kotlin,null let expression

淩亂°似流年 2023-09-27 19:34 1阅读 0赞

class Num {
        var data: Int? = -1
    }
    
    fun main(args: Array<String>) {
        val n = Num()
        n.data = null
    
        var b = true
    
        b = n.data?.let { it > 0 } ?: false
        println(b)
    
        n.data = 1
        b = n.data?.let { it > 0 } ?: false
        println(b)
    }

> false  
> true

[kotlin常用表达式let，?:，as?，?.，!!\_zhangphil的博客-CSDN博客it.todo() //函数内使用it替代object对象访问属性和方法。it.todo() //object不为null，才会执行let函数。当a不为null时,执行大括号里的语句（it肯定不为null）如果a == null ,则为 null。= null，则a.b()如果 a 不是 b，则为 null。如果a 是 b，则 a as b。当a为null时，什么都不执行。如果a==null，抛出空指针。=null时，执行a。当a==null时，执行b。![favicon32.ico][]https://blog.csdn.net/zhangphil/article/details/129264159][kotlin_let_as_._zhangphil_-CSDN_it.todo_ _it_object_it.todo_ _object_null_let_a_null_it_null_a _ null _ null_ null_a.b_ a _ b_ null_a _ b_ a as b_a_null_a_null_null_a_a_null_b_favicon32.ico_https_blog.csdn.net_zhangphil_article_details_129264159]

[kotlin的let，with，run，apply，also，异同区别\_zhangphil的博客-CSDN博客it.todo() //object不为null，才会执行let函数。当a不为null时,执行大括号里的语句（it肯定不为null）如果a == null ,则为 null。= null，则a.b()如果 a 不是 b，则为 null。如果a 是 b，则 a as b。当a为null时，什么都不执行。如果a==null，抛出空指针。=null时，执行a。当a==null时，执行b。kotlin常用表达式let，?zhang 19 工作 996，赚59760。zhang 20 工作 996，赚59760。![favicon32.ico][]https://blog.csdn.net/zhangphil/article/details/129327285][kotlin_let_with_run_apply_also_zhangphil_-CSDN_it.todo_ _object_null_let_a_null_it_null_a _ null _ null_ null_a.b_ a _ b_ null_a _ b_ a as b_a_null_a_null_null_a_a_null_b_kotlin_let_zhang 19 _ 996_59760_zhang 20 _ 996_59760_favicon32.ico_https_blog.csdn.net_zhangphil_article_details_129327285]

[favicon32.ico]: https://g.csdnimg.cn/static/logo/favicon32.ico
[kotlin_let_as_._zhangphil_-CSDN_it.todo_ _it_object_it.todo_ _object_null_let_a_null_it_null_a _ null _ null_ null_a.b_ a _ b_ null_a _ b_ a as b_a_null_a_null_null_a_a_null_b_favicon32.ico_https_blog.csdn.net_zhangphil_article_details_129264159]: https://blog.csdn.net/zhangphil/article/details/129264159
[kotlin_let_with_run_apply_also_zhangphil_-CSDN_it.todo_ _object_null_let_a_null_it_null_a _ null _ null_ null_a.b_ a _ b_ null_a _ b_ a as b_a_null_a_null_null_a_a_null_b_kotlin_let_zhang 19 _ 996_59760_zhang 20 _ 996_59760_favicon32.ico_https_blog.csdn.net_zhangphil_article_details_129327285]: https://blog.csdn.net/zhangphil/article/details/129327285