AbstractCollection addAll() Method in Java

The addAll() method of Java AbstractCollection is used to append all elements from a given collection to the current collection. If the collection being appended is a TreeSet, the elements are stored in sorted order, as TreeSet maintains a natural ordering. It is important to note that AbstractCollection cannot be instantiated directly, so we use Collection as the type instead. 

Example 1: Adding Elements from One Collection to Another

In this example, we append all the elements from one collection to another using the addAll() method.

Collection 1: [4, Geeks, To, TreeSet, Welcome]
Collection 2 (before addAll): []
Collection 2 (after addAll): [4, Geeks, To, TreeSet, Welcome]

Syntax of AbstractCollection addAll()

boolean addAll(Collection c);

• Parameters: The parameter "c" is a collection of any type that is to be added to the collection. 
• Return Value: The method returns "true" if it successfully appends the elements of collection c to the existing collection otherwise, it returns "false".
• Exceptions:
  • NullPointerException: If the specified collection is null.
  • UnsupportedOperationException: If the collection does not support the add() operation. 

Example 2: Using addAll() method with integer value