TreeSet tailSet(K, boolean) in Java

tailSet(K, boolean): This method is available in java.util.TreeSet class of Java.

Syntax:

NavigableSet<K> java.util.TreeSet.tailSet(K fromElement, boolean inclusive)

This method takes two arguments. This method returns a view of the portion of this set whose elements are greater than (or equal to, if inclusive is true) fromElement.

Note: The returned set is backed by this set, so changes in the returned set are reflected in this set, and vice-versa.

Parameters: Two parameters are required for this method.

fromElement: low endpoint of the returned set.

inclusive: true if the low endpoint is to be included in the returned view.

Returns: a view of the portion of this set whose elements are greater than or equal to fromElement

Throws:

1. ClassCastException - if fromElement is not compatible with this set's comparator.

2. NullPointerException - if fromElement is null and this set uses natural ordering, or its comparator does not permit null elements.

3. IllegalArgumentException - if this set itself has a restricted range, and fromElement lies outside the bounds of the range.

Approach 1: When no exception

Java

import java.util.TreeSet;

public class TreeSettailSet2 {
    public static void main(String[] args) {

        TreeSet<String> treeSet = new TreeSet<String>();

        treeSet.add("Hello");
        treeSet.add("Java");
        treeSet.add("Program");
        treeSet.add("C++");
        String fromElement = "Java";

        boolean inclusive = true;

        System.out.println(treeSet.tailSet(fromElement,
                                           inclusive));

    }
}

Output:

[Java, Program]

Approach 2: NullPointerException 

Java

import java.util.TreeSet;

public class TreeSettailSet2 {
    public static void main(String[] args) {

        TreeSet<String> treeSet = new TreeSet<String>();

        treeSet.add("Hello");
        treeSet.add("Java");
        treeSet.add("Program");
        treeSet.add("C++");
        String fromElement = null;

        boolean inclusive = true;

        System.out.println(treeSet.tailSet(fromElement, 
                                            inclusive));

    }
}

Output:

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "java.lang.Comparable.compareTo(Object)" because "k1" is null
	at java.base/java.util.TreeMap.compare(TreeMap.java:1563)
	at java.base/java.util.TreeMap$NavigableSubMap.<init>(TreeMap.java:1644)
	at java.base/java.util.TreeMap$AscendingSubMap.<init>(TreeMap.java:2129)
	at java.base/java.util.TreeMap.tailMap(TreeMap.java:1210)
	at java.base/java.util.TreeSet.tailSet(TreeSet.java:348)