Método TreeMaphigherKey() en Java con ejemplos

El métodohigherKey() de la clase java.util.TreeMap se usa para devolver la clave mínima estrictamente mayor que la clave dada, o nulo si no existe tal clave.
Sintaxis: 
 

public K higherKey(K key)

Parámetros: Este método toma como parámetro la clave k .
Valor devuelto: este método devuelve la clave mínima mayor que la clave, o nulo si no existe tal clave.
Excepción: este método lanza la excepción NullPointerException si la clave especificada es nula y este mapa usa un orden natural, o su comparador no permite claves nulas.
A continuación se muestran los ejemplos para ilustrar el método highKey()
Ejemplo 1: 
 

// Java program to demonstrate
// higherKey() method
// for <Integer, String>
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv) throws Exception
    {
        try {
 
            // creating object of TreeMap<Integer, String>
            TreeMap<Integer, String>
                treemap = new TreeMap<Integer, String>();
 
            // populating tree map
            treemap.put(1, "One");
            treemap.put(2, "Two");
            treemap.put(3, "Three");
            treemap.put(4, "Four");
            treemap.put(5, "Five");
 
            // printing the TreeMap
            System.out.println("TreeMap: " + treemap);
 
            // getting higher key value for 3
            // using higherKey() method
            int value = treemap.higherKey(3);
 
            // printing the value
            System.out.println("The higherKey value "
                               + " for 3: " + value);
        }
 
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

TreeMap: {1=One, 2=Two, 3=Three, 4=Four, 5=Five}
The higherKey value  for 3: 4

Ejemplo 2: para NullPointerException 
 

// Java program to demonstrate
// higherKey() method
// for NullPointerException
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv) throws Exception
    {
        try {
 
            // creating object of TreeMap<Integer, String>
            TreeMap<Integer, String>
                treemap = new TreeMap<Integer, String>();
 
            // populating tree map
            treemap.put(1, "One");
            treemap.put(2, "Two");
            treemap.put(3, "Three");
            treemap.put(4, "Four");
            treemap.put(5, "Five");
 
            // printing the TreeMap
            System.out.println("TreeMap: " + treemap);
 
            // getting higher key value for null
            // using higherKey() method
            System.out.println("Trying to get higherKey"
                               + " value for null");
 
            int value = treemap.higherKey(null);
 
            // printing the value
            System.out.println("Value is: " + value);
        }
 
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

TreeMap: {1=One, 2=Two, 3=Three, 4=Four, 5=Five}
Trying to get higherKey value for null
Exception thrown : java.lang.NullPointerException