Collections Framework in Java Notes

1. The concept and function of collections:

1. Concept: A collection is a tool class and a container that can store any number of objects with the same attributes;

2 .Function: 1). Organize data inside the class

2). Simple and fast search for a large number of entries

3). Some collection interfaces provide a series of Elements are arranged in order, and elements can be quickly inserted or deleted in the order

4). Some collections provide mapping relationships, and the corresponding unique objects can be quickly found through the key area. .

2. Java collection framework system:

1.Collection interface:

(1) List

1.ArrayList implementation class:

*The elements are ordered and can be repeated, which is called a sequence

*Can accurately control the insertion of an element or the deletion of an element at a certain position

*The bottom layer is implemented by an array

2.LinkedList implementation class

(2)Set

1.HashSet implementation class

*Set is an element that does not need to be repeated and cannot be repeated. It is called For the set

2.Map interface

(1) HashMap

*Map provides a mapping relationship, in which the elements are key-value pairs (key, value) Stored in the form, it is possible to quickly find the value based on the key

*The key-value pair of the Map exists as an object instance of the Entey type

*The key value can be repeated, but the value value cannot be repeated

3.Collections tool class

*Collections.sort() method

4.Comparable interface

*Default comparison rules, you need to implement the ComparaTo() method

5.Comparator interface

*Temporary comparison rules need to implement the Compare() method

3. Generic

The elements in the collection can be of any type Object (object reference), if you put a reference to an object into a collection, its type will be ignored and treated as an Object class;

Generics stipulate that a certain collection can only The stored objects of specific types will be type checked during compilation, and you can directly specify the type to obtain the collection elements;

For example: it is stipulated that only student classes can be stored in the collection

List<Student> stuList = new ArrayList<Student>();

It should be noted that the types limited in generic collections cannot be basic data types, such as int, etc., and their corresponding packaging classes can be used;

The above are the collection framework notes in Java Content, for more related content, please pay attention to the PHP Chinese website (www.php.cn)!