Java.util.TreeMap.descendingMap() and descendingKeyset() in Java
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
import java.io.*;
import java.util.*;
public class descendingKeySet1 {
public static void main(String[] args)
{
TreeMap<Integer, String> treemap = new TreeMap<Integer, String>();
treemap.put( 2 , "two" );
treemap.put( 0 , "zero" );
treemap.put( 3 , "three" );
treemap.put( 6 , "six" );
treemap.put( 9 , "nine" );
treemap.put( 7 , "seven" );
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
import java.io.*;
import java.util.*;
public class descendingMap {
public static void main(String[] args)
{
TreeMap<Integer, String> treemap = new TreeMap<Integer, String>();
treemap.put( 2 , "two" );
treemap.put( 0 , "zero" );
treemap.put( 3 , "three" );
treemap.put( 6 , "six" );
treemap.put( 9 , "nine" );
treemap.put( 7 , "seven" );
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.
import java.io.*;
import java.util.*;
public class descendingAppli {
public static void main(String[] args)
{
TreeMap<Integer, String> participants = new TreeMap<Integer, String>();
participants.put( 30 , "Ashty" );
participants.put( 45 , "Shavi" );
participants.put( 16 , "Vaish" );
participants.put( 15 , "Kil" );
participants.put( 11 , "Manju" );
NavigableMap<Integer, String> Ranks = participants.descendingMap();
System.out.println( "The ranks according to scores are : " );
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
Last Updated :
30 Oct, 2017
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