TreeMap ceilingEntry() and ceilingKey() methods in Java

There are two variants of ceilingEntry() in Java.util.TreeMap, both are discussed in this article.

1. ceilingEntry(K Key) : It is used to return a key-value mapping associated with the least key greater than or equal to the given key, or null if there is no such key.

Syntax : 
public Map.Entry ceilingEntry(K key)
Parameters : 
key : The key to be matched.
Return Value : 
It returns the entry with the least key greater than or equal to key, and null if 
there is no such key.
Exception : 
ClassCastException : It throws the exception if the specified key cannot be compared
with the keys currently in the map.
NullPointerException : It throws the exception if the specified key is null. 

// Java code to demonstrate the working of
// ceilingEntry()

import java.io.*;
import java.util.*;

public class ceilingEntry1 {

  public static void main(String[] args) {

  // Declaring the tree map of Integer and String
  TreeMap<Integer, String> treemap = new TreeMap<Integer, String>();

  // assigning the values in the tree map
  // using put()
  treemap.put(2, "two");
  treemap.put(7, "seven");
  treemap.put(3, "three");

  // Use of ceilingEntry()
  // returns 7=seven ( next greater key-value)
  System.out.println("The next greater key-value of 5 is : " + treemap.ceilingEntry(5));

  // returns "null" as no value present
  // greater than or equal to number
  System.out.println("The next greater key-value of 8 is : " + treemap.ceilingEntry(8));

  }
}

Output:

The next greater key-value of 5 is : 7=seven
The next greater key-value of 8 is : null

2. ceilingKey(K key) : This has also the same work as that of the upper one but the only difference is that it does not contains the mapped-keys.It simply returns the least key greater or equal to the given key, else returns NULL.

Syntax : 
public K ceilingKey(K key)
Parameters : 
key : The key to be matched.
Return Value : 
It returns the entry with the least key greater than or equal to key, and null 
if there is no such key.
Exception:
ClassCastException : It throws the exception if the specified key cannot be compared
with the keys currently in the map.
NullPointerException : It throws the exception if the specified key is null. 

// Java code to demonstrate the working of
// ceilingKey()

import java.io.*;
import java.util.*;

public class ceilingKey1 {

  public static void main(String[] args) {

  // Declaring the tree map of Integer and String
  TreeMap<Integer, String> treemap = new TreeMap<Integer, String>();

  // assigning the values in the tree map
  // using put()
  treemap.put(2, "two");
  treemap.put(7, "seven");
  treemap.put(3, "three");

  // Use of ceilingKey()
  // returns 7 ( next greater key)
  System.out.println("The next greater key of 5 is : " + treemap.ceilingKey(5));

  // returns "null" as no key present
  // greater than or equal to number
  System.out.println("The next greater key of 8 is : " + treemap.ceilingKey(8));

  }
}

Output:

The next greater key of 5 is : 7
The next greater key of 8 is : null

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