Java - The SortedMap Interface

The SortedMap interface extends Map. It ensures that the entries are maintained in 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.

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

SN	Methods with Description
1	Comparator comparator( ) Returns the invoking sorted map's comparator. If the natural ordering is used for the invoking map, null is returned.
2	Object firstKey( ) Returns the first key in the invoking map.
3	SortedMap headMap(Object end) Returns a sorted map for those map entries with keys that are less than end.
4	Object lastKey( ) Returns the last key in the invoking map.
5	SortedMap subMap(Object start, Object end) Returns a map containing those entries with keys that are greater than or equal to start and less than end
6	SortedMap tailMap(Object start) Returns a map containing those entries with keys that are greater than or equal to start.

Example:

SortedMap have its implementation in various classes like TreeMap, Following is the example to explain SortedMap functionlaity:

import java.util.*;

public class TreeMapDemo {

public static void main(String args[]) {
// Create a hash map
TreeMap tm = new TreeMap();
// Put elements to the map
tm.put("Zara", new Double(3434.34));
tm.put("Mahnaz", new Double(123.22));
tm.put("Ayan", new Double(1378.00));
tm.put("Daisy", new Double(99.22));
tm.put("Qadir", new Double(-19.08));

// Get a set of the entries
Set set = tm.entrySet();
// Get an iterator
Iterator i = set.iterator();
// Display elements
while(i.hasNext()) {
Map.Entry me = (Map.Entry)i.next();
System.out.print(me.getKey() + ": ");
System.out.println(me.getValue());
}
System.out.println();
// Deposit 1000 into Zara's account
double balance = ((Double)tm.get("Zara")).doubleValue();
tm.put("Zara", new Double(balance + 1000));
System.out.println("Zara's new balance: " +
tm.get("Zara"));
}
}

This would produce the following result:

Ayan: 1378.0
Daisy 99.22
Mahnaz: 123.22
Qadir: -19.08
Zara: 3434.34
Zara.s current balance: 4434.34