There are two variants of descending() in Java.util.TreeMap, both are discussed in this article.
1. descendingKeySet(): It returns a reverse order Navigable Set view of the keys contained in the map.
Syntax : public NavigableSet descendingKeySet() Parameters: NA Return Value: It returns a reverse order navigable set view of the keys in this map. Exception: NA
// Java code to demonstrate the working // descendingKeySet() import java.io.*;
import java.util.*;
public class descendingKeySet1 {
public static void main(String[] args)
{
// Declaring the tree map of Integer and String
TreeMap<Integer, String> treemap = new TreeMap<Integer, String>();
// assigning the values in the tree map
// using put()
treemap.put( 2 , "two" );
treemap.put( 0 , "zero" );
treemap.put( 3 , "three" );
treemap.put( 6 , "six" );
treemap.put( 9 , "nine" );
treemap.put( 7 , "seven" );
// putting values in navigable set
// use of descendingKeySet
NavigableSet set1 = treemap.descendingKeySet();
System.out.println( "Navigable set values are: " + set1);
}
} |
Output:
Navigable set values are: [9, 7, 6, 3, 2, 0]
2. descendingMap() : It returns a reverse order view of the mappings contained in the map.
Syntax : public NavigableMap descendingMap() Parameters: NA Return Value It returns a reverse order view of the map. Exception: NA
// Java code to demonstrate the working // of descendingMap() import java.io.*;
import java.util.*;
public class descendingMap {
public static void main(String[] args)
{
// Declaring the tree map of Integer and String
TreeMap<Integer, String> treemap = new TreeMap<Integer, String>();
// assigning the values in the tree map
// using put()
treemap.put( 2 , "two" );
treemap.put( 0 , "zero" );
treemap.put( 3 , "three" );
treemap.put( 6 , "six" );
treemap.put( 9 , "nine" );
treemap.put( 7 , "seven" );
// putting values in navigable map
// use of descendingMap()
NavigableMap map1 = treemap.descendingMap();
System.out.println( "Navigable map values are: " + map1);
}
} |
Output:
Navigable map values are: {9=nine, 7=seven, 6=six, 3=three, 2=two, 0=zero}
Practical Application : There are many applications possible of descending functions explained in this article. Some among them are priority scheduling, or designing a ranking system. Latter one is demonstrated in the code below.
// Java code to demonstrate the application // of descendingMap() and descendingKetSet() import java.io.*;
import java.util.*;
public class descendingAppli {
public static void main(String[] args)
{
// Declaring the tree map of Integer and String
// to store participants info of scores with name
TreeMap<Integer, String> participants = new TreeMap<Integer, String>();
// assigning score of participants
// using put()
participants.put( 30 , "Ashty" );
participants.put( 45 , "Shavi" );
participants.put( 16 , "Vaish" );
participants.put( 15 , "Kil" );
participants.put( 11 , "Manju" );
// putting ranks in NavigableMap
// use of descendingMap() to assign 1st to
// maximum values and so on
NavigableMap<Integer, String> Ranks = participants.descendingMap();
System.out.println( "The ranks according to scores are : " );
// Printing values rankwise
int count = 0 ;
for (NavigableMap.Entry<Integer, String> entry : Ranks.entrySet()) {
count++;
String str = Integer.toString(count);
System.out.println( "Rank " + str + ": " + entry.getValue());
}
}
} |
Output:
The ranks according to scores are : Rank 1: Shavi Rank 2: Ashty Rank 3: Vaish Rank 4: Kil Rank 5: Manju
Article Tags :