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# 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.*;
    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 following result:

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

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