哈希映射键的空检查 [英] null check for hashmap key

问题描述

我有一个需要检查 null 的场景.我有一个名为 dT 的密钥:

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

这会抛出一个 NullPointerException，因为该键本身不存在.如果我检查

if(caseChk.get("dT") != null) {//做一点事}

又一个 NullPointerException 由于 .get 被抛出.当映射中的键不存在时，如何测试 null ?我知道 put 方法应该处理它，但这不在我的控制之下.]

解决方案

即使现在我得到 nullpoiner 因为 .get 抛出异常

如果 caseChk.get("dT") 只是你在那里的行并且确定它正在抛出异常，那么唯一的可能性是 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.

这篇关于哈希映射键的空检查的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！