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Java.util.TreeMap.floorEntry() and floorKey() in Java
  • Difficulty Level : Basic
  • Last Updated : 24 Nov, 2017
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Finding greatest number less than given value is used in many a places and having that feature in a map based container is always a plus. Java.util.TreeMap also offers this functionality using floor() function. There are 2 variants, both are discussed below.

1. floorEntry() : It returns a key-value mapping associated with the greatest key less than or equal to the given key, or null if there is no such key.

Parameters:
key : This is the key to be matched.
Return Value:
It returns an entry with the greatest key less than or equal to key,
or null if there is no such key.
Exception:
ClassCastException : This exception is thrown if the specified
key cannot be compared with the keys currently in the map.
NullPointerException : This exception is thrown if the specified
key is null and this map uses natural ordering, or its comparator does not permit null keys.




// Java code to demonstrate the working
// of floorEntry()
import java.io.*;
import java.util.*;
public class floorEntry {
    public static void main(String[] args)
    {
  
        // Declaring the tree map of Integer and String
        TreeMap<Integer, String> tmp = new TreeMap<Integer, String>();
  
        // assigning the values in the tree map
        // using put()
        tmp.put(10, "ten");
        tmp.put(7, "seven");
        tmp.put(19, "nineteen");
        tmp.put(3, "three");
  
        // use of floorEntry()
        // displays the floor value of 6
        // prints 3=three
        System.out.println("The greatest key-value less than 6 is : " 
        + tmp.floorEntry(6));
    }
}

Output:

The greatest key-value less than 6 is : 3=three

2. floorKey() : It returns the greatest key less than or equal to the given key, or null if there is no such key.

Parameters:
key : This is the key to be matched.
Return Value:
It returns an entry with the greatest key less than or equal to key, or
null if there is no such key.
Exception:
ClassCastException : This exception is thrown if the specified
key cannot be compared with the keys currently in the map.
NullPointerException : This exception is thrown if the specified key
is null and this map uses natural ordering, or its comparator does not permit null keys.




// Java code to demonstrate the working
// of floorKey()
import java.io.*;
import java.util.*;
public class floorKey {
    public static void main(String[] args)
    {
  
        // Declaring the tree map of Integer and String
        TreeMap<Integer, String> tmp = new TreeMap<Integer, String>();
  
        // assigning the values in the tree map
        // using put()
        tmp.put(10, "ten");
        tmp.put(7, "seven");
        tmp.put(19, "nineteen");
        tmp.put(3, "three");
  
        // use of floorKey()
        // displays the floor key of
        // prints 3
        System.out.println("The greatest key less than 6 is : "
        + tmp.floorKey(6));
    }
}

Output:

The greatest key less than 6 is : 3

Practical Application : The possible applications of this functions are aplenty. Starting from maximum distance with given petrol or possible dishes with given ingredients. Former one is discussed in code below.




// Java code to demonstrate the application
// of floorKey() and floorEntry
import java.io.*;
import java.util.*;
public class floorappli {
    public static void main(String[] args)
    {
  
        // Declaring the tree map of Integer and String
        TreeMap<Integer, String> destin = new TreeMap<Integer, String>();
  
        // assigning the km with destination
        // from beginning
        // using put()
        destin.put(10, "Delhi");
        destin.put(7, "Gurgaon");
        destin.put(19, "Noida");
        destin.put(3, "Ring Road");
  
        // Entering the available Petrol (consider 1km/litre)
        int petr = 12;
  
        // Maximum place you can reach
        System.out.println("The maximum place you can reach with given petrol : "
        + destin.floorEntry(petr));
    }
}

Output:

The maximum place you can reach with given petrol : 10=Delhi

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