TreeMap : higherKey (K key) : get the least key strictly greater than the given key

public K higherKey(K key)

Returns the least key strictly greater than the given key, or null if there is no such key.

import java.util.*;

class TreeMapHigherKey{
 public static void main(String args[]){
  TreeMap<Integer, String> myMap;
  Integer myKey;
  
  myMap = new TreeMap<> ();
  
  /* Add Elements to myMap */
  myMap.put(2, "w");
  myMap.put(4, "wx");
  myMap.put(6, "wxy");
  myMap.put(8, "wxyz");
  
  myKey = myMap.higherKey(4);
  
  System.out.println("Elements in myMap are");
  System.out.println(myMap);
  
  System.out.println("Higher key for the key 4 is ");
  System.out.println(myKey);  
  
  myKey = myMap.higherKey(8);
  
  System.out.println("Higher key for the key 8 is ");
  System.out.println(myKey); 
 }
}

Output

Elements in myMap are
{2=w, 4=wx, 6=wxy, 8=wxyz}
Higher key for the key 4 is
6
Higher key for the key 8 is
null

1. Throws NullPointerException if the specified key is null and this map uses natural ordering, or its comparator does not permit null keys

import java.util.*;

class TreeMapHigherKeyNullPointer{
 public static void main(String args[]){
  TreeMap<Integer, String> myMap;
  Integer myKey;
  
  myMap = new TreeMap<> ();
  
  /* Add Elements to myMap */
  myMap.put(2, "w");
  myMap.put(4, "wx");
  myMap.put(6, "wxy");
  myMap.put(8, "wxyz");
  
  System.out.println("Elements in myMap are");
  System.out.println(myMap);
  
  System.out.println("Higher key for the key null is ");
  myKey = myMap.higherKey(null); 
 }
}

  

Output

Elements in myMap are
{2=w, 4=wx, 6=wxy, 8=wxyz}
Higher key for the key null is
Exception in thread "main" java.lang.NullPointerException
        at java.util.TreeMap.compare(TreeMap.java:1290)
        at java.util.TreeMap.getHigherEntry(TreeMap.java:463)
        at java.util.TreeMap.higherKey(TreeMap.java:777)
        at TreeMapHigherKeyNullPointer.main(TreeMapHigherKeyNullPointer.java:20)

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