Java TreeMap - lowerKey() Method

The java.util.TreeMap.lowerKey() method returns the greatest key strictly less than the given key, or null if there is no such key.

Syntax

public K lowerKey(K key)

Here, K is the type of key maintained by the container.

Parameters

Return Value

Returns the greatest key less than key, or null if there is no such key.

Exception

• Throws ClassCastException, if the specified key cannot be compared with the keys currently in the map.
• Throws NullPointerException, if the specified key is null and this map uses natural ordering, or its comparator does not permit null keys.

Example:

In the example below, the java.util.TreeMap.lowerKey() method returns the greatest key less than the given value.

import java.util.*;

public class MyClass {
  public static void main(String[] args) {
    //creating a treemap
    TreeMap<Integer, String> MyMap = new TreeMap<Integer, String>();

    //populating the map
    MyMap.put(102, "John");
    MyMap.put(103, "Marry");
    MyMap.put(101, "Kim");
    MyMap.put(104, "Jo");
    MyMap.put(105, "Sam");

    //printing the map
    System.out.println("MyMap contains: " + MyMap); 

    //printing the greatest key less than 103.
    System.out.println("Lower Key for 103 is: " + MyMap.lowerKey(103));     
  }
}

The output of the above code will be:

MyMap contains: {101=Kim, 102=John, 103=Marry, 104=Jo, 105=Sam}
Lower Key for 103 is: 102