TreeMap ceilingEntry() and ceilingKey() methods in Java

17 Sep, 2018
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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