Collections Collection framework

1. Several features of the Collection framework: high performance, easy scalability, interoperability, and support for integrated standard arrays. (In fact, what is called a container in C is called a collection in Java)

2. Iterator: provides a common standard way to access a set element, that is, one access at a time. Therefore, the iterator provides a method to list the content of a set. In addition, any set implements the iterator interface.

3. The Collection framework also includes ing interfaces and classes. Maps is used to store key/value pairs.

4. Collection interface: The basis of the Collection framework, including add, addall, clear, contains, containsall, equals, hashcode, isempty, iterator, remove, removeall, retainall, size, toarray and other basic methods.

5. List interface: uses a 0-based index, which can contain the same elements.

6. Set interface: The set cannot have the same elements.

7. Sortedset interface: extends the set interface and declares it as a set in ascending order.

8. Arraylist class: extends the javasactlist interface to implement the list interface. In Java, the array length is fixed. Once an array is created, the length cannot be changed.