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

Last update on May 23 2025 13:08:11 (UTC/GMT +8 hours)

13. Get Head Map with Keys Less Than Given Key

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}

For more Practice: Solve these Related Problems:

Write a Java program to use headMap() on a TreeMap to extract all entries with keys strictly less than a given key and print the sub-map.
Write a Java program to iterate over the sub-map obtained from headMap() and compute a sum of its values.
Write a Java program to filter a TreeMap using Java streams to obtain a new map containing keys less than a specified value.
Write a Java program to remove entries from a TreeMap with keys less than a given threshold using headMap() and then print the modified map.

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Java Code Editor:

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