null检查hashmap密钥 [英] null check for hashmap key

问题描述

我有一个场景，我需要检查 null 。我有一个名为 dT 的键：
$ b $ pre $ String dT =（String） caseChk.get（ DT）;


这会抛出 NullPointerException ，因为该键本身并不存在。如果我检查

  if（caseChk.get（dT）！= null）{
 // do 
 
  

另一个 NullPointerException 因为 .get 而被抛出。当地图中的某个键不存在时，如何测试 null ？我知道放置方法应该可以处理它，但这不在我的控制之下。]

解决

$ b

如果 $ b code> caseChk.get（dT）只是你有的那一行，并且确定它引发异常，那么只有可能性是 caseChk 可能为空。

I have a scenario where I need to check for null. I have a key named dT:

String dT = (String) caseChk.get("dT");

This throws a NullPointerException, since that key itself doesn't exist. If I check with

if(caseChk.get("dT") != null) {
    // do something
}

yet another NullPointerException is thrown because of .get. How can I test for null when a key in the map doesn't exist? I understand that the put method should handle it, but that isn't under my control.]

解决方案

Even now I get nullpoiner since .get throws exception

If caseChk.get("dT") is only line you have there and sure it is throwing exception, then only possibility is caseChk could be null.

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