Java SortedMap Interface

In diesem Tutorial werden wir das Java SortedMap-Interface und seine Methoden lernen.

Das SortedMap-Interface der Java-Kollektionsrahmen kann die in der Abbildung gespeicherten Schlüssel sortieren.

It inheritsMap interface.

Classes that implement SortedMap

Because SortedMap is an interface, we cannot create an object from it.

To use the features of the SortedMap interface, we need to use the class TreeMap that implements it.

How to use SortedMap?

To use SortedMap, we must first import the java.util.SortedMap package. After importing the package, you can create a sorted map as follows.

//　The SortedMap implementation is provided by the TreeMap class
SortedMap<Key, Value> numbers = new TreeMap<>();

We have created a named numbers sorted mapping using the TreeMap class.

Here,

• Key - Used as a unique identifier to associate each element (value) in the mapping

• Value - The elements associated with the key in the map

Here, we have not used any parameters to create a sorted mapping. Therefore, the mapping will be naturally sorted (ascending).

Methods of SortedMap

The SortedMap interface includes all the methods of the Map interface. This is because Map is the superinterface of SortedMap.

In addition to all these methods, there are also methods specific to the SortedMap interface.

• comparator() - Returns a comparator that can be used to sort the keys in the mapping

• firstKey() - Returns the first key of the sorted mapping

• lastKey() - Returns the last key of the sorted mapping

• headMap(key) - Returns all entries of the mapping whose keys are less than the specified key key

• tailMap(key) - Returns all entries of the mapping whose keys are greater than or equal to the specified key key

• subMap(key1,key2) -Returns the key located at key1and key2between (including key1All entries of the mapping

Implementation of SortedMap in TreeMap class

import java.util.SortedMap;
import java.util.TreeMap;
class Main {
　　　　public static void main(String[] args) {
　　　　　　　　//Using TreeMap to create SortedMap
　　　　　　　　SortedMap<String, Integer> numbers = new TreeMap<>();
　　　　　　　　//Insert mapping element
　　　　　　　　numbers.put("Two",　2);
　　　　　　　　numbers.put("One",　1);
　　　　　　　　System.out.println("SortedMap:  ",　+　numbers);
　　　　　　　　//Access the first key of the map
　　　　　　　　System.out.println("First key:  ",　+　numbers.firstKey());
　　　　　　　　//Access the last key of the map
　　　　　　　　System.out.println("Last key:  ",　+　numbers.lastKey());
　　　　　　　　//Remove elements from the map
　　　　　　　　int  value  =  numbers.remove("One");
　　　　　　　　System.out.println("Delete value:  ",　+　value);
　　　　}
}

Output result

SortedMap:  {One=1,  Two=2}
First key:  One
Last key:  Two
Delete value:　1

For more information on TreeMap, please visitJava TreeMap.

Since we understand the SortedMap interface, we will use the TreeMap class to learn its implementation.