ConcurrentNavigableMap Interface in Java

The ConcurrentNavigableMap interface is a member of the Java Collection Framework. It extends from the NavigableMap interface and ConcurrentMap interface. The ConcurrentNavigableMap provides thread-safe access to map elements along with providing convenient navigation methods. It belongs to java.util.concurrent package.

Declaration:

public interface ConcurrentNavigableMap<K,V> extends ConcurrentMap<K,V>, NavigableMap<K,V>

Here, K is the key Object type and V is the value Object type.

The Hierarchy of ConcurrentNavigableMap

It implements ConcurrentMap<K,​ V>, Map<K, ​V>, NavigableMap<K,​ V>, SortedMap<K,​ V> interfaces. ConcurrentSkipListMap implements ConcurrentNavigableMap.

Example:

 
Output:

Mappings of ConcurrentNavigableMap : {1=First, 2=Second, 3=Third, 4=Fourth}
HeadMap(3): {1=First, 2=Second}
TailMap(3): {3=Third, 4=Fourth}
SubMap(1, 3): {1=First, 2=Second}

Implementing Classes

The ConcurrentNavigableMap has one implementing class which is ConcurrentSkipListMap class. The ConcurrentSkipListMap is a scalable implementation of the ConcurrentNavigableMap interface. The keys in ConcurrentSkipListMap are sorted by natural order or by using a Comparator at the time of construction of the object. The ConcurrentSkipListMap has the expected time cost of log(n) for insertion, deletion, and searching operations. It is a thread-safe class, therefore, all basic operations can be accomplished concurrently.
 
Syntax:

ConcurrentSkipListMap< ? , ? > objectName = new ConcurrentSkipListMap< ? , ? >();

Example: In the code given below, we simply instantiate an object of the ConcurrentSkipListMap class named cslmap. The put() method is used to add elements and remove() to delete elements. For the remove() method the syntax is objectname.remove(Object key). The keySet() shows all the keys in the map (description in the method table given above).

Output:

The ConcurrentSkipListMap contains: {1=Geeks, 2=For, 3=Geeks}

The ConcurrentSkipListMap key set: [1, 2, 3]

The ConcurrentSkipListMap contains: {1=Geeks, 2=For}

Basic Operations on ConcurrentNavigableMap

1. Adding Elements

To add elements to a ConcurrentNavigableMap we can use any methods of the Map interface. The code below shows how to use them. You can observe in the code that when no Comparator is provided at the time of construction, the natural order is followed.

 
Output:

Mappings of ConcurrentNavigableMap : {3=First, 6=Second, 8=Third}

2. Removing Elements

To remove elements as well we use methods of the Map interface, as ConcurrentNavigableMap is a descendant of Map.

 
Output:

Mappings of ConcurrentNavigableMap : {3=First, 6=Second, 8=Third, 11=Fourth}

ConcurrentNavigableMap, after remove operation : {3=First, 11=Fourth}

ConcurrentNavigableMap, after clear operation : {}

3. Accessing the Elements

We can access the elements of a ConcurrentNavigableMap using get() method, the example of this is given below.

 
Output:

First
Second
Third
Fourth

The ConcurrentNavigableMap key set: [3, 6, 8, 11]

4. Traversing

We can use the Iterator interface to traverse over any structure of the Collection Framework. Since Iterators work with one type of data we use .Entry< ? , ? > to resolve the two separate types into a compatible format. Then using the next() method we print the elements of the ConcurrentNavigableMap.

 
Output:

Key = 3, Value = First
Key = 6, Value = Second
Key = 8, Value = Third
Key = 11, Value = Fourth

Note: Every time that we say ‘elements of ConcurrentNavigableMap’, it has to be noted that the elements are actually stored in the object of an implementing class of ConcurrentNavigableMap in this case ConcurrentSkipListMap.

Methods of ConcurrentNavigableMap

ConcurrentNavigableMap inherits methods from the Map interface, SortedMap interface, ConcurrentMap interface, NavigableMap interface. The basic methods for adding elements, removing elements, and traversal are given by the parent interfaces. The methods of the ConcurrentNavigableMap are given in the following table. Here,

• K – The type of the keys in the map.
• V – The type of values mapped in the map.

Methods declared in interface java.util.concurrent.ConcurrentMap

Methods declared in interface java.util.Map

Methods declared in interface java.util.NavigableMap

Methods declared in interface java.util.SortedMap