Java-preliminary Understanding-Common Object API (collection framework-map collection common subclass objects)

One.

I'm done with the map collection, by the way, little things.

A common subclass of the map collection:

Hashtable research is data structure, hash in 1.0 out, there is no table. At that time, single-column collections were only vectors, and double-row collections were hashtable. The internal structure is a hash table. is synchronous. HashMap and Hashtable are different, the efficiency is no longer said. is a HashMap API note that is not synchronized.

Hashtable, it does not support null keys and null values. The difference between them during the interview.

The system above is similar to a set system, which is set set, HashSet and TreeSet, see. You can save a couple at a time. Just let the value be a uniform object and it's done. I just manipulate the key, which is the set set. The underlying code of the set set is the map collection to implement, in fact, the map has been able to solve the problem. Why do we have set? It is to ensure that the set that is generated by the uniqueness of the element in a single-column collection is for more convenient application, otherwise the map will be done.

Hashtable will not demonstrate, in fact, we will use. Because it has sub-class, the use of high frequency, is the properties.

Properties are typically used for property sets, which are used to store information about a configuration file. A configuration file is typically a key and a value. Not currently, as it is combined with I/O technology to work. This is an object, a container, that is in the map collection.

Java-preliminary Understanding-Common Object API (collection framework-map collection common subclass objects)