英文:
Determine if 'put' operation actually executed in putIfAbsent method of ConcurrentHashMap?
问题
我想知道ConcurrentHashMap的putIfAbsent方法中是否实际执行了'put'操作。
这是我想要的：
if(map.putIfAbsent(Key,Value)){//显然这是错误的return true;}//其他操作return false;
英文:
I want to know whether 'put' operation actually executed in putIfAbsent method of ConcurrentHashMap.
This is what I want:
if(map.putIfAbsent(Key,Value)){//Clearly this is wrongreturn true;}//other operationreturn false;
答案1
得分: 5
Map#putIfAbsent 如果没有关联的键存在或键的值为null，则会返回null。否则，它将返回现有的值。
V resultOfPut = map.putIfAbsent(key, value);if (resultOfPut == null) {// 能够放置} else {// 无法放置，值已存在}
英文:
Map#putIfAbsent will return null if no associated key exists or the value for the key is null. Otherwise it will return the existing value.
V resultOfPut = map.putIfAbsent(key, value);if (resultOfPut == null) {// was able to put} else {// was not able to put, value already exists}
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