groovy：在地图上找到一个键并返回其值 [英] groovy: find a key in a map and return its value

问题描述

我想在给定的地图中找到一个特定的键。如果找到密钥，我想从地图中获取该密钥的值。

这是我到目前为止管理的：

  def mymap = [name：Gromit，喜欢：cheese，id：1234] 
 
 def x = mymap。找到{it.key ==喜欢} 
 
如果（x）
 println x.value 
  

这样做，输出是预期的奶酪。太好了，但我不想在最后做 x.value ，而且我不想做 if（x）。我想要x直接包含值。

我不能直接得到这个值，就像这样：

def mymap = [name：Gromit，喜欢：cheese，id：1234]

def x = mymap.find {it.key ==likesZZZ} .value

println x

因为找到在这种情况下，闭包为空，这将导致空指针异常。当然，当 it.key ==喜欢时，上述代码片段可以正常工作，但我不确定我会始终在地图中找到目标键。 p>

什么是Groovier和安全的方法来做到这一点：

• 检查地图是否具有给定的键，如果是，则获取该键的值

解决方案

  def mymap = [name：Gromit，id：1234] 
 def x = mymap.find {it。 key ==likes}？value 
 if（x）
 printlnx value：$ {x}
 
 println x.getClass（）。name 
  

？。检查null，不创建Groovy中例外。如果密钥不存在，结果将是一个 org.codehaus.groovy.runtime.NullObject 。

I want to find a specific key in a given map. If the key is found, I then want to get the value of that key from the map.

This is what I managed so far:

def mymap = [name:"Gromit", likes:"cheese", id:1234]

def x = mymap.find{ it.key == "likes" }

if(x)
    println x.value

This works, the output is "cheese" as expected. Great, but I don't want to do x.value at the end, and I don't want to do if(x). I want x to directly contain the value somehow.

I can't get the value directly into x like this:

def mymap = [name:"Gromit", likes:"cheese", id:1234]

def x = mymap.find{ it.key == "likesZZZ" }.value

println x

Because the find closure is null in this case, this results in a Null Pointer Exception. Of course, the above code snippet works when it.key == "likes", but I am not sure that I will always find the target key in the map.

What is a "Groovier" and safe way to do this on a map:

• Check if a map has a given key,
• And if so, get the value of this key

解决方案

def mymap = [name:"Gromit", id:1234]
def x = mymap.find{ it.key == "likes" }?.value
if(x)
    println "x value: ${x}"

println x.getClass().name

?. checks for null and does not create an exception in Groovy. If the key does not exist, the result will be a org.codehaus.groovy.runtime.NullObject.

这篇关于groovy：在地图上找到一个键并返回其值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！