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Java Collection, TreeMap Exercises: Get the portion of a map whose keys are strictly less than a given key

Java Collection, TreeMap Exercises: Exercise-13 with Solution

Write a Java program to get the portion of a map whose keys are strictly less than a given key.

Sample Solution:-

Java Code:

import java.util.*;
import java.util.Map.Entry;  
public class Example13 {  
       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.headMap(10));
  System.out.println("Checking the entry for 30: ");
  System.out.println("Key(s): " + tree_map1.headMap(30));
  System.out.println("Checking the entry for 70: ");
  System.out.println("Key(s): " + tree_map1.headMap(70));
 }
}

Sample Output:

Orginal TreeMap content: {10=Red, 20=Green, 40=Black, 50=White, 60=Pink
}                                                                      
Checking the entry for 10:                                             
Key(s): {}                                                             
Checking the entry for 30:                                             
Key(s): {10=Red, 20=Green}                                             
Checking the entry for 70:                                             
Key(s): {10=Red, 20=Green, 40=Black, 50=White, 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