如何检查一个元素是否已从 Map 中删除

Question

How can I check that an element has been properly removed from a Map in java?

Given:

ConcurrentHashMap<Integer,Object> myMap = new ConcurrentHashMap<>();
myMap.put(1, new Object());

myMap.remove(1);

Is the below code the only way to check it?

myMap.contains(1);

Answer 1

remove() returns the removed object, or null if it is not present in the map:

Returns:
the previous value associated with key, or null if there was no mapping for key.

Object removedObject = myMap.remove(1);
boolean wasRemoved = removedObject != null;

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In fact by using, contains() , the object might have been removed by another thread between the calls to remove() and contains() , if the map is shared between threads. That your question uses a ConcurrentHashMap hints that concurrency might be a case here.