1. What is the singleton pattern
The singleton pattern (Singleton Pattern) is one of the simplest design patterns in Java. The singleton pattern is: During the running of the program, some classes have at most one instance object. This pattern involves a single class that is responsible for creating its own objects while ensuring that only a single object is created. This class provides a way to access its unique objects directly, without the need to instantiate an object of the class.
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2. Implementation ideas of singleton mode
1. Staticization Instance object, let the instance object and Class object bind to each other, and can be accessed directly through the Class class object;
2. Private construction method, prohibiting the creation of multiple instances through the construction method;
3. Provide a public static method to return the only instance of this class.
3. Advantages and Disadvantages of Singleton Mode
Advantages:
1. There is only one instance in the memory, which reduces the memory overhead, especially Instances are frequently created and destroyed.
2. Avoid multiple occupation of resources.
Disadvantages:
There is no interface and cannot be inherited, which conflicts with the single responsibility principle. A class should only care about the internal logic and not how to instantiate it outside.
Four. Several different ways of writing singleton mode
1. Lazy man style
package com.yx.singleton; /** * Singleton * <p>初级原型-懒汉式</> * <p>优点:用到时再初始化</> * <p>缺点:并发下会产生多个实例</> * <p>不推荐</> * * @author yx * @date 2019/11/24 12:18 */ public class Singleton { /** * 静态化实例对象 */ private static Singleton sInstance = null; /** * 私有构造方法 */ private Singleton() { } /** * 提供一个公共的静态方法, 用来返回这个类的唯一实例. * * @return 单例对象 */ public static Singleton getInstance() { if (sInstance == null) { sInstance = new Singleton(); } return sInstance; } }
The above way of writing, in a concurrent environment, will Multiple instances occur, thread unsafe.
Enumeration method
/** * EnumSingleton * 枚举类单例模式 * * <p>优点:不需要考虑序列化的问题;不需要考虑反射的问题</> * <p>缺点:所有的属性都必须在创建时指定, 也就意味着不能延迟加载; 并且使用枚举时占用的内存比静态变量的2倍还多</> * * @author yx * @date 2019/11/24 15:09 */ public enum EnumSingleton { INSTANCE }
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