TreeSet addAll(Collection) in Java

addAll(Collection): This method is available in java.util.TreeSet class of Java.

Syntax:

boolean java.util.TreeSet.addAll(Collection<? extends String> c)

This method takes one argument. This method adds all of the elements in the specified collection to this set.

Parameters: One parameter is required for this method.

c: a collection containing elements to be added to this set.

Returns: true if this set changed as a result of the call.

Throws:

1. ClassCastException - if the elements provided cannot be compared with the elements currently in the set.

2. NullPointerException - if the specified collection is null or if any element is null and this set uses natural ordering, or its comparator does not permit null elements

Approach 1: When no exception

Java

import java.util.TreeSet;

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

        TreeSet<String> treeSet = new TreeSet<String>();
        TreeSet<String> c = new TreeSet<String>();
        c.add("Hello");
        c.add("Java");

        System.out.println(treeSet.addAll(c));
    }
}

Output:

true

Approach 2: NullPointerException 

Java

import java.util.TreeSet;

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

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

        System.out.println(treeSet.addAll(c));
    }
}

Output:

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "java.util.Collection.size()" because "c" is null
	at java.base/java.util.TreeSet.addAll(TreeSet.java:300)