Java - SortedMap Interface

The SortedMap interface extends Map. It ensures that the entries are maintained in an ascending key order.

Several methods throw a NoSuchElementException when no items are in the invoking map. A ClassCastException is thrown when an object is incompatible with the elements in a map. A NullPointerException is thrown if an attempt is made to use a null object when null is not allowed in the map.

SortedMap Interface Methods

The methods declared by SortedMap are summarized in the following table −

Hierarchy of SortedMap Interface

The following diagram shows the hierarchy of SortedMap Interface in Java -

Operations on SortedMap Interface

Creating a SortedMap

TreeMap class implements the SortedMap interface. We can use the TreeMap constructor to create a SortedMap instance.

Syntax

Following is the syntax to create a sortemap instance:

 // Create a sorted map SortedMap<String, Double> map = new TreeMap<>(); 

Here we're creating a sorted map of String vs Double values. This map will store the keys based on alphanumeric order.

Adding Value to a SortedMap

SortedMap provides the put() method, which can be used to add value to a sortedmap instance. Whenever a value is added to the map, the map automatically sorts itself based on the keys entered.

Syntax

 public V put(K key,V value) 

Where the Key-Value pair represents the key and value associated with each other and are stored in the map. If this key is already associated with a value then that value is returned and the new value is associated with the key otherwise a null value is returned.

Example

 // Put elements to the map map.put("Zara", Double.valueOf(3434.34)); map.put("Mahnaz", Double.valueOf(123.22)); map.put("Ayan", Double.valueOf(1378.00)); map.put("Daisy", Double.valueOf(99.22)); map.put("Qadir", Double.valueOf(-19.08)); 

Getting value from a SortedMap

Using the get(key) method, we can retrieve the value associated with a key.

Syntax

 public V get(Object key) 

If the key is not present in the map, then it will return null otherwise it will return the associated value with the key provided.

Example

 Double value = map.get("Qadir"); System.out.print("Qadir: " + value); 

Updating value of a SortedMap

We can update an existing value of a sortedmap by calling the put() method again with the same key. Being a sortedmap, the entries will be sorted again based on the sorting order of the newly entered key(s).

Example

 // Put elements to the map map.put("Zara", Double.valueOf(3434.34)); map.put("Mahnaz", Double.valueOf(123.22)); map.put("Zara", Double.valueOf(1378.00)); 

SortedMap will consider the latest put() method call to update the entry with same key.

Deleting a value from a sortedmap

Using remove(key) method, we can remove the key, value associated with a key.

Syntax

 public V remove(Object key) 

If key is not present in the map, then it will return null otherwise it will remove key-value association from the map and sort the map accordingly.

Example

 Double value = map.remove("Qadir"); System.out.print("Qadir removed with value: " + value); 

Iterating sortedMap

SortedMap entries can be easily navigated. SortedMap provided a method entrySet() which provides all the entries in form of set.

Syntax

 public Set<Map.Entry<K,V>> entrySet() 

Where Map.Entry contains the key-value pair to be iterated.

Example

 // Get a set of the entries Set<Map.Entry<String, Double>> set = map.entrySet(); // Get an iterator Iterator<Map.Entry<String, Double>> i = set.iterator(); // Display elements while(i.hasNext()) { Map.Entry<String, Double> me = i.next(); System.out.println(me.getKey()); } 

Examples of SortedMap Interface

Example 1

Following is an example showing how TreeMap can be used to get values of a SortedMap −

 import java.util.Iterator; import java.util.Map; import java.util.Set; import java.util.SortedMap; import java.util.TreeMap; public class MapDemo { public static void main(String args[]) { // Create a hash map SortedMap<String, Double> map = new TreeMap<>(); // Put elements to the map map.put("Zara", Double.valueOf(3434.34)); map.put("Mahnaz", Double.valueOf(123.22)); map.put("Ayan", Double.valueOf(1378.00)); map.put("Daisy", Double.valueOf(99.22)); map.put("Qadir", Double.valueOf(-19.08)); // Get a set of the entries Set<Map.Entry<String, Double>> set = map.entrySet(); // Get an iterator Iterator<Map.Entry<String, Double>> i = set.iterator(); // Display elements while(i.hasNext()) { Map.Entry<String, Double> me = i.next(); System.out.print(me.getKey() + ": "); System.out.println(me.getValue()); } } } 

Output

 Ayan: 1378.0 Daisy: 99.22 Mahnaz: 123.22 Qadir: -19.08 Zara: 3434.34 

Example 2

Following is an example showing how TreeMap can be used to set values of a SortedMap −

 import java.util.Iterator; import java.util.Map; import java.util.Set; import java.util.SortedMap; import java.util.TreeMap; public class MapDemo { public static void main(String args[]) { // Create a hash map SortedMap<String, Double> map = new TreeMap<>(); // Put elements to the map map.put("Zara", Double.valueOf(3434.34)); map.put("Mahnaz", Double.valueOf(123.22)); map.put("Ayan", Double.valueOf(1378.00)); map.put("Daisy", Double.valueOf(99.22)); map.put("Qadir", Double.valueOf(-19.08)); // Get a set of the entries Set<Map.Entry<String, Double>> set = map.entrySet(); // Get an iterator Iterator<Map.Entry<String, Double>> i = set.iterator(); // Display elements while(i.hasNext()) { Map.Entry<String, Double> me = i.next(); me.setValue(me.getValue() * 10); System.out.print(me.getKey() + ": "); System.out.println(me.getValue()); } } } 

Output

 Ayan: 13780.0 Daisy: 992.2 Mahnaz: 1232.2 Qadir: -190.79999999999998 Zara: 34343.4 

Example 3

Following is an example showing how a TreeMap can be used to get key of a sortedMap entry −

 import java.util.Iterator; import java.util.Map; import java.util.Set; import java.util.SortedMap; import java.util.TreeMap; public class MapDemo { public static void main(String args[]) { // Create a hash map SortedMap<String, Double> map = new TreeMap<>(); // Put elements to the map map.put("Zara", Double.valueOf(3434.34)); map.put("Mahnaz", Double.valueOf(123.22)); map.put("Ayan", Double.valueOf(1378.00)); map.put("Daisy", Double.valueOf(99.22)); map.put("Qadir", Double.valueOf(-19.08)); // Get a set of the entries Set<Map.Entry<String, Double>> set = map.entrySet(); // Get an iterator Iterator<Map.Entry<String, Double>> i = set.iterator(); // Display elements while(i.hasNext()) { Map.Entry<String, Double> me = i.next(); System.out.println(me.getKey()); } } } 

Output

 Ayan Daisy Mahnaz Qadir Zara 

Advantages of SortedMap Interface

• SortedMap ensures that the map is always sorted in ascending order of the keys. Whenever a key-value pair is added to the sortedmap, it is re-sorted
• Being sorted, sortedmap is very efficient in searches. In the case of large read-only datasets, sortedmap is an ideal choice to be implemented.
• We can customize the sorting mechanism by using a comparator on the key type.

Disadvantages of SortedMap Interface

• As a sortedmap has to be sorted every time an entry is added or changed, it becomes a performance bottleneck where changes are very frequent. In such cases, sortedmap is not preferred.
• As sortedMap maintains sort ability based on key, a key should be comparable and thus we cannot use a custom key if it is not implementing the comparable interface.