// Java: Arrays.asList("a1", "a2", "a3") .stream() .findFirst() .ifPresent(System.out::println);
// 科特林: listOf("a1", "a2", "a3").firstOrNull()?.apply(::println)
或者,在名为ifPresent的String上创建扩展函数:
// 科特林: inline fun String?.ifPresent(thenDo: (String)->Unit) = this?.apply { thenDo(this) } // 现在使用新的扩展功能: listOf("a1", "a2", "a3").firstOrNull().ifPresent(::println)
另请参见:apply()功能
另请参阅:扩展功能
另请参阅:“ ?.安全呼叫”运算符和一般的可空性:http://stackoverflow.com/questions/34498562/in-kotlin-what-is-the-idiomatic-way-to-deal-with-nullable-values-referenceencing- o / 34498563#34498563