addAll

AddAll is a common operation in collection libraries that copies all elements from one collection into another. It is designed to merge two collections efficiently by appending the contents of the source collection to the end of the destination collection, preserving the source order for elements.

In the Java Collections Framework, addAll is defined on the Collection interface as boolean addAll(Collection<? extends E> c). The List interface also provides boolean addAll(int index, Collection<? extends E> c) to insert elements starting at a given position. The method returns true if the destination collection was modified; it returns false if the input collection is empty.

Null handling and errors: The method throws NullPointerException if the input collection is null. If the destination collection does not permit nulls and the input contains null elements, a NullPointerException may be thrown. UnsupportedOperationException may be thrown by collections that do not support the operation.

Semantics: addAll does not remove elements from the source or perform deduplication; the resulting collection contains all elements from the source in their original order, followed by any existing elements in the destination. Duplicates are allowed according to the destination’s policy.

Complexity and considerations: The operation is typically linear in the number of added elements. Some implementations may optimize by resizing internal storage, but characteristics depend on the concrete collection type. If the destination is a List, adding at a specific index may require shifting existing elements.

Other languages: In Kotlin, addAll functions similarly; in Python, the equivalent concepts are extend (for lists) or update (for sets), reflecting differences in collection semantics.