What are the five commonly used design patterns in Java?

Five commonly used design patterns in Java: 1. Singleton design pattern; 2. Factory design pattern; 3. Agent design pattern; 4. Observer design pattern; 5. Adapter pattern.

The operating environment of this tutorial: windows7 system, java10 version, DELL G3 computer.

Five commonly used design patterns in Java:

1. Singleton design pattern

The so-called singleton design pattern is simple That is to say, no matter how the program runs, a class using the singleton design pattern (Singleton class) will always have only one instantiated object. The specific implementation steps are as follows:

(1) Privatize the construction method of the class using the singleton design pattern (modify it with private).

(2) Generate an instantiation object of this class internally and encapsulate it into a private static type.

(3) Define a static method to return an instance of this class.

2. Factory design pattern

The program adds a transition end between the interface and the subclass. Through this transition end, subclasses that implement the common interface can be dynamically obtained. Class instantiation object.

3. Agent design pattern

means that a proxy theme operates the real theme. The real theme performs specific business operations, while the proxy theme is responsible for processing other related businesses. . For example, in life, when accessing the network through a proxy, customers connect to the network through a network proxy (specific business), and the proxy server completes user permissions and access restrictions and other operations related to the Internet (related business).

4. Observer Design Pattern

The so-called observer pattern, for example, many home buyers now closely observe changes in house prices. When house prices change, all All home buyers can observe it, and the above home buyers are observers. This is the observer mode.

The above functions can be easily realized in java with the help of the Observable class and Observer interface. Of course, the implementation of this pattern is not limited to the use of these two classes.

5. Adapter pattern

If a class wants to implement an interface with many abstract methods, but it only needs to implement some of the methods in the interface to achieve the goal, Therefore, an intermediate transition class is needed at this time, but we do not want to use this transition class directly, so it is most appropriate to define this class as an abstract class, and then let future subclasses directly inherit this abstract class and then selectively override it. required methods, and this abstract class is the adapter class.

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