Java中的关联数组？

Question

I want add duplicate keys in map,output like the one below:

google:Android,google:Maps,apple:iPod,apple:iPhone,apple:iOS

Is it possible in java or json? please help me.

Answer 1

Yes, it is possible in Java. Check apache's MultiMap.

Answer 2

I like the MultiMap answer above. But if you want to stick to the java.util collections, try a map of lists.

Answer 3

Even better than a map of lists is a map of sets, assuming you only want to allow duplicate keys and not duplicate associations . It could be done like this:

import java.util.*;
Map<K, Set<V>> yourMap = new HashMap<K, Set<V>>();

public void add(K key, V value) {
    if (!yourMap.containsKey(key)) {
        yourMap.put(key, new HashSet<V>());
    }
    yourMap.get(key).add(value);
}

Replace K and V with the actual key and value types.

Answer 4

Map in java can never has duplicate key, however you can put multiple values for a particular key:

Map<String, List<String>> map = new HashMap<String, List<String>>();

You can also use MultivaluedMap .

Answer 5

Another good solution apart from Apache's library is to use Google's guava libraries. Guava implements a Multimap , and here's a blog post that explains how to use Guava's Multimaps