JAVA course 10 (Singleton design mode)

JAVA course 10 (Singleton design mode)

Miscellaneous:

If the methods in a class are static, there is no need to create objects. To prevent other programs from creating objects, You Can privatize the constructors of the current class.

class MAN{private MAN(){}}

Document Note: Command: javadoc

Only/** start to */end content can be parsed;/**/No

Path setting problems:

When you want to run a class file in more than two paths, you must set the path. Command: classpath =.; c: \ myhelp or: classpath =.; % myhelp %

Clear Path: set classpath =


Design Model: an effective solution to the problem

Singleton design mode:

Ensure the uniqueness of a class in the memory.

When multiple programs use the same configuration information object, the uniqueness of the object must be guaranteed.

How to Ensure the uniqueness of objects:

1. Do not allow other new objects
2. Create an instance of this class in this class
3. provide a method for other programs to obtain the object.

Steps:

1. privatize the constructor of this class
2. Create a class object in this class through new

3. define a common method to return the created object

Import java. util. strong; class MAN {private static MAN jo = new MAN (); // Step 2 // not all, for controllable private int x = 5; private MAN () // Step 1 {} public static MAN Creat (String key) // step 3 {if (key = "stdio") // The object is used correctly, otherwise, do not return jo; return null;} void show () {System. out. println ("ASDf") ;}} public class Main {public static void main (String [] args) {// man ss = MAN. creat (); String key = "stdio"; MAN s = MAN. creat (key );}}

The first mode of Singleton Design

// Hungry Chinese

Example:

Import java. util. exist; class Test {private static Test jo = new Test (); // step 2, // when the class is loaded, the object exists // not shared, to control private int num; private Test () // Step 1 {} public static Test Creat (String key) // step 3 {if (key = "stdio ") // if it is correct, the object will be used. Otherwise, the return jo; return null;} public void set (int num) {this. num = num;} public int get () {return num;} void show () {System. out. println ("ASDf") ;}} public class Main {public static void main (String [] args) {String key = "stdio"; Test s1 = Test. creat (key); Test s2 = Test. creat (key); System. out. println (s1 = s2); s1.set (10); s2.set (20); System. out. println (s1.get () + "" + s2.get (); // 20, because there is only one object }}

Object Memory created in the class:

Another manifestation of the singleton design model:

// Lazy. It can be used only when it is actually used. Features: delayed Loading Mode

Class Test {private static Test s = null; // The class is loaded only when the Creat method is called and the Creation conditions are met, the object will be created // that is, the singleton design mode and the delayed loading mode. Generally, the Test point is private int num; private Test () {} public static Test Creat (String key) {if (key = "stdio" & s = null) s = new Test (); // if yes, return s to the object ;} public void set (int num) {this. num = num;} public int get () {return num;} void show () {System. out. println ("ASDf") ;}} public class Main {public static void main (String [] args) {String key = "stdio"; Test s1 = Test. creat (key); Test s2 = Test. creat (key); System. out. println (s1 = s2 );}}

PS

During the interview, the interview is generally lazy.
Use the hungry Chinese style during development