Java ArrayList.addAll() is a method in the Java ArrayList class that adds all elements from another collection or array to the list. It appends the elements to the end of the list, ensuring that the original list is modified in place. Introduced in Java 1995 with Java 1.2, addAll() is commonly used for merging lists or copying elements between collections in Java applications.

https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html