The collection framework for Java

List and set under the 1.Collection interface

HashMap and TreeMap under the 2.Map interface

The difference between List and set. The List allows duplicate elements to exist, and set cannot have duplicate elements. Duplicate elements in set are not allowed to be determined by the hashcode and Equals methods, and equals are compared only when hashcode is the same.

The elements of the hashmap are unordered, and the elements inside the TreeMap are ordered (natural order).

It is necessary to implement the interface comparator or comparable to implement the ordering.

Comparable interface Implementation method

CompareTo (T o)

Comparatoe requires an interface implementation method
compare(T o1, T o2)

equals (Object obj)

The collection framework for Java