SortedMap tailMap() method in Java

Last Updated : 26 Nov, 2018

The tailMap() method of SortedMap interface in Java is used to return a view of the portion of this map whose keys are greater than or equal to fromKey.

The map returned by this method is backed by this map, so changes in the returned map are reflected in this map, and vice-versa.
The map returned by this method supports all optional map operations that this map supports.

Note: The map returned by this method will throw an IllegalArgumentException if an attempt is made to insert a key outside its range.

Syntax:

SortedMap<K, V> tailMap(K fromKey)

Where, K is the type of key maintained by this Set and V is the type of values associated with the Key.

Parameters: This function accepts a single parameter fromKey which represents high endpoint (exclusive) of the keys in the returned map.

Return Value: It returns a view of the portion of this map whose keys are strictly greater than or equal to fromKey.

Exception:

ClassCastException: If the parameter fromKey is not compatible with this map’s comparator (or, if the map has no comparator, if fromKey does not implement Comparable).
NullPointerException: If the parameter fromKey is null and this map does not permit null keys.
IllegalArgumentException: If this map itself has a restricted range, and fromKey lies outside the bounds of the range

Below programs illustrate the above method:

Program 1:

// A Java program to demonstrate 
// working of SortedSet 
import java.util.*; 
  
public class Main { 
    public static void main(String[] args) 
    { 
        // Create a TreeSet and inserting elements 
        SortedMap<Integer, String> mp = new TreeMap<>(); 
  
        // Adding Element to SortedSet 
        mp.put(1, "One"); 
        mp.put(2, "Two"); 
        mp.put(3, "Three"); 
        mp.put(4, "Four"); 
        mp.put(5, "Five"); 
  
        // Returning the key greater 
        // than or equal to 2 
        System.out.print("Last Key in the map is : "
                         + mp.tailMap(2)); 
    } 
} 

Output:

Last Key in the map is : {2=Two, 3=Three, 4=Four, 5=Five}

Program 2:

// A Java program to demonstrate 
// working of SortedSet 
import java.util.*; 
  
public class Main { 
    public static void main(String[] args) 
    { 
        // Create a TreeSet and inserting elements 
        SortedMap<String, String> mp = new TreeMap<>(); 
  
        // Adding Element to SortedSet 
        mp.put("One", "Geeks"); 
        mp.put("Two", "For"); 
        mp.put("Three", "Geeks"); 
        mp.put("Four", "Code"); 
        mp.put("Five", "It"); 
  
        // Returning the key greater 
        // than or equal to 
        System.out.print("Last Key in the map is : "
                         + mp.tailMap("D")); 
    } 
} 

Output:

Last Key in the map is : {Five=It, Four=Code, One=Geeks, Three=Geeks, Two=For}

Reference: https://docs.oracle.com/javase/10/docs/api/java/util/SortedMap.html#tailMap(K)

SortedMap firstKey() method in Java

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