单例设计模式的几种Java实现

落日映苍穹つ 2022-05-26 08:17 203阅读 0赞

### 一、静态变量初始化实现线程安全的单例模式 ###

> `static`变量`instance`是在类被加载时初始化并仅被初始化一次，这样就可以保证只有一个instance被初始化。

public class Singleton { 
        private static Singleton instance = new Singleton();
    
        private Singleton(){}
    
        public static Singleton getInstance(){
            return instance;
        }
    
    }

### 二、经典的非线程安全单例模式实现类 ###

public class Singleton { 
        private static Singleton instance;
    
        private Singleton(){ }
    
        public static Singleton getInstance(){
            if(instance == null){
                instance = new Singleton();
            }
            return instance;
        }
    
    }

### 三、线程安全的单例模式实现类 ###

public class Singleton { 
        private static Singleton instance;
    
        private Singleton(){}
    
        public static synchronized Singleton getInstance(){
            if(instance == null){
                instance = new Singleton();
            }
    
            return instance;
        }
    
    }

### 四、高效的线程安全的单例模式实现类 ###

public class Singleton { 
        private static volatile Singleton instance;
    
        private Singleton(){}
    
        public static Singleton getInstance(){
            if(instance == null){
                //类锁
                synchronized(Singleton.class){
                    if(instance == null){
                        instance = new Singleton();
                    }
                }
            }
    
            return instance;
        }
    
    }

**写在最后：**

> 以上是我工作中常遇到的单例模式实现方式，欢迎补充…