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
// 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
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