【kotlin】Kotlin笔记14-延迟初始化和密封类(lateinit,sealed)

淩亂°似流年 2022-11-17 05:08 153阅读 0赞

### Kotlin笔记14-延迟初始化和密封类 ###

**8.1 延迟初始化和密封类**

*  **延迟初始化**

> **lateinit:** 针对编译器

`Example:`

private var adapter: MsgAdapter? = null
    //优化->
    private lateinit var adapter : MsgAdapter

*判断一个变量是否完成了初始化*

if(!::adapter.isInitialized){
    	adapter = MsgAdapter(msgList)
    }

<table> 
 <thead> 
  <tr> 
   <th>序号</th> 
   <th>Tips</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>::adapter.isInitialized固定写法</td> 
   <td>判断adapter是否进行初始化</td> 
  </tr> 
 </tbody> 
</table>

--------------------

*  **密封类**

`Example:`

interface Result
    class Success(val msg:String):Result
    class Failure(val error:Exception):Result
    
    fun getResultMsg(result: Result)=when(result){
        is Success->result.msg
        is Failure->result.error.message
        else -> throw IllegalArgumentException()//这里
    }

<table> 
 <thead> 
  <tr> 
   <th>序号</th> 
   <th>Tips</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>1</td> 
   <td>为了满足编译器要求而去编写无用条件分支</td> 
  </tr> 
 </tbody> 
</table>

> **sealed class**

`改写:`

sealed class Result
    class Success(val msg: String) : Result()
    class Failure(val error: Exception) : Result()
    
    fun getResultMsg(result: Result) = when (result) {
        is Success -> result.msg
        is Failure -> result.error.message
    }

<table> 
 <thead> 
  <tr> 
   <th>序号</th> 
   <th>Tips</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>1</td> 
   <td>密封类从编译器的角度保证了不会出现漏写条件的出现</td> 
  </tr> 
  <tr> 
   <td>2</td> 
   <td>密封类及其所有子类只能定义再=在同一个文件的顶层位置,不能嵌套咋其他类中</td> 
  </tr> 
 </tbody> 
</table>