Java map and map.entry details and uses

The map is an interface in Java, and Map.entry is an internal interface to the map.

Map provides a number of common methods, such as keyset (), EntrySet (), and so on.

The return value of the KeySet () method is a collection of key values in map, and the return value of EntrySet () returns a set collection of type Map.entry.

Map.entry is an internal interface to the map declaration, which is generic and defined as entry<k,v>. It represents an entity (a Key-value pair) in a map. The interface has a getkey (), GetValue method.

From the above can be drawn, the common method of traversing map:

1. Map map = new HashMap ();

Irerator iterator = Map.entryset (). iterator ();

while (Iterator.hasnext ()) {

Map.entry Entry = Iterator.next ();

Object key = Entry.getkey ();

//

}

2.Map Map = new HashMap ();

Set keyset= Map.keyset ();

Irerator iterator = Keyset.iterator;

while (Iterator.hasnext ()) {

Object key = Iterator.next ();

Object value = Map.get (key);

//

}

In addition, there is a traversal method, simply traversing the value values, map has a values method, which returns the collection collection of value. By traversing collection, you can also traverse value, such as

Map map = new HashMap ();

Collection C = map.values ();

Iterator Iterator = C.iterator ();

while (Iterator.hasnext ()) {

Object value = Iterator.next ();

}

Java map and map.entry details and uses