java 集合类 列表

Dissecting the Program

• Line 2-4 imports the collection framework classes and interfaces reside in the java.util package.
• The class hierarchy of the ArrayList is shown above. We observe that ArrayList implements List, Collection and Iterable interfaces. The Collection and Iterableinterfaces define the common behaviors of all the collection implementations. Interface Collection defines how to add and remove an element into the collection. Interface Iterable defines a mechanism to iterate or transverse through all the elements of a collection. Instead of using the interface Collection directly, it is more common to use one of its sub-interfaces, List (an ordered list supporting indexed access), Set (no duplicate elements) or Queue (FIFO, priority queues).
• In line 8, we construct an ArrayList instance, and upcast it to the List interface. This is possible as the ArrayList implements List interface. Remember that a good program operates on the interfaces instead of an actual implementation. The Collection Framework provides a set of interfaces so that you can program on these interfaces instead of the actual implementation.

https://www.ntu.edu.sg/home/ehchua/programming/java/J5c_Collection.html