英文:
If hashmap only contains one key, is there a way to get that key without knowing anything about it?
问题
我有一个只有一个键（和一个值）的哈希表。假设我不知道那个键或键的值。有没有办法找到它？这可能听起来很愚蠢，但既然只有一个键，那么有没有办法获取那个键。
英文:
I have a hashamp with only one key (and a value). Lets say I don't know the key or value of that one key. Is there a way to find it? This may sound dumb but since there is only ONE key, then would there be a way to get that key.
答案1
得分: 1
对于单个键映射，只需执行以下操作：
Map<String, String> map = Map.of("A", "B");
System.out.println(map.keySet().iterator().next());
输出：
A
对于更多元素的映射，您可以执行以下操作：
您可以通过map.keySet()获取映射的keySet()并遍历它。
如果您想尝试找到与value关联的特定键，可以通过获取映射的entrySet()，然后执行以下操作：
String targetVal = "some value";
for (Entry<String, String> e : map.entrySet()) {
if (e.getValue().equals(targetVal)) {
System.out.println(e.getKey());
// 或者
System.out.println(e);
// 继续迭代，因为多个键可以映射到相同的值。
}
}
英文:
For a single key map just do the following:<br>
Map<String,String> map = Map.of("A","B");
System.out.println(map.keySet().iterator().next());
prints
A
For a more populated map you can do the following:
You can get the keySet() of the map via map.keySet() and iterate thru that.
If you want to try and find a particular key associated with a value you can
get the entrySet() of the map and do something like this:
String targetVal = "some value";
for (Entry<String,String> e : map.entrySet()) {
if (e.getValue().equals(targetVal)) {
System.out.println(e.getKey());
// or
System.out.println(e);
// keep iterating since multiple keys can
// map to the same value.
}
}
答案2
得分: 0
你可以使用 hash_map.keySet() 获取你所有的键。
链接：https://www.geeksforgeeks.org/hashmap-keyset-method-in-java/
英文:
You can get all of your keys with hash_map.keySet()
https://www.geeksforgeeks.org/hashmap-keyset-method-in-java/
答案3
得分: 0
是的，您可以使用iterator，它使您能够在任何Collection（或Map的entrySet()）上进行迭代：
public class Main {
public static void main(String[] args) {
Map<String, String> map = new HashMap<>();
map.put("First", "Entry");
System.out.println(map.entrySet().iterator().next());
}
}
这将打印出：First=Entry，其中First是键，Entry是值。
英文:
Yes, you can use iterators, which enable you to iterate over any Collection (or Map's entrySet()):
public class Main {
public static void main(String[] args) {
Map<String, String> map = new HashMap<>();
map.put("First", "Entry");
System.out.println(map.entrySet().iterator().next());
}
}
This prints: First=Entry, where First is the key and Entry is the value.
答案4
得分: 0
hashMapObj.entrySet().iterator().next();
是你问题的答案。
英文:
hashMapObj.entrySet().iterator().next();
is the answer to your question.
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