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Java Hashmap: How to get key from value?
Bi-directional Map in Java?
I want a key value data structure to use for Android App. I can use Map<K,V>, but in Map I can't get key for particular Value.
Is there any good Java data structure using which I can retrieve key by value and vice-versa.
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One of these data structures is called Multimap and it allows us to store duplicate keys in a more elegant fashion.
For just storing simple values, you should use an implementation of the List<E> interface. Depending on your use either an ArrayList<E> or LinkedList<E> will do what you need. Another option would be a Map<K, V> (it's implementation HashMap ). This will allow you to save duplicate values under unique keys.
You can use Multimap it supports duplicate keys but it also support duplicate keys and value pairs. Best solution for you is use Multimap and check if value already exist then dont add it.
key-value store, or key-value database is a simple database that uses an associative array (think of a map or dictionary) as the fundamental data model where each key is associated with one and only one value in a collection. This relationship is referred to as a key-value pair.
You can use Map with entrySet and Map.Entry class to iterate and get both keys and values even if you don't know any of the keys in the Map.
Map <Integer,String> myMap = new HashMap<Integer,String>();
Iterator<Entry<Integer, String>> iterator = myMap.entrySet().iterator();
while (iterator.hasNext()) {
Map.Entry<Integer,String> pairs = (Map.Entry<Integer,String>)iterator.next();
String value = pairs.getValue();
Integer key = pairs.getKey();
System.out.println(key +"--->"+value);
}
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