java.util.TreeMap.lowerKey() Method


The lowerKey(K key) method is used to return the greatest key strictly less than the given key, or null if there is no such key.


Following is the declaration for java.util.TreeMap.lowerKey() method.

public K lowerKey(K key)


key − This is the key to be checked.

Return Value

The method call returns the greatest key less than key, or null if there is no such key.


  • ClassCastException − This exception is thrown if the specified key cannot be compared with the keys currently in the map.

  • NullPointerException − This exception is thrown if the specified key is null and this map uses natural ordering, or its comparator does not permit null keys.


The following example shows the usage of java.util.TreeMap.lowerKey()

package com.tutorialspoint;

import java.util.*;

public class TreeMapDemo {
   public static void main(String[] args) {

      // creating tree map 
      TreeMap<Integer, String> treemap = new TreeMap<Integer, String>();

      // populating tree map
      treemap.put(2, "two");
      treemap.put(1, "one");
      treemap.put(3, "three");
      treemap.put(6, "six");
      treemap.put(5, "five");

      // getting lower key  
      System.out.println("Checking lower key");
      System.out.println("Value is: "+ treemap.lowerKey(5));

Let us compile and run the above program, this will produce the following result.

Checking lower key
Value is: 3
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