ceilingKey

1- public K ceilingKey(K key) {}
2-return key .
3-  Gets the entry corresponding to the specified key;
4-if no such entry exists, returns the entry for the least key greater than the specified key;
5-if no such entry exists (i.e., the greatest key in the Tree is less than the specified key), returns null

Example:
package com.example;

import java.util.TreeMap;

public class Test2 {
    public static void main(String[] args) {
        TreeMap treeExample=new TreeMap();
        treeExample.put(1, "AAA");
        treeExample.put(2, "BBB");
        treeExample.put(4, "DDD");
        System.out.println(treeExample.ceilingKey(1));
        System.out.println(treeExample.ceilingKey(3));
        System.out.println(treeExample.ceilingKey(6));
       
    }
}
 

Out Put:
1
4
null.