less(max, it))
                max = it
        return max
    }
}


           

測試2

class Test2 {

    @Test
    fun Test21() {
        val age = 18
        val name = "xq"
        ifNotNull(age, name, { age, name -> getStudentAge(age, name) })
        println("======================================================================")

        ifNotNullString(age, name, { age, name -> getStudentName(age, name) })
        println("======================================================================")

        //kotlin 預設協定 有lambda式的 可以變為如下格式，普通參數用小括号 lambda 用大括号隔開
        ifNotNullString(age, name) { age, name -> getStudentName(age, name) }
    }


    /**
     * 泛型有傳回值
     */
    fun getStudentName(age: Int?, name: String?): String {
        println("age=${age},name=${name}" + "jack")
        return "jack"
    }

    /**
     * 泛型無傳回值
     */
    fun getStudentAge(age: Int?, name: String?) {
        println("age=${age},name=${name}")
    }

    /**
     * (1)傳遞參數為lambda表達式；無參傳回
     * (2)泛型的寫法；
     */
    fun <T1, T2> ifNotNull(value1: T1?, value2: T2?, bothNotNull: (T1, T2) -> (Unit)) {
        if (value1 != null && value2 != null) {
            bothNotNull(value1, value2)
        }
    }

    /**
     * (1)傳遞參數為lambda表達式；有參傳回
     * (2)泛型的寫法；
     */
    fun <T1, T2> ifNotNullString(value1: T1?, value2: T2?, bothNotNull: (T1, T2) -> (String)) {
        if (value1 != null && value2 != null) {
            bothNotNull(value1, value2)
        }
    }

}