SortedMap Interface in JAVA

The Collection Framework provides a special Map interface for maintaining elements in a sorted order called SortedMap.A SortedMap is a Map that maintains its entries in ascending order, sorted according to the keys' natural ordering, or according to a Comparator provided at the time of the SortedMap creation. The SortedMap interface extends Map. It ensures that the entries are maintained in ascending key order.

NOTE: SortedMap 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.

Following is the SortedMap interface.

public interface SortedMap<K, V> extends Map<K, V>{
    Comparator<? super K> comparator();
    SortedMap<K, V> subMap(K fromKey, K toKey);
    SortedMap<K, V> headMap(K toKey);
    SortedMap<K, V> tailMap(K fromKey);
    K firstKey();
    K lastKey();
}

Following table shows the list of methods available in Map interface:

Example:

package com.sample.javase.testing;

import java.util.Iterator;

import java.util.Map;

import java.util.Map.Entry;

import java.util.Set;

import java.util.SortedMap;

import java.util.TreeMap;

public class SortedMapInterfaceExample {

/**

* @param args

*/

public static void main(String[] args) {

SortedMap<String, String> sortedMap = new TreeMap<String, String>();

sortedMap.put("oop1", "java");

sortedMap.put("oop2", "c++");

sortedMap.put("oop3", "objective-c");

System.out.println(sortedMap);// it maintains ascending order.

System.out.println("first key is" + sortedMap.firstKey());

System.out.println("Last key is " + sortedMap.lastKey());

/**

* Following lines of code specifies hoe to get the map values form

* iterator. For this first we need to get entry set or key set from

* map.Here we are using entryset() method.

*/

Set set = sortedMap.entrySet();

for (Iterator iterator = set.iterator(); iterator.hasNext();) {

Map.Entry entry = (Entry) iterator.next();

System.out.println("key is " + entry.getKey());

System.out.println("value is " + entry.getValue());

}

/**

* Following lines of code specifies hoe to get the map values form

* iterator. For this first we need to get entry set or key set from

* map.Here we are using keyset() method.

*/

Set set2 = sortedMap.keySet();

for (Iterator iterator = set2.iterator(); iterator.hasNext();) {

Object object = (Object) iterator.next();

System.out.println("key is " + object + "value is " + sortedMap.get(object));

}

}

}