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Java TreeMap lowerKey() Method with Example

TreeMap Class lowerKey() method: Here, we are going to learn about the lowerKey() method of TreeMap Class with its syntax and example.
Submitted by Preeti Jain, on February 29, 2020

TreeMap Class lowerKey() method

• lowerKey() method is available in java.util package.
• lowerKey() method is used to retrieve the greatest key element value lower than the given key element.
• lowerKey() method is a non-static method, it is accessible with the class object only and if we try to access the method with the class name then we will get an error.
• lowerKey() method may throw an exception at the time of returning lower key-value elements from this map.
  • ClassCastException: This exception may throw when the given parameter is incompatible to compare with.
  • NullPointerException: This exception may throw when the given element is null exists.

Syntax:

    public Key lowerKey(Key key_ele);

Parameter(s):

• Key key_ele – represents the key element to be tested.

Return value:

The return type of the method is Key, it retrieves the largest key element value lower than the given key element otherwise it returns null.

Example:

// Java program to demonstrate the example 
// of Key lowerKey(Key key_ele)
// method of TreeMap 

import java.util.*;

public class LowerKeyOfTreeMap {
    public static void main(String[] args) {
        // Instantiates TreeMap
        TreeMap < Integer, String > tm = new TreeMap < Integer, String > ();

        // By using put() method is
        // to put the key-value pairs in
        // treemap tm
        tm.put(1, "C");
        tm.put(4, "C++");
        tm.put(3, "Java");
        tm.put(2, "Php");

        // Display TreeMap tm
        System.out.println("tm: " + tm);

        // By using lowerKey(4) method is
        // used to return the greatest key element
        // lower than the given key element i.e. 3

        // Display Returned Key Element
        System.out.println("tm.lowerKey(): " + tm.lowerKey(4));
    }
}

Output

tm: {1=C, 2=Php, 3=Java, 4=C++}
tm.lowerKey(): 3