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Java Collection, TreeMap Exercises: Get a key-value mapping associated with the greatest key strictly less than the given key

Java Collection, TreeMap Exercises: Exercise-16 with Solution

Write a Java program to get a key-value mapping associated with the greatest key strictly less than the given key. Return null if there is no such key.

Sample Solution:-

Java Code:

import java.util.*;
import java.util.Map.Entry;  
public class Example16 {  
       public static void main(String args[]){  
  
    // Create a tree map
   TreeMap< Integer, String > tree_map1 = new TreeMap< Integer, String >();      
  
  // Put elements to the map 
  tree_map1.put(10, "Red");
  tree_map1.put(20, "Green");
  tree_map1.put(40, "Black");
  tree_map1.put(50, "White"); 
  tree_map1.put(60, "Pink"); 
    
      System.out.println("Orginal TreeMap content: "+tree_map1);
	  System.out.println("Checking the entry for 10: ");
      System.out.println("Key(s): "+tree_map1.lowerEntry(10));  
	  System.out.println("Checking the entry for 20: ");
      System.out.println("Key(s): "+tree_map1.lowerEntry(20));  
	  System.out.println("Checking the entry for 70: ");
      System.out.println("Key(s): "+tree_map1.lowerEntry(70));  
    }
}

Sample Output:

Orginal TreeMap content: {10=Red, 20=Green, 40=Black, 50=White, 60=Pink
}                                                                      
Checking the entry for 10:                                             
Key(s): null                                                           
Checking the entry for 20:                                             
Key(s): 10=Red                                                         
Checking the entry for 70:                                             
Key(s): 60=Pink

Java Code Editor:

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Java: Tips of the Day

getEnumMap

Converts to enum to Map where key is the name and value is Enum itself.

public static <E extends Enum<E>> Map<String, E> getEnumMap(final Class<E> enumClass) {
    return Arrays.stream(enumClass.getEnumConstants())
            .collect(Collectors.toMap(Enum::name, Function.identity()));
}

Ref: https://bit.ly/3xXcFZt