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

Last update on May 23 2025 13:08:47 (UTC/GMT +8 hours)

14. Get Head Map with Optional Inclusive Key

Write a Java program to get the portion of this map whose keys are less than (or equal to, if inclusive is true) a given key.

Sample Solution:-

Java Code:

import java.util.*;
import java.util.Map.Entry;  
public class Example14 {  
       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, true));
  System.out.println("Checking the entry for 20: ");
  System.out.println("Key(s): " + tree_map1.headMap(20, true));
  System.out.println("Checking the entry for 70: ");
  System.out.println("Key(s): " + tree_map1.headMap(70, true));
 }
}

Sample Output:

Orginal TreeMap content: {10=Red, 20=Green, 40=Black, 50=White, 60=Pink
}                                                                      
Checking the entry for 10:                                             
Key(s): {10=Red}                                                       
Checking the entry for 20:                                             
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(key, true) on a TreeMap to retrieve all entries with keys less than or equal to a specified key.
Write a Java program to iterate over a sub-map obtained from headMap(key, true) and print each key-value pair.
Write a Java program to compare the sizes of sub-maps obtained using headMap(key, true) and headMap(key, false) for a given key.
Write a Java program to filter a TreeMap’s entries using a lambda expression for keys ≤ a given value and collect the result into a new map.

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