What is TreeMap ceilingKey() in Java with Examples?

In this article, we will learn TreeMap ceilingKey() in Java with Examples,This free JAVA tutorial for complete beginners will help you learn JAVA from scratch.

TreeMap ceilingKey() in Java with Examples️‍🔥

Q: How to use TreeMap ceilingKey() in Java with Examples in JAVA?

The ceilingKey() function of TreeMap Class returns the least key greater than or equal to the given key or null if the such a key is absent

The ceilingKey() function of TreeMap Class returns the least key greater than or equal to the given key or null if the such a key is absent.

Syntax:

public K ceilingKey(K key)

Parameters: This method accepts a mandatory parameter key which is the key to be searched for.

Return Value: This method returns the least key which is greater than or equal to the given key value.
If such a key is absent, null is returned.

Exceptions: This method throws following exceptions:

ClassCastException – Thrown if the specified key can’t be compared with the given key values.
NullPointerException – Thrown if the given key is null and the map uses natural ordering or the comparator does not permit null values.

Below are the examples to illustrate ceilingKey() method:

Program 1: To demonstrate use of ceilingKey() method for a TreeMap with comparator

import java.util.*; 
  
public class Main { 
    public static void main(String[] args) 
    { 
  
        // creating tree map 
        NavigableMap<Integer, String> 
            treemap = new TreeMap<Integer, 
                                  String>((a, b) 
                                              -> ((a > b) 
                                                      ? 1
                                                      : ((a == b) 
                                                             ? 0
                                                             : -1))); 
  
        // populating tree map 
        treemap.put(1, " A "); 
        treemap.put(2, " B "); 
        treemap.put(3, " C "); 
        treemap.put(4, " D "); 
        treemap.put(6, " E "); 
        try { 
            System.out.println("Ceiling key entry for 5: "
                               + treemap.ceilingKey(5)); 
        } 
        catch (Exception e) { 
            System.out.println("Exception: " + e); 
        } 
    } 
} 

Output:

Ceiling key entry for 5: 6

Program 2: To demonstrate use of ceilingKey() method for a TreeMap without any comparator

import java.util.*; 
  
public class Main { 
    public static void main(String[] args) 
    { 
  
        // creating tree map 
        NavigableMap<Integer, String> 
            treemap = new TreeMap<Integer, String>(); 
  
        // populating tree map 
        treemap.put(1, " A "); 
        treemap.put(2, " B "); 
        treemap.put(3, " C "); 
        treemap.put(4, " D "); 
        treemap.put(6, " E "); 
        treemap.put(7, " F "); 
  
        // Since 6 is the least value greater than 5, 
        // it is returned as the key. 
        System.out.println("Ceiling key entry for 5: "
                           + treemap.ceilingKey(5)); 
    } 
} 

Output:

Ceiling key entry for 5: 6

Program 3: To demonstrate use of ceilingKey() method when it will return null

import java.util.*; 
  
public class Main { 
    public static void main(String[] args) 
    { 
  
        // creating tree map 
        NavigableMap<Integer, String> 
            treemap = new TreeMap<Integer, String>(); 
  
        // populating tree map 
        treemap.put(1, " A "); 
        treemap.put(2, " B "); 
        treemap.put(3, " C "); 
        treemap.put(4, " E "); 
        treemap.put(5, " D "); 
  
        // Since 10 is not present in the Map 
        // and neither any Key is present greater than 10 
        // Hence this will return null 
        System.out.println("Ceiling key entry for 10: "
                           + treemap.ceilingKey(10)); 
    } 
} 

Output:

Ceiling key entry for 10: null

Program 4: To show NullPointerException

import java.util.*; 
  
public class Main { 
    public static void main(String[] args) 
    { 
  
        // creating tree map 
        TreeMap<Integer, String> 
            treemap = new TreeMap<Integer, String>(); 
  
        // populating tree map 
        treemap.put(2, " two "); 
        treemap.put(1, " one "); 
        treemap.put(3, " three "); 
        treemap.put(6, " six "); 
        treemap.put(5, " five "); 
  
        try { 
            // returns a NullPointerException 
            // as key value can't be null 
            // because of natural ordering 
            System.out.println("Ceiling key entry for null value : "
                               + treemap.ceilingKey(null)); 
        } 
        catch (Exception e) { 
            System.out.println("Exception: " + e); 
        } 
    } 
} 

Output:

Exception: java.lang.NullPointerException

Program 5: To demonstrate ClassCastException

import java.util.*; 
  
public class Main { 
    public static void main(String[] args) 
    { 
  
        // creating tree map 
        NavigableMap<Object, String> 
            treemap = new TreeMap<Object, String>(); 
  
        // populating tree map 
        treemap.put(1, " A "); 
        treemap.put(2, " B "); 
        treemap.put(3, " C "); 
        treemap.put(4, " E "); 
        treemap.put(5, " D "); 
  
        try { 
            // returns ClassCastException 
            // as we cannot compare a String object with an Integer object 
            System.out.println("Ceiling key entry for \"asd\": "
                               + treemap.ceilingKey(new String("asd"))); 
        } 
        catch (Exception e) { 
            System.out.println("Exception: " + e); 
        } 
    } 
} 

Output:

Exception: java.lang.ClassCastException: 
           java.lang.Integer cannot be cast to java.lang.String