Java: Get the greatest key strictly less than the given key

Last update on May 23 2025 13:08:45 (UTC/GMT +8 hours)

17. Get Lower Key in TreeMap

Write a Java program to get 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 Example17 {  
         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.lowerKey(10));
  System.out.println("Checking the entry for 20: ");
  System.out.println("Key(s): " + tree_map1.lowerKey(20));
  System.out.println("Checking the entry for 70: ");
  System.out.println("Key(s): " + tree_map1.lowerKey(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                                                             
Checking the entry for 70:                                             
Key(s): 60

For more Practice: Solve these Related Problems:

Write a Java program to use lowerKey() to retrieve the greatest key strictly less than a given key.
Write a Java program to implement a custom iterative method to find the largest key less than a specified value in a TreeMap.
Write a Java program to compare lowerKey()’s output with the result from converting the key set to a sorted list and selecting the predecessor.
Write a Java program to handle null output from lowerKey() and print a fallback message if no such key exists.

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Java Code Editor:

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