Java 如果存在，如何更新地图中的值，否则将其插入
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How to update a value in a map if it exists else insert it
提问by Crazy Dino
I did a search and was amazed this hadn't been asked before (at least I couldn't find it).
我进行了搜索，很惊讶之前没有人问过这个问题（至少我找不到）。
I have a map like this:
我有一张这样的地图：
Map<String, String> myMap
I know that I can check if a key exists within the map usingcontainsKey(Object key);and I can replace a value using replace(String key, String value);and naturally put a value using put(String key, String value);
我知道我可以使用检查地图中是否存在一个键containsKey(Object key);，我可以使用替换值replace(String key, String value);并自然地使用put(String key, String value);
Now if I want to check a value if it exists update it, else insert it, I have to use a condition:
现在如果我想检查一个值是否存在更新它，否则插入它，我必须使用一个条件：
if(myMap.containsKey(key)) {
myMap.replace(key, value);
} else {
myMap.put(key, value);
}
Is there a better way of doing this? I personally feel the condition is a bit unnecessary and overcomplicating something which could be one line rather than five!
有没有更好的方法来做到这一点？我个人觉得这个条件有点不必要并且过于复杂，可能是一行而不是五行！
采纳答案by Jens
The replace will be done by put():
替换将通过put()：
From the documentation of HashMap
来自HashMap的文档
public V put(K key, V value) Associates the specified value with the specified key in this map. If the map previously contained a mapping for the key, the old value is replaced.
public V put(K key, V value) 将指定值与此映射中的指定键相关联。如果映射先前包含键的映射，则旧值将被替换。
So you only need
所以你只需要
myMap.put(key, value);
回答by Suresh Atta
Remove all the code and below line is enough.
删除所有代码，下面一行就足够了。
myMap.put(key, value);
That already checks and replaces if any value exist already.
如果已经存在任何值，它已经检查并替换。
回答by meskobalazs
You can just use the #put()method, it will replace the existing item if there is one. By the way AbstractMap(the superclass of HashMap) implements #replace()this way:
您可以只使用该#put()方法，如果有，它将替换现有项目。顺便说一下AbstractMap（的超类HashMap）是这样实现的#replace()：
default boolean replace(K key, V oldValue, V newValue) {
Object curValue = get(key);
if (!Objects.equals(curValue, oldValue) ||
(curValue == null && !containsKey(key))) {
return false;
}
put(key, newValue);
return true;
}
In your case, you don't need the extra checks of this method.
在您的情况下，您不需要此方法的额外检查。
