从Singleton Map从值获取密钥-Java

Question

I am looking to retrieve key from the value for a SingletonMap

Map<String,String> map = Collections.singletonMap("key1", "value1");

I am looking for a easy way to get the key, based on value. Rather then way that I have done before. Which I feel is too much overhead for a singleTon Map.

public static List<String> getKey(String value, Map<String, String> map) 
{
    List<String> keys = new ArrayList<String>();
    for(Entry<String, String> entry:map.entrySet()) 
    {
        if(value.equals(entry.getValue())) 
        {
            keys.add(entry.getKey());
        }
    }
    return keys;
}

Any inputs or suggestion will be helpful.

Answer 1

A singleton map has exactly one entry in it, so you can just do this:

    Map<String,String> map = Collections.singletonMap("key1", "value1");

    String theOnlyKeyInTheMap = map.keySet().iterator().next();

Answer 2

I am not sure why do you want this, however I do not think that is possible in any other way. You may be able to make the code readable using something like the Guava Maps.transformEntries call, supplied with a proper transformer function.