TreeMap floorKey() in Java with Examples

Pre-requisite: TreeMap in Java

The floorKey() method is used to return the greatest key less than or equal to given key from the parameter.

Syntax:

public K floorKey(K key)

Parameter: This method accepts a mandatory parameter key which is the key to be matched.

Return Value: The method call returns the greatest key less than or equal to key, or null if there is no such key.

Exception: This method throws following exceptions:

• ClassCastException: When the specified key cannot be compared with the key available in Map.
• NullPointerException: When the specified key in map is null and it uses natural
  ordering which means, comparator does not permit null keys.

Below are examples to illustrate the use of floorKey() method:

Example 1:

// Java program to demonstrate floorKey() method

import java.util.TreeMap;

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

        // create an empty TreeMap
        TreeMap<Integer, String> numMap = new TreeMap<Integer, String>();

        // Insert the values
        numMap.put(6, "Six");
        numMap.put(1, "One");
        numMap.put(5, "Five");
        numMap.put(3, "Three");
        numMap.put(8, "Eight");
        numMap.put(10, "Ten");

        // Print the Values of TreeMap
        System.out.println("TreeMap: " + numMap.toString());

        // Get the greatest key mapping of the Map

        // As here 11 is not available it returns 10
        // because ten is less than 11
        System.out.print("Floor Entry of Element 11 is: ");
        System.out.println(numMap.floorKey(11));

        // This will give null
        System.out.print("Floor Entry of Element 0 is: ");
        System.out.println(numMap.floorKey(0));
    }
}

Output:

TreeMap: {1=One, 3=Three, 5=Five, 6=Six, 8=Eight, 10=Ten}
Floor Entry of Element 11 is: 10
Floor Entry of Element 0 is: null

Example 2: To demonstrate NullPointerException

// Java program to demonstrate floorKey() method

import java.util.TreeMap;

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

        // create an empty TreeMap
        TreeMap<Integer, String>
            numMap = new TreeMap<Integer, String>();

        // Insert the values
        numMap.put(6, "Six");
        numMap.put(1, "One");
        numMap.put(5, "Five");
        numMap.put(3, "Three");
        numMap.put(8, "Eight");
        numMap.put(10, "Ten");

        // Print the Values of TreeMap
        System.out.println("TreeMap: " + numMap.toString());

        try {
            // Passing null as parameter to floorKey()
            // This will throw exception
            System.out.println(numMap.floorKey(null));
        }
        catch (Exception e) {
            System.out.println("Exception: " + e);
        }
    }
}

Output:

TreeMap: {1=One, 3=Three, 5=Five, 6=Six, 8=Eight, 10=Ten}
Exception: java.lang.NullPointerException