SortedMap tailMap() method in Java

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:

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// 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));
    }
}

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Output:

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

Program 2:

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// 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"));
    }
}

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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)



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