Multimap interface extends Map so that its keys can be mapped to multiple values at a time.
Interface Declaration
Following is the declaration for com.google.common.collect.Multimap<K,V> interface −
@GwtCompatible public interface Multimap<K,V>
Interface Methods
| Sr.No | Method & Description |
|---|---|
| 1 | Map<K,Collection<V>> asMap()Returns a view of this multimap as a Map from each distinct key to the nonempty collection of that key’s associated values. |
| 2 | void clear()Removes all key-value pairs from the multimap, leaving it empty. |
| 3 | boolean containsEntry(Object key, Object value)Returns true if this multimap contains at least one key-value pair with the key and the value. |
| 4 | boolean containsKey(Object key)Returns true if this multimap contains at least one key-value pair with the key. |
| 5 | boolean containsValue(Object value)Returns true if this multimap contains at least one key-value pair with the value. |
| 6 | Collection<Map.Entry<K,V>> entries()Returns a view collection of all key-value pairs contained in this multimap, as Map.Entry instances. |
| 7 | boolean equals(Object obj)Compares the specified object with this multimap for equality. |
| 8 | Collection<V> get(K key)Returns a view collection of the values associated with key in this multimap, if any. |
| 9 | int hashCode()Returns the hash code for this multimap. |
| 10 | boolean isEmpty()Returns true if this multimap contains no key-value pairs. |
| 11 | Multiset<K> keys()Returns a view collection containing the key from each key-value pair in this multimap, without collapsing duplicates. |
| 12 | Set<K> keySet()Returns a view collection of all distinct keys contained in this multimap. |
| 13 | boolean put(K key, V value)Stores a key-value pair in this multimap. |
| 14 | boolean putAll(K key, Iterable<? extends V> values)Stores a key-value pair in this multimap for each of values, all using the same key, key. |
| 15 | boolean putAll(Multimap<? extends K,? extends V> multimap)Stores all key-value pairs of multimap in this multimap, in the order returned by multimap.entries(). |
| 16 | boolean remove(Object key, Object value)Removes a single key-value pair with the key and the value from this multimap, if such exists. |
| 17 | Collection<V> removeAll(Object key)Removes all values associated with the key. |
| 18 | Collection<V> replaceValues(K key, Iterable<? extends V> values)Stores a collection of values with the same key, replacing any existing values for that key. |
| 19 | int size()Returns the number of key-value pairs in this multimap. |
| 20 | Collection<V> values()Returns a view collection containing the value from each key-value pair contained in this multimap, without collapsing duplicates (so values().size() == size()). |
Example of Multimap
Create the following java program using any editor of your choice in say C:/> Guava.
GuavaTester.java
import java.util.Collection;
import java.util.List;
import java.util.Map;
import java.util.Set;
import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.Multimap;
public class GuavaTester {
public static void main(String args[]) {
GuavaTester tester = new GuavaTester();
Multimap<String,String> multimap = tester.getMultimap();
List<String> lowerList = (List<String>)multimap.get("lower");
System.out.println("Initial lower case list");
System.out.println(lowerList.toString());
lowerList.add("f");
System.out.println("Modified lower case list");
System.out.println(lowerList.toString());
List<String> upperList = (List<String>)multimap.get("upper");
System.out.println("Initial upper case list");
System.out.println(upperList.toString());
upperList.remove("D");
System.out.println("Modified upper case list");
System.out.println(upperList.toString());
Map<String, Collection<String>> map = multimap.asMap();
System.out.println("Multimap as a map");
for (Map.Entry<String, Collection<String>> entry : map.entrySet()) {
String key = entry.getKey();
Collection<String> value = multimap.get("lower");
System.out.println(key + ":" + value);
}
System.out.println("Keys of Multimap");
Set<String> keys = multimap.keySet();
for(String key:keys) {
System.out.println(key);
}
System.out.println("Values of Multimap");
Collection<String> values = multimap.values();
System.out.println(values);
}
private Multimap<String,String> getMultimap() {
//Map<String, List<String>>
// lower -> a, b, c, d, e
// upper -> A, B, C, D
Multimap<String,String> multimap = ArrayListMultimap.create();
multimap.put("lower", "a");
multimap.put("lower", "b");
multimap.put("lower", "c");
multimap.put("lower", "d");
multimap.put("lower", "e");
multimap.put("upper", "A");
multimap.put("upper", "B");
multimap.put("upper", "C");
multimap.put("upper", "D");
return multimap;
}
}
Verify the Result
Compile the class using javac compiler as follows −
C:\Guava>javac GuavaTester.java
Now run the GuavaTester to see the result.
C:\Guava>java GuavaTester
See the result. Initial lower case list [a, b, c, d, e] Modified lower case list [a, b, c, d, e, f] Initial upper case list [A, B, C, D] Modified upper case list [A, B, C] Multimap as a map upper:[a, b, c, d, e, f] lower:[a, b, c, d, e, f] Keys of Multimap upper lower Values of Multimap [a, b, c, d, e, f, A, B, C]
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