Guava Pack Learning---Bimap

Bimap is also the new collection class provided in guava, the alias is called Two-way map, is key-"value,value-" key, that is, you can locate the value by key, you can also use value to locate key.

This scenario is often encountered in everyday development.

In fact, Bimap is relatively simple, it is an interface, extension of the map interface, which is also the <K,V> format, but it is not allowed to have a duplicate V, This is important, when you try to put a duplicate V is an error message prompt. A V without a repeat will ensure that when you turn the map upside down, the K can be uniquely positioned, and we can look at its implementation:

Old habits, or see hashbimap, the creation of the new collection class is basically using the Create method:

 Public static <k, v> hashbimap<k, v> Create () {    return Create (+);  }   publicstatic <k, v> hashbimap<k, v> create (int  expectedsize) {     return New Hashbimap<k, v>(expectedsize);  }

Its additions and deletions are basically no different from the normal map, except that the same value can not be inserted into.

The point is that it has a reverse function:

@Override PublicBimap<v, k>inverse () {return(Inverse = =NULL) ? Inverse =Newinverse (): inverse; }  Private Final classInverseextendsAbstractmap<v, k>ImplementsBimap<v, k>, Serializable {BiMap<k, v>forward () {returnHashbimap. This; } @Override Public intsize () {returnsize; } @Override Public voidClear () {forward (). Clear (); } @Override Public BooleanContainsKey (@Nullable Object value) {returnforward (). Containsvalue (value); } @Override PublicK Get (@Nullable Object value) {returnmaps.keyornull (Seekbyvalue (Value, Smearedhash (value))); } @Override PublicK put (@Nullable V value, @Nullable k key) {returnPutinverse (value, key,false); } @Override Publick forceput (@Nullable V value, @Nullable k key) {returnPutinverse (value, key,true); } @Override PublicK Remove (@Nullable Object value) {Bientry<k, v> entry =Seekbyvalue (value, Smearedhash (value)); if(Entry = =NULL) {        return NULL; } Else{Delete (entry); Entry.previnkeyinsertionorder=NULL; Entry.nextinkeyinsertionorder=NULL; returnEntry.key; }    }

In fact, the <K,V> into a <v,k>, and this reverse is in the back you re-modify the map, it will also follow the change, so do not worry about it is a one-time, otherwise it is better to iterate to get a new map out:

 Public void Testbimap () {        hashbimap<String,String> map = hashbimap.create ();        Map.put ("1", "2");        Map.put ("3", "4");        System.out.println (Map.tostring ());        System.out.println (Map.inverse (). toString ());        Map.put ("5", "6");        System.out.println (Map.inverse (). toString ());    }

{1=2, 3=4}
{2=1, 4=3}
{2=1, 4=3, 6=5}

To this end, take a look at the last Guava Collection Class table.

Guava Pack Learning---Bimap